arsenic in water research paper

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Arsenic in drinking water: An analysis of global drinking water regulations and recommendations for updates to protect public health

Seth h. frisbie.

1 Department of Chemistry and Biochemistry, Norwich University, Northfield, Vermont, United States of America

Erika J. Mitchell

2 Better Life Laboratories, Inc., East Calais, Vermont, United States of America

Associated Data

All relevant data are within the paper and its Supporting Information files.

Evidence-based public health policy often comes years or decades after the underlying scientific breakthrough. The World Health Organization’s (WHO’s) provisional 10 μg/L arsenic (As) drinking water guideline was set in 1993 based on “analytical achievability.” In 2011, an additional proviso of “treatment performance” was added; a health-based risk assessment would lead to a lower and more protective guideline. Since the WHO does not require United Nations member states to submit copies of national drinking water regulations, there is no complete database of national drinking water standards or guidelines. In this study, we collated and analyzed all drinking water regulations for As from national governments worldwide. We found regulations for 176 countries. Of these countries, 136 have drinking water regulations that specify 10 μg/L As or less, while 40 have regulations that allow more than 10 μg/L of As; we could not find any evidence of regulations for 19 countries. The number of people living in countries that do not meet the WHO’s guideline constitutes 32% of the global population. Global As regulations are also strongly tied to national income, with high income countries more likely to meet the WHO’s guideline. In this study, we examined the health risk assessments that show a clear need for reducing As exposure to levels far below the current WHO provisional guideline. We also show that advances in analytical chemistry, drinking water treatment, and the possibility of accessing alternative drinking water supplies without As suggest that both low-income countries with limited resources and high-income countries with adequate resources can adopt a lower and more protective national drinking water standards or guidelines for As. Thus, we recommend that regulators and stake holders of all nations reassess the possibilities for improving public health and reducing health care expenses by adopting more stringent regulations for As in drinking water.

1. Introduction

Arsenic (As) is a common drinking water contaminant that is often found in groundwater wells [ 1 – 6 ]. Even at very low concentrations, chronic consumption of As in drinking water has been strongly associated with a variety of cancers and other adverse health effects in humans [ 7 – 13 ]. At least 226 million people in 56 countries are exposed to unsafe concentrations of As in drinking water and food [ 14 ].

It often takes years or decades for an advance in science to cause a change in public health policy [ 15 ]. Notably, we will demonstrate that all national standards and guidelines for As in drinking water are based on outdated assumptions. For example, many low-and middle-income countries still use the World Health Organization’s (WHO’s) 1963 drinking water standard for As of 50 micrograms per liter (μg/L), even though the WHO lowered its recommended maximum concentration for As to 10 μg/L in 1993 [ 16 , 17 ]. Most high-income countries use a 10 μg/L As drinking water standard, consistent with the current WHO recommended maximum concentration. However, many regulators and stakeholders may not be aware that the WHO 10 μg/L guideline is deemed “provisional” [ 17 , 18 ]. Although risk assessment data indicate a lower guideline would be more appropriate, the WHO retains the 10 μg/L for As based on an assumed practical quantification limit of routine laboratories, as well as an assumed practical drinking water treatment limit [ 17 , 18 ]. Much new technology for the testing and treatment of As has been developed since the provisional 10 μg/L WHO guideline was first set based on practical concerns rather than health data, but the provisional guideline value has not been updated since 1993 [ 17 , 18 ].

This causes a significant threat to global public health. Current research shows that more protective national standards and guidelines for As in drinking water are technologically feasible and urgently necessary to protect public health. In this study we collate all current national standards for As in drinking water into a database that can be used to examine patterns of As regulations based on geographic regions and income. We review the basis of the WHO’s drinking water guideline for As and why it is deemed “provisional”. We examine risk assessment data that indicate that an As guideline of 10 μg/L does not provide sufficient protection against cancer and other adverse health effects. Finally, we review current quantification and treatment technologies, demonstrating the technological feasibility of reducing the maximum allowable concentration of As in drinking water in both high and low income countries.

2. Materials and methods

2.1 international drinking water standards for arsenic.

In order to better understand the state of current regulations for As in drinking water worldwide, we collated all available national standards. We began with a list of the 193 United Nations member states and supplemented this list with 2 other states for which the World Bank provides income group data, Taiwan and Kosovo [ 19 , 20 ]. We then searched for official laws or decrees promulgated by these national governments regulating As in drinking water. For each country we began our search for national laws and decrees on As in drinking water at the Law Library of Congress website ( http://www.loc.gov/law/help/guide/nations.php ). When possible, the official online government gazette of a country was also used for this search. If necessary, the FAOLEX database of national laws and regulations on food, agriculture, and renewable natural resources [ 21 ], Google Scholar [ 22 ], and Google were also used for this search. We also searched catalogs of national standards agencies. When necessary, Google Translate [ 23 ] was used to translate between English and the official language of a country. Common search terms included the name of the country, the official gazette of the country, “drinking water quality standards”, “drinking water standards”, “drinking water”, “water”, “arsenic”, “μg/L”, and “mg/L” in both English and the official language of the country. We also compared our search results with those of previous partial surveys of international drinking water regulations [ 24 – 27 ].

For countries in which our search methods could not locate a national law or decree, we continued our search, seeking secondary evidence for regulations such as peer-reviewed articles, dissertations, theses, or similar documents that state a drinking water standard for As in a country. Secondary evidence of regulations was only used when primary evidence was not found. We searched for secondary evidence of regulations using the name of the country, the official gazette of the country, “drinking water quality standards”, “drinking water standards”, “drinking water”, “water”, “arsenic”, “μg/L”, and “mg/L” in both English and the official language of the country. We also used internet searches to determine the national agency or organization responsible for setting drinking water quality standards in these countries and contacted representatives of these agencies via email and Facebook in a national language requesting help obtaining the standards.

If we were unable to find either primary or secondary evidence for a drinking water regulation for As in a country, we assumed that there was most likely no national standard or guideline. There were 19 countries for which we could not find any evidence of drinking water regulations for As.

To understand the relationships between population, income, and As standards, we collated population, gross domestic product (GDP), and GDP per capita data for each country [ 20 , 28 , 29 ]. We selected 2019 population and GDP data since it is the most current data before the demographic and economic upheavals caused by the COVID-19 pandemic. Although COVID-19 was first detected during 2019, as of January, 2020, international economists were not yet expecting it to have a major impact on the world economy [ 30 ].

2.2 Data analysis and statistics

We used R version 4.1.1, “Kick Things”, released August 10, 2021 to calculate descriptive statistics and perform hypothesis testing. For hypothesis testing, we assumed a 95% confidence level for significance. Multiple statistical comparisons of the data were not made, so no corrections for multiple comparisons were applied. Figures and maps were also created with R using the R packages ggplot2 and ggmaps.

3. Results and discussion

The results of our search for national As regulations are listed in Table 1 . In addition to the name of each country and concentration of As specified in the regulation, we have also included the 2019 Gross Domestic Product (GDP) per capita from the World Bank [ 20 ], the 2019 WB income category [ 31 ], whether the stated standard is determined independently by the country or tied to international regulations or guidelines such as the WHO drinking water guideline, and when the regulation was most recently updated.

Abbreviations: CARICOM = Caribbean Community; CIS = Commonwealth of Independent States; EAS = East Africa States; EU = European Union; GCC = Gulf Cooperation Council; Gov. Org. = governmental organization (ministry, agency, department); GDP = gross domestic product; LM = Lower Middle; NA = NA; WHO = World Health Organization; UM = Upper Middle; US EPA (United States Environmental Protection Agency)

a Law/Decree includes legislation and presidential or royal decrees; Gov. Org. includes ministries and governmental agencies; Standards Org. includes standards bureaus and standards agencies.

b Standard withdrawn October 14, 2016 [ 36 ].

c Caribbean Community and Common Market (CARICOM) standard for packaged purified drinking water is 50 μg/L [ 106 ].

d The official government document lists this value as “1,0 ug/l”, which is a magnitude lower than the contemporaneous WHO value [ 122 , 123 ]. Since the other water contaminants follow the WHO values, this value is likely a typographical error for “10 ug/l”.

e As standard only currently applies to municipalities of > 500K inhabitants; to municipalities of > 50K inhabitants by 2022 and to all by 2025 [ 128 ].

f Applies specifically to bottled water [ 130 ].

g The official government document lists this value as “0.5 mg/l”, which is a magnitude higher than a previous WHO value [ 131 , 132 ]. Since the document references the WHO guidelines, and a former WHO guideline for As was 50 μg/L, this value is likely a typographical error for “0.05 mg/l”.

h Permissible limit in the absence of alternative source: 50 μg/L [ 152 ].

i Author suggests that East Timor uses WHO guidelines as local standards [ 190 ].

j Standards are specifically for the Emirate of Abu Dhabi [ 196 ].

k The maximum contaminant level for As in bottled water is 50 μg/L [ 204 ].

l A Nauru government document states that there are no standards [ 206 ], but the 2018 WHO survey noted that Nauru uses WHO guidelines as standards [ 18 , 24 ].

m A secondary source states that there are no national standards [ 214 ], but the 2018 WHO survey noted that Tonga uses WHO guidelines as standards [ 18 , 24 ].

n The decree states that in some cases 50 μgl/L is the maximum allowable threshold taking into account the detection limit of the analytical equipment [ 218 ].

o Applies specifically to private water supplies [ 263 ].

3.1 Arsenic regulations

We found evidence of regulations for a maximum allowable concentration of As in drinking water for 176 countries. There were 19 countries for which we could not find any evidence of drinking water regulations. By comparison, in a 2015 survey of global drinking water regulations, the WHO found regulations for As in 102 out of 104 countries [ 24 ] while the International Water Resources Association’s 2018 comparison of water quality guidelines included drinking water standards for 10 countries [ 25 ].

Of the As regulations that we found, the lowest maximum allowable concentration of As was 1 μg/L, the highest was 500 μg/L, and the mode was 10 μg/L. The lowest maximum allowable concentration for As of 1 μg/L may be a typographical error in the government document establishing this allowable concentration since the other contaminants listed in the document followed the values listed in the WHO’s drinking water guidelines at the time [ 122 , 123 ]. The highest maximum allowable concentration of 500 μg/L was also likely a typographical error in the official government record [ 131 ]. If these 2 likely errors are set aside, the lowest maximum concentration for As was 5 μg/L and the highest maximum concentration was 300 μg/L. When the likely typographical errors are adjusted to their probable intended values, 2 countries have a maximum allowable concentrations less than 10 μg/L, 134 countries have maximum allowable concentrations of 10 μg/L, and 40 countries have maximum allowable concentrations of greater than 10 μg/L. For all statistical analyses that follow, we retained the published regulatory values without adjustments for possible typographical errors.

The oldest regulation for As in drinking water currently in force is dated 1985 [ 142 , 143 , 187 ], while the most recent regulation dates to 2021 [ 112 ]. The average date of the regulations is 2011, while the mode is 2017 ( Fig 1 ). Arsenic standards are established by national legislation or decree in 85 countries, ministries or agencies in 58 countries, and national standards boards in 33 countries. Many standards published by national standards boards are copyrighted documents and must be purchased or licensed for a fee in order to be accessed.

3.2 Arsenic regulations, population, and per capita income

Seventy percent (136) of the 195 countries in our survey have regulations for As in drinking water that are equal to or more protective than the WHO’s drinking water guideline of 10 μg/L, while 21% (40) of the 195 countries have regulations that are less protective than the WHO’s 10 μg/L guideline, and we could not find regulations for 10% (19) of the 195 countries. Sixty-six percent of the world’s population lives in countries with As drinking water regulations equal to or more protective than the WHO’s 10 μg/L guideline, 32% live in countries with regulations that are less protective than the WHO’s 10 μg/L guideline, and 2% live in countries where we could not find evidence of a drinking water guideline for As ( Fig 2 ).

Arsenic regulations are also strongly tied to national income as represented by GDP per capita. The sum of all GDPs of the countries with 2019 GDP data and an As regulation equal to or more protective than the WHO guideline of 10 μg/L divided by the sum of the population of these countries was $13,587 per capita. In contrast, the sum of all GDPs of countries with 2019 GDP data and an As regulation less protective than the WHO guideline divided by the sum of the population of these countries was $7,601 per capita. The sum of all GDPs of countries for which we had 2019 GDP data but could not find an As regulation divided by the sum of the population of these countries was $1,227 per capita. The GDPs per capita of countries with As regulations equal to or more protective than the WHO guideline of 10 μg/L were significantly higher ( n = 129, M = $17,678) than those of countries with As regulations less protective than the current 10 μg/L WHO guideline ( n = 36, M = $5,384) (F(2,177) = 7.55, p < .001).

A graph of GDP per capita versus national drinking water standard or guideline for As is shown in Fig 3 . Maps of GDP per capita and national drinking water standards or guidelines for As are shown in Figs ​ Figs4 4 and ​ and5, 5 , respectively.

The World Bank classifies economies into one of 4 groups: low income, lower middle income, upper middle income, and high income [ 31 ]. We found no difference in recency of As regulations by income group (F(3,175) = 0.63, p = 0.60). For the countries that have As regulations, the mean As regulation for low income countries was 21 μg/L, for lower middle income countries the mean was 24 μg/L, for upper middle income countries the mean was 38 μg/L, and for high income countries the mean was 11 μg/L ( Fig 6 ). An analysis of variance (ANOVA) on these means yielded significant variation between income classes (F(3, 172) = 3.15, p = .03). A post hoc Tukey test showed that the mean As standard of the high income class differed significantly from that of the upper middle income class (p = .01) while the remaining differences were not significant (p>0.05).

Sixteen countries tie their maximum allowable As concentrations directly to the WHO drinking water guidelines. A large number of other countries have maximum allowable As concentrations that equal the current or previous WHO drinking water guidelines. This underscores the importance of the WHO drinking water guidelines for protecting the health of world citizens.

3.3 The drinking water guideline set by the World Health Organization

The WHO first established a drinking water standard for As, 200 μg/L, in 1958 based on health concerns [ 123 , 265 ]. As adverse health effects from As exposure received more study, this As drinking water standard was lowered to 50 μg/L in 1963 [ 16 , 123 ]. In 1971, the World Health Organization (WHO) deemed its 50 μg/L As standard a “tentative limit” [ 132 ] and noted, “Some epidemiological studies have suggested that arsenic is carcinogenic but no real proof of the carcinogenicity to man of arsenic in drinking-water has been forthcoming. It would seem wise to keep the level of arsenic in drinking-water as low as possible” [ 132 ].

In 1971, 50 μg/L was “as low as possible” for a limit because the available methods for the routine analysis of As in drinking water were not accurate, precise, sensitive, or affordable enough to reliably measure lower concentrations [ 132 ]. For example, the recommended method of polarographic estimation was often not accurate due to interferences, and the incomplete reduction of analyte [ 132 , 266 ]. Similarly, the commonly used spectrophotometric determination of As by the silver diethyldithiocarbamate (AgSCSN(CH 2 CH 3 ) 2 ) method was not precise due to the sometimes incomplete generation of arsine gas (AsH 3 (g)) from the sample matrix [ 132 , 267 ]. In contrast, atomic absorption spectroscopy (AAS) was accurate, precise, and sensitive, but not affordable in many low-income countries [ 132 , 267 ].

In 1984, the WHO began publishing drinking-water “guidelines” instead of “standards” [ 268 ]. Guidelines were intended to provide guidance to national regulators and stakeholders, but they are specifically not to be taken as international standards. National regulators are encouraged to take local conditions, resources, and hazards into account when setting national standards [ 268 , 269 ]. The 1984 WHO drinking-water guideline for As was maintained at 50 μg/L, the former WHO standard [ 268 ].

In 1993, the WHO replaced its earlier “tentative limit” of 50 μg/L with a “provisional guideline” of 10 μg/L for As in drinking water [ 17 ]. By this time, a skin cancer risk in humans was known, and other cancer risks were suspected. “Inorganic arsenic is a documented human carcinogen and has been classified by IARC [International Agency for Research on Cancer] in Group 1 [‘This category is used when there is sufficient evidence of carcinogenicity in humans.’]. A relatively high incidence of skin and possibly other cancers that increase with dose and age has been observed in populations ingesting water containing high concentrations of arsenic” [ 17 ]. The WHO calculated a health-based value of 0.17 μg/L, but noted that this value was below the practical quantification limit of 10 μg/L [ 17 ]. Therefore, the 10 μg/L drinking water guideline for As was initially “provisional” because of what is now called “analytical achievability” [ 17 , 269 ]. Thus, the 1993 WHO 10 μg/L drinking water guideline for As was based on practical analytical concerns rather than health data, since health data would have led to a lower guideline [ 17 ].

The WHO has maintained this 10 μg/L provisional drinking water guideline for As in all subsequent editions and addendums of Guidelines for Drinking-water Quality since 1993 [ 18 , 123 , 270 – 272 ]. In 2006, the WHO stated that As in drinking water not only causes skin cancer, but also causes bladder and lung cancers [ 271 ]. “There is overwhelming evidence from epidemiological studies that consumption of elevated levels of arsenic through drinking-water is causally related to the development of cancer at several sites, particularly skin, bladder and lung” [ 271 ]. In 2011, the WHO added kidney cancer to this list [ 272 ]. “The International Programme on Chemical Safety (IPCS) concluded that long-term exposure to arsenic in drinking-water is causally related to increased risks of cancer in the skin, lungs, bladder and kidney, as well as other skin changes, such as hyperkeratosis and pigmentation changes” [ 272 ]. However, the WHO did not lower their drinking water guideline for As “because [the] calculated guideline value is below the achievable quantification level” [ 272 ]. Again, “guideline values are not set at concentrations of substances that cannot reasonably be measured. In such circumstances, provisional guideline values are set at the reasonable analytical limits” [ 269 , 272 ].

In 2011, the WHO added a second provision to its provisional 10 μg/L drinking water guideline for As [ 272 ]. This second provision is based on “treatment performance” [ 272 ]. More specifically, “It is technically feasible to achieve arsenic concentrations of 5 μg/l or lower using any of several possible treatment methods. However, this requires careful process optimization and control, and a more reasonable expectation is that 10 μg/l should be achievable by conventional treatment (e.g. coagulation)” [ 272 ]. In 2017, the WHO maintained its 10 μg/L provisional drinking water guideline for As, the “analytical achievability” provision for this guideline, and the “treatment performance” provision for this guideline [ 18 , 269 ].

In summary, the current WHO 10 μg/L provisional drinking water guideline for As is not set according to a health-based risk assessment, since this would require a lower maximum concentration, but rather, it is based on the detection limits for the routine analysis of As in drinking water, which have not been updated since 1993, and treatment technologies for As, which have not been updated since 2011 [ 18 , 272 ].

3.4 Health-based drinking water guidelines

In 2000, the United States Environmental Protection Agency (U.S. EPA) proposed a non-enforceable health-based goal, or Maximum Contaminant Level Goal (MCLG) for As of 0 μg/L [ 273 ]. This 0 μg/L MCLG remains in force [ 135 ]. In 1999, the U.S. EPA noted that there was a Practical Quantitation Limit (PCL) for As of 3 μg/L [ 274 ]. However, instead of using this PQL as the enforceable standard Maximum Contaminant Level (MCL), 5 μg/L was proposed as a national standard based on a cost/benefit analysis [ 273 ]. After this proposed MCL of 5 μg/L was set out for public comment, the MCL was raised to 10 μg/L before being adopted as the national standard, over the objections of the U.S. EPA’s own Scientific Advisory Board, who argued for a lower MCL [ 275 , 276 ].

In contrast, the California Environmental Protection Agency (CalEPA) has set a public health goal (PHG) of 0.004 μg/L for As in drinking water [ 7 , 8 ]. This PHG is based on human health effects; it is not influenced by detection limits or the performance of drinking water treatment systems. Under California law, a PHG must be based on current scientific evidence and give a negligible risk of adverse health effects over a lifetime of exposure [ 277 ]. In addition, a PHG must not consider economic, technical, or other societal factors [ 277 ]. As a result, the CalEPA 0.004 μg/L PHG is 2,500 times lower than the WHO provisional drinking water guideline and the U.S. EPA drinking water standard of 10 μg/L.

More specifically, the CalEPA PHG is based on the risk of death from lung and bladder cancers after a lifetime of exposure to As in drinking water [ 8 ]. These risks were calculated from epidemiological studies in Taiwan, Chile, and Argentina (Eqs 1 , 2 , 3 , 4 , 5 and 6 ) [ 8 ]. Since the risk of death from lung and bladder cancers is greater than that from skin cancer, kidney cancer, and noncancer health effects, the risks from these 3 less significant effects were not factored into the CalEPA PHG (Eqs 1 and 2 ) [ 8 ].

The nonsignificant digits, “75”, are shown as a subscript (Eqs 1 , 2 , 3 , 4 , 5 and 6 ). These nonsignificant digits are included in all steps of a calculation to prevent rounding error. The CalEPA rounded their PHG to 1 significant figure as follows ( Eq 2 ) [ 8 ].

This 0.004 μg/L PHG is estimated to result in 1 excess cancer death in 1,000,000 people ( Eq 2 ) [ 8 ]. That is, if 1,000,000 people drank water with 0.004 μg of As/L over their lifetimes, it is estimated that 1 of these 1,000,000 people would die from cancer because of this exposure to As. The excess death could be prevented if the dose of the carcinogen is lowered or eliminated [ 8 ].

In contrast, the 10 μg/L value used as the WHO provisional drinking water guideline and the U.S. EPA MCL is estimated to result in 2,500 excess cancer deaths in 1,000,000 people ( Eq 3 ), or in 1 excess cancer death in 400 people ( Eq 4 ).

By comparison, the National Research Council estimated that drinking 10 μg/L of As over a lifetime results in 3,700 excess cancer deaths in 1,000,000 males and 3,000 excess cancer deaths in 1,000,000 females ( Eq 3 ) [ 8 ].

The 50 μg/L value still used by many countries as national drinking water standards is estimated to result in 12,000 excess cancer deaths in 1,000,000 people ( Eq 5 ), or 1 excess cancer death in 81 people ( Eq 6 ).

3.5 Low-cost methods for improving public health by reducing arsenic exposure

3.5.1 advances in inexpensive analytical chemistry methods.

One reason for using a 50 μg/L drinking water standard for As instead of the more protective WHO 10 μg/L guideline is the high cost of atomic absorption spectrometers or other sophisticated instruments for measuring total As to 10 μg/L or lower. However, recent developments in analytical methods now make it possible to quantify As to 10 μg/L or lower without expensive equipment.

3.5.2 Spectrophotometry

One example of a low-cost method for quantifying As to 10 μg/L or lower without expensive equipment is the arsenomolybdate method, validated in 2005 [ 267 ]. By design, the arsenomolybdate method uses the same equipment as the commonly used silver diethyldithiocarbamate (AgSCSN(CH 2 CH 3 ) 2 ) method for measuring As [ 267 , 278 ]. In the arsenomolybdate method, As is removed from the sample by reduction to arsine gas (AsH 3 (g)), collected in an absorber by oxidation to arsenic acid (H 3 AsO 4 ), colorized by a sequential reaction to arsenomolybdate, and quantified by spectrophotometry at 835 nm (nanometers) [ 267 ]. The method detection limit is 7 μg/L ( Table 2 ) [ 267 ]. This detection limit is intended to equal the “concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than 0” [ 279 , 280 ]. In summary, the arsenomolybdate method is more accurate, precise, and environmentally safe than the AgSCSN(CH 2 CH 3 ) 2 method; and it is more accurate and affordable than the graphite furnace atomic absorption spectroscopy (GFAAS) method [ 267 ].

These cancer risks are in bold font and rounded to 2 figures.

Other advances in inexpensive analytical chemistry methods include the use of cationic dyes, such as malachite green (C 6 H 5 C(C 6 H 4 N(CH 3 ) 2 ) 2 + ), that react with oxyanions, such as derivatized As and derivatized phosphorus (P), to form an ionic solid. These solids are either suspended with a surfactant or dissolved with an organic solvent and measured by spectrophotometry [ 281 – 283 ]. More specifically, one method for the determination of total As uses an arsenoantimonomolybdenum blue-malachite green complex [ 283 ]. This complex is suspended with Triton™ X-350 and analyzed at 640 nm [ 283 ]. The detection limit is 4 μg/L and is defined as the concentration of standard solution that has a 0.01 absorbance ( Table 2 ) [ 283 ]. This method is subject to interferences unless the As is removed from the sample by reduction to AsH 3 gas before color development [ 283 ]. Another method for the determination of total As uses a molybdoarsenate-malachite green complex [ 282 ]. This complex is concentrated by filtration onto a nitrocellulose membrane filter [ 282 ]. This complex and filter are dissolved with 2-methoxyethanol (methyl cellosolve; CH 3 OCH 2 CH 2 OH), and the filtrate is analyzed at 627 nm [ 282 ]. The detection limit is 0.3 μg/L; however, the criteria used to calculate this detection limit was not given ( Table 2 ) [ 282 ]. Interference from phosphate is corrected by a selective reduction procedure, interference from ferric iron (Fe(III)) is corrected by a cation exchange procedure, and interference from silicate is corrected by an acidic digestion procedure [ 282 ]. Alternatively, all of these interferences are corrected if As is removed from the sample by reduction to AsH 3 gas before color development.

More recently, another cationic dye, ethyl violet (C(C 6 H 4 N(CH 2 CH 3 ) 2 ) 3 + ), was reacted with derivatized oxyanions of As to form suspended particles of ionic complexes [ 284 , 285 ]. More specifically, one method for the determination of total As uses a molybdoarsenate-ethyl violet complex [ 284 ]. This complex forms suspended microparticles and an apparently homogenous blue solution [ 284 ]. Prior to color development, interference from phosphate is corrected by an anion exchange procedure, and interference from silica is corrected by reaction with sodium fluoride (NaF) [ 284 ]. After color development, the excess dye is converted to a colorless carbinol species in strong acid and the molybdoarsenate-ethyl violet complex is analyzed at 612 nm [ 284 ]. This decolorization of excess dye significantly reduces the absorbance of reagent blanks and permits a 4 μg/L detection limit ( Table 2 ) [ 284 ]. This detection limit is defined as 3σ/ m , “where σ is the standard deviation of 5 measurements of the reagent blank, and m is the slope of the calibration graph” [ 284 ]. This method was modified and uses ethyl violet, an isopolymolybdate-iodine tetrachloride complex, and molybdoarsenate to form suspended nanoparticles that are analyzed at 550 nm as a determination of total As [ 285 ]. Prior to color development, interference from ferric iron is corrected by reaction with ethylenediaminetetraacetic acid (EDTA), interference from phosphate is corrected by an anion exchange procedure, and interference from silica is corrected by reaction with NaF [ 285 ]. The detection limit is 0.5 μg/L ( Table 2 ) [ 285 ]. This detection limit is defined as 3σ/ m [ 285 ].

Another method for the determination of total As uses a reduction and selective extraction of arsenite, As(III), into an ionic liquid functionalized with gold (Au) nanoparticles that are analyzed visually or potentially with a spectrophotometer [ 286 ]. The reducing agent is ascorbic acid (C 6 H 8 O 6 ) [ 286 ]. The ionic liquid is prepared by mixing ultrapure water (in this case, resistivity = 18.3 MΩ⋅cm), tetradecyl (trihexyl) phosphonium chloride (Cyphos® IL-101; [C 14 (C 6 ) 3 P]Cl), and Triton™ X-114 [ 286 ]. This ionic liquid is functionalized by adding chloroauric acid (HAuCl 4 ) and potassium tetrahydroborate (KBH 4 ) [ 286 ]. The functionalized ionic liquid is red in the absence of As(III) and blue in the presence of As(III) [ 286 ]. The estimated detection limit by naked eye is 7.5 μg/L ( Table 2 ) [ 286 ]. This method is highly selective; 1.0 micromolar (μM) concentrations of K + , Na + , Ca 2+ , Mg 2+ , Al 3+ , Ni 2+ , Fe 3+ , Cr 3+ , Zn 2+ , Mn 2+ , Pb 2+ , Cd 2+ , Hg 2+ , SO 4 2− , PO 4 3− , CO 3 2− , NO 2 − , and SiO 3 2− do not significantly interfere [ 286 ]. Higher, but unspecified concentrations, of Cl − , NO 3 − , and SCN − do not significantly interfere [ 286 ].

3.5.3 Summary of advances in inexpensive analytical chemistry methods

In summary, no country needs to use the less protective 50 μg/L standard or guideline due to the expense of analytical chemistry methods. There are many affordable methods for measuring total As to the more protective WHO 10 μg/L provisional drinking water guideline, or to concentrations as low as 0.3 μg/L ( Table 2 ).

3.5.4 Advances in inexpensive drinking water treatment technologies

Another reason for using a 50 μg/L drinking water standard instead of the more protective WHO 10 μg/L guideline is the high expense of drinking water treatment systems. However, advances in inexpensive drinking water treatment technologies have produced technologies that can now remove As to concentrations that are lower than 10 μg/L [ 287 ]. Selected examples of these advances follow.

Batch rectors used optimized pH adjustment, oxidation, coagulation, and filtration to economically remove As from drinking water to “about 5 μg/L” during field trials of 10 households and 6 schools in Assam, India [ 288 ]. Sodium bicarbonate (NaHCO 3 ) was used to adjust pH, potassium permanganate (KMnO 4 ) was used to oxidize ambient As(III) and Fe(II) to relatively insoluble As(V) and Fe(III), and iron (III) chloride (FeCl 3 ) was used to coagulate the oxidized As and Fe [ 288 ]. The treated water was allowed to settle for 1 to 2 hours [ 288 ]. The supernatant was filtered through sand-gravel filters [ 288 ]. The households each used a 10 L batch rector, 5 schools each used a 25 L batch reactor, and 1 school used a 200 L batch reactor [ 288 ]. The concentration of As in the influent ranged from 100 μg/L to 240 μg/L [ 288 ]. The concentration of As in the effluent was less than 5 μg/L if the initial concentration of Fe in the influent was less than 1,000 μg/L, and the concentration of As in the effluent was less than 8 μg/L if the initial concentration of Fe in the influent was greater than 2,500 μg/L [ 288 ]. The estimated recurring cost per cubic meter (m 3 ) of treated water was approximately US $0.16 per/m 3 [ 288 ].

An electrocoagulation batch reactor economically removed As from drinking water to concentrations that were always less than 5 μg/L during a 3.5 month field trial in West Bengal, India [ 289 ]. More specifically, electrolytic oxidation of a sacrificial iron (Fe) anode produced Fe(III) precipitates. These Fe(III) precipitates reacted with As in the influent and produced As-Fe(III) precipitates. These As-Fe(III) precipitates aggregated or flocculated together. These flocs were mixed with a small amount of alum and removed by gravitational settling [ 289 ]. The concentration of As in the influent was 266 ± 42 μg/L and the average concentration of As in the effluent was 2.1 ± 1.0 μg/L [ 289 ]. This batch reactor treated 31,000 L (50 batches) of drinking water during the 3.5 month field trial [ 289 ]. The cost of treated water was US $0.83/m 3 to US $1.04/m 3 [ 289 ].

Above ground adsorbent filters economically removed As from drinking water to concentrations that were consistently less than 10 μg/L during field trials of 20 households and 3 schools in West Bengal, India [ 290 ]. These filters were made of activated carbon, charcoal, fine granular sand, activated laterite, and raw laterite [ 290 ]. Laterites are highly weathered soils that are dominated by clay sized particles of iron hydrous oxides and aluminum hydrous oxides [ 291 ]. The laterite was activated by sequential treatment with hydrochloric acid (HCl) and sodium hydroxide (NaOH) [ 290 ]. The concentration of As in the influent ranged from 50 μg/L to 500 μg/L [ 290 ]. The concentration of As in the effluent was always less than 10 μg/L [ 290 ]. These filters have a relatively large As removal capacity, 32.5 milligrams (mg)/g, and as a result have a relatively long service life, at least 5 years [ 290 ]. The cost of the treated water was less than US $0.35/m 3 [ 290 ].

Below ground adsorbent filters economically removed As from drinking water to concentrations that were consistently less than 10 μg/L during field trials of 4 households in Hangjinhouqi County, Inner Mongolia, China [ 292 ]. These filters were made by mixing 1 mass unit of a locally abundant limestone with 2 mass units of a locally abundant Fe-mineral (hematite and goethite) [ 292 ]. This mixture was placed below ground, around the well screen of a conventional tube well [ 292 ]. The limestone likely increased the pH of the groundwater [ 293 ]. This increase in pH likely enhanced the oxidation of soluble As(III) with dissolved oxygen (O 2 (g)) to make insoluble As(V) [ 294 ]. This As(V) was removed from the groundwater by precipitation with the dissolved calcium (Ca 2+ (aq)) from the limestone and by adsorption to the surface of the Fe-mineral [ 292 ]. The concentration of As in the unfiltered groundwater ranged from 318 μg/L to 635 μg/L [ 292 ]. The concentration of As in the filtered groundwater was always less than 10 μg/L [ 292 ]. “The filtration system was continuously operated for a total volume of 365,000 L, which is sufficient for drinking water supplying a rural household of 5 persons for 5 years at a rate of 40 L per person per day” [ 292 ]. The cost of the treated water was less than US $0.10/m 3 [ 292 ].

A groundwater extraction, aeration, and reinjection system economically removed As from drinking water to concentrations that were consistently less than 10 μg/L during a village scale field trial in West Bengal, India [ 295 ]. More specifically, groundwater was extracted from the aquifer with a submersible electric pump [ 295 ]. This groundwater was aerated by spraying it into an above ground plastic tank with “ordinary plastic shower heads” and letting it sit in the tank for at least 30 minutes [ 295 ]. The final concentration of O 2 (aq) in this aerated water ranged from 4 mg/L to 6 mg/L [ 295 ]. Approximately, 15% to 20% of this aerated water as reinjected into the aquifer by gravity, and the remaining 80% to 85% of this aerated water was used for drinking [ 295 ]. The concentration of As in the influent was not clearly specified [ 295 ]. The concentration of As in the effluent was always less than 10 μg/L [ 295 ]. The cost of the treated water was US $0.50/m 3 [ 295 ].

In summary, no country needs to use the less protective 50 μg/L standard or guideline due to the expense of treatment technologies. There are many affordable methods for treating water to reduce As concentrations to lower than 10 μg/L ( Table 3 ).

3.6 Methods for improving public health by reducing arsenic exposure that require higher expenditures

3.6.1 other advances in analytical chemistry methods.

Some countries use a 10 μg/L drinking water standard or guideline because they assume that this continues to be the limit of quantification for routine analytical chemistry laboratories. However, recent advances in analytical chemistry have developed methods that can be used in routine laboratories with detection limits that are at 0.1 μg/L or less [ 18 , 296 ]. With these advances 10 μg/L As should no longer be considered the practical limit of quantification, so revised As standards or guidelines could be more protective of public health.

3.6.2 Inductively coupled plasma-mass spectrometry

Advances in inductively coupled plasma-mass spectrometry (ICP-MS) give detection limits for total As that are at 0.1 μg/L or less [ 18 , 296 ]. Moreover, ICP-MS is commonly used in routine drinking water testing laboratories because it can simultaneously measure the concentrations of almost all of the elements on the periodic table. This reduces cost by allowing each sample to be analyzed for multiple elements in just a few seconds.

An ICP-MS ionizes the As or other analytes in an inductively coupled plasma (ICP) and then separates and quantifies these ions in a mass spectrometer (MS) [ 296 ]. The drinking water sample is turned into an aerosol and delivered to an argon (Ar) plasma [ 296 ]. This plasma is a flame like object at the top of an ICP torch, and has a sufficient concentration of Ar cations (Ar + (g)) and free electrons (e − (g)) to make the gas electrically conductive ( Eq 7 ) [ 296 ].

This torch is surrounded by an induction coil [ 296 ]. This coil transmits power from a radio frequency (RF) generator to the plasma [ 296 ]. This energy maintains the ionization of the Ar gas, and the temperature of the plasma from about 5,500 kelvin (K) to 8,000 K [ 296 ]. These temperatures are approximately 2 or 3 times hotter than all flame spectroscopic methods [ 296 ]. As a result, these higher temperatures help make ICP-MS more sensitive than flame atomic absorption spectrometry (FAAS), flame atomic emission spectrometry (FAES), and flame atomic fluorescence spectrometry (FAFS) [ 296 ]. The reaction for the ionization of As in a plasma follows ( Eq 8 ).

These Ar + (g; Eq 7 ) ions, As + (g; Eq 8 ) ions, and any other ions exit the ICP and enter the MS [ 296 ]. An MS is a mass filter and a mass detector [ 296 , 297 ]. The most common type of MS used in atomic mass spectroscopy is the quadrupole mass analyzer [ 296 ]. This analyzer uses direct current (DC) and radiofrequency (RF) fields to filter ions [ 296 , 297 ]. These ions are directed in between 4 parallel rods, the quadrupole [ 296 , 296 ]. These rods are connected to a source of variable DC voltages; 2 rods are positively charged and 2 rods are negatively charged [ 296 ]. In addition, variable RF alternating current (AC) voltages are applied to each pair of rods [ 296 ]. The DC and AC voltages on the rods are simultaneously changed; however, the ratio of these voltages is held constant [ 296 ]. This makes the ions oscillate between the rods [ 296 ]. At any instant, only the ions with the desired mass and charge exit the quadrupole and are detected at an ion transducer; all other ions hit the rods, are converted to 0 charge, and are not detected [ 296 ]. In this way, an entire spectrum of atomic masses can be scanned in less than 0.1 seconds [ 296 ]. Ultimately, the MS detector measures the ratio of mass to charge ( m/z ) for each cation [ 296 – 297 ]. Since ions with multiple charges are rarely produced, the charge ( z ) is normally assumed to equal 1 and m/z is normally the mass of the cation [ 296 – 297 ].

The only naturally occurring isotope for As is 75 As; that is, all of the As in nature has 75 protons and neutrons [ 298 ]. Therefore, all of the As in nature has m/z = 75. Unfortunately, if a drinking water sample has chlorine (Cl), calcium (Ca), or sulfur (S), these common atoms can react with the plasma to form 40 Ar 35 Cl + (g), 38 Ar 37 Cl + (g), 37 Cl 2 1 H + (g), 40 Ca 35 Cl + (g), or 40 Ar 34 S 1 H + (g) [ 299 , 300 ]. These are polyatomic interferences; they all have m/z = 75 and cannot be distinguished from 75 As + (g) [ 299 , 300 ]. No other isotope of As can be used to eliminate this systematic error [ 298 ]. Mathematical corrections can be used to estimate the contribution of these polyatomic interferences to the signal at m/z = 75; however, the combined uncertainties in these corrections tend to inflate the detection limit [ 301 ].

Fortunately, advances in collision/reaction cell (C/RC) technology are being used to eliminate these polyatomic interferences and give lower detection limits [ 301 , 302 ]. If a polyatomic ion exits an ICP, enters a C/RC, and collides with an inert gas, such as helium (He(g)), the interference can be eliminated by breaking the polyatomic ion apart (collision-induced dissociation, CID) or by slowing the polyatomic ion down (kinetic energy discrimination, KED) [ 300 ]. Or if a polyatomic ion exits an ICP, enters a C/RC, and collides with a reactive gas, such as hydrogen (H 2 (g)), the interference can be eliminated by changing the mass of the polyatomic ion [ 300 ]. For example, an Agilent Technologies 7500c ICP-MS using a C/RC with 0.5 mL/minute of He(g) and 3.8 mL/minute of H 2 (g) eliminated interferences from 1 g/L of sodium chloride (NaCl) and gave a 0.025 μg/L detection limit for total As ( Table 4 ) [ 302 ]. In this case, this detection limit is the lowest concentration that can be quantified at the 99.86% confidence level [ 302 , 303 ]. This 0.025 μg/L detection limit is 400 times less than a 10 μg/L drinking water standard ( Table 4 ).

Another advance uses flow injection analysis (FIA) and a knotted reactor to remove interference precursors from the sample matrix and concentrate total inorganic As before analysis by ICP-MS [ 304 ]. Arsenate (As(V)) was reduced to arsenite (As(III)) in a solution of 1% (mass/volume) L-cysteine (HSCH 2 CHNH 2 COOH) and 0.03 molar (M) nitric acid (HNO 3 ) [ 304 ]. This As(III) was complexed with a solution of 0.1% (mass/volume) ammonium pyrrolidine dithiocarbamate ((CH 2 ) 4 NCS 2 NH 4 ) [ 304 ]. This complex was absorbed on the inner wall of a knotted reactor, in this case a 150-centimeter (cm) long by 0.5-millimeter (mm) inside diameter (ID) piece of polytetrafluoroethylene (PTFE) tubing [ 304 ]. The interference precursors from the sample matrix were washed away and the total inorganic As was concentrated when this complex was absorbed in the reactor [ 304 ]. This complex was desorbed from the reactor with 1 molar (M) HNO 3 and eluted into a Perkin-Elmer-Sciex ELAN 5000 ICP-MS [ 304 ]. This gave a 0.029 μg/L detection limit for total inorganic As ( Table 4 ) [ 304 ]. This detection limit is defined as 3 times the sample standard deviation ( s ), presumably from the measurement of reagent blanks [ 304 ].

3.6.3 Inductively coupled plasma-tandem mass spectrometry

Advances in inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) give detection limits for total As that are 0.01 μg/L or less [ 301 ]. The first MS is typically used as a mass filter and lets through only ions at m/z = 75 ( 75 As + (g), 40 Ar 35 Cl + (g), 38 Ar 37 Cl + (g), 37 Cl 2 1 H + (g), 40 Ca 35 Cl + (g), and 40 Ar 34 S 1 H + (g)) [ 299 – 301 ]. If present, these ions enter a C/RC and the 75 As + (g) selectively reacts with either oxygen (O 2 (g)) or fluoromethane (CH 3 F(g)) to produce 75 As 16 O + (g) at m/z = 91 or 75 As 12 C 1 H 2 + (g) at m/z = 89, respectively [ 301 , 305 , 306 ]. The second MS is used to filter the interferences at m/z = 75, and quantify the 75 As 16 O + (g) at m/z = 91 or 75 As 12 C 1 H 2 + (g) at m/z = 89 [ 301 , 305 , 306 ]. This use of 2 mass spectrometers in tandem increases sensitivity and lowers the detection limit [ 301 ].

For example, if O 2 (g) is used in the C/RC, a 0.0016 μg/L detection limit for total As was observed ( Table 4 ) [ 306 ]. This detection limit is defined as the lowest concentration that can be quantified at the 99.7% confidence level [ 303 , 305 ]. If 10% CH 3 F(g) and 90% He(g) are used in the C/RC, a 0.0002 μg/L detection limit for total As was observed ( Table 4 ) [ 306 ]. This detection limit is defined as 3 s / m , where s is the sample standard deviation from 10 measurements of a reagent blank, and m is the average slope from 10 calibration graphs [ 306 ].

ICP-MS/MS is a very new technology; the first commercial instruments were sold in 2012 [ 301 ]. As a result, ICP-MS/MS is mostly used for research and is not commonly used in drinking water testing laboratories. However, ICP-MS/MS will likely become more commonly used for drinking water testing in the future.

3.6.4 Hydride generation-gas chromatography-photoionization detection

Advances in hydride generation-gas chromatography-photoionization detection (HG-GC-PID) give a detection limit for total inorganic As at 0.00082 μg/L [ 307 ]. This detection limit is defined as 3 s , where s is the sample standard deviation from 5 measurements of a reagent blank [ 307 ]. The hydride generation step uses 50 mL of sample, 2.0 mL of concentrated hydrochloric acid (HCl), 3.0 mL of 1.0 M potassium iodide (KI), and 4.0 mL of 4.0% (weight/volume) sodium borohydride (NaBH 4 ) to reduce arsenate (As(V)) and arsenite (As(III)) to arsine gas (AsH 3 (g)) [ 307 ]. Helium (He(g)) is used as a carrier gas to move the AsH 3 (g) from the reaction vessel, to a trap at −50°C, a trap at −196°C, a gas chromatograph (GC), and a photoionization detector (PID) [ 307 ]. If present, water vapor (H 2 O(g)) is an interference and is removed from the AsH 3 (g) in a trap that is cooled to −50°C with dry ice (CO 2 (s)) and 2-propanol (CH 3 CHOHCH 3 ) [ 307 ]. After this step, the AsH 3 (g) is concentrated in a trap that is cooled to −196°C with liquid nitrogen (N 2 (l)) [ 307 ]. If present, stibine gas (SbH 3 (g)) is an interference and is separated from the AsH 3 (g) in a GC with a Carbopack™ B HT column [ 307 ]. Finally, AsH 3 (g) is quantified using a 10.2 electron volt (eV) PID [ 307 ].

3.6.5 Summary of other advances in analytical chemistry methods

In summary, no country needs to use the less protective 10 μg/L standard or guideline due to the expense of analytical chemistry methods. There are many methods for measuring total As to lower and the more protective concentrations ( Table 4 ).

3.6.6 Other advances in drinking water treatment technologies

Another reason for continuing to use a 10 μg/L drinking water standard is “treatment performance” [ 18 , 272 ]. However, recent advances in treatment technologies allow removal of As to concentrations that are significantly lower than 10 μg/L and would allow lower standards that would be more protective of public health. Selected examples of these advances follow.

By law, the Netherlands has a 10 μg/L drinking water standard [ 248 ]; however, the Netherlands voluntarily uses a less than 1 μg/L drinking water guideline to better protect public health. In 2015, “the Association of Dutch Drinking water Companies (Vewin) voluntarily agreed on a guideline of <1 μg/L for As in drinking water” [ 308 ]. “This policy is based on a two-step assessment of As in drinking water, including i) an assessment of excess lung cancer risk for Dutch population and ii) a cost-comparison between the health care provision for lung cancer and As removal from water to avoid lung cancer” [ 308 ]. The average concentrations of As in raw water from 241 public supply well fields in the Netherlands ranges from <0.5 μg/L to 69 μg/L; the treatment of this water to <1 μg/L saves the Netherlands from 7.2 million Euros (M€)/year to 14 M€/year [ 310 ]. This 7.2 M€/year to 14 M€/year includes the savings in health care costs from not having to treat excess lung cancer cases and the engineering costs from treating drinking water [ 308 ].

In the Netherlands, As is typically removed from raw well water by an optimized aeration and rapid sand filtration process [ 308 ]. This aeration oxidizes the soluble Fe(II) and As(III) that is naturally found in raw well water to insoluble Fe(III) and As(V) [ 308 ]. A soluble Fe(III) coagulant, such as FeCl 3 , is sometimes added to the raw well water [ 308 ]. This produces As-Fe(III) precipitates that are removed in a rapid sand filter [ 308 ]. This sand filter sometimes uses a coarse granular top layer and finer bottom layer [ 308 ]. This optimized process routinely removes As to <1 μg/L [ 308 ].

An optimized reverse osmosis process can also economically remove As from drinking water to concentrations that are significantly lower than 10 μg/L [ 309 ]. This process uses a 2-stage membrane cascade and can supply drinking water at 0.5 μg of As/L to a population of 20,000 people for US $1,041/day or US $0.52/m 3 [ 309 ]. A 2-stage membrane cascade has 2 reverse osmosis units connected in series. The feed water enters the first stage, the retentate or reject water from the first stage is discarded, and the permeate from the first stage enters the second stage. The retentate from the second stage is added to the feed water of the first stage. The permeate from the second stage is disinfected and distributed as drinking water. This process uses polyamide membranes [ 309 ]. The most significant cost is energy consumption; it is 35% of the total cost [ 309 ].

In summary, no country needs to use the less protective 10 μg/L standard or guideline due to limitations of treatment technologies. There are many treatment methods for reducing total As concentrations to lower more protective concentrations ( Table 5 ).

3.7 Implementation of regulations

Unfortunately, having legal standards for drinking water quality does not guarantee that these standards will be implemented, or that efforts will be made by suppliers to meet those standards, especially in regions where government and resources are limited. Implementation of standards can also be complicated when multiple jurisdictions are involved [ 310 ]. Transparency is vital for the effectiveness of guidelines and standards to protect public health [ 310 ]. In countries where standards bureaus control drinking water standards and release them only for a fee, transparency is severely curtailed. Compliance requires additional efforts and resources.

In contrast, in regions where government is effective and resources are sufficient, such as in Denmark and the Netherlands, reducing the national drinking water standard for As to below 5 μg/L in was found to be both technically feasible and affordable [ 248 , 311 ]. Even in regions in which there are limited resources for implementation and compliance, establishing and updating drinking water standards and guidelines can be of use to stakeholders who need to determine whether a water source is safe, and to put pressure on water suppliers to improve the quality of the water [ 311 ].

4. Conclusions

As demonstrated in this study, national and international guidelines and standards for As in drinking water need to be updated in accordance with current research and technologies. Updating regulations has the potential to improve public health by reducing As exposures worldwide. Technologies are now available that could enable both resource-limited and high income countries to adopt more protective drinking water regulations for As.

The WHO 10 μg/L drinking water guideline for As is provisional because it does not sufficiently protect public health. The value of 10 μg/L was specified on the basis of “analytical achievability” or “treatment performance” [ 17 , 18 , 132 , 272 ]. However, since the value for this guideline of 10 μg/L for was selected by the WHO in 1993, numerous new technologies and methods have been developed so that 10 μg/L no longer represents a practical limit for either analytical achievability or As treatment performance. This global drinking water guideline should be updated to better protect public health.

Many countries, especially lower income countries continue to use the long-outdated (1963) former WHO standard of 50 μg/L as a maximum allowable concentration for As [ 16 ]. Because many of these countries also have high populations, nearly one third of the world’s population lives in jurisdictions with a 50 μg/L standard for As. This concentration of 50 μg/L is associated with high levels of morbidity and mortality and can no longer be justified by the high cost of As quantification or treatment since new low-cost analytical and treatment methods are now available. Lowering the maximum allowable concentration from 50 μg/L to 10 μg/L or lower is urgently needed to avoid countless preventable cancer deaths and to better protect public health.

A variety of solutions are required to update and set more protective national drinking water standards and guidelines for As. In fact, each country might set a hierarchy of drinking water standards and guidelines for As. For example, low-income countries with limited resources might need to rely on relatively inexpensive spectrophotometers for testing and relatively simple systems for treating drinking water. If such a country or parts of a country had As-free water (Figs ​ (Figs2 2 and ​ and3), 3 ), then a 50 μg/L standard based on analytical achievability could be lowered to a more protective 0.3 μg/L standard through simple testing and water sharing ( Table 2 ). This would lower the lifetime cancer risk from 12,000 excess cancer deaths in 1,000,000 people (1 excess cancer death in 81 people) to 74 excess cancer deaths in 1,000,000 people (1 excess cancer death in 13,000 people; see Table 2 ). If such a country or parts of the country did not have As-free water (Figs ​ (Figs2 2 and ​ and3), 3 ), then a 50 μg/L standard based on “treatment performance” could be lowered to a more protective <5 μg/L standard through treatment ( Table 3 ). This would lower the lifetime cancer risk from 12,000 excess cancer deaths in 1,000,000 people (1 excess cancer death in 81 people) to <1,200 excess cancer deaths in 1,000,000 people (<1 excess cancer death in 810 people; see Table 3 ).

Countries with greater economic resources have access to more expensive instruments for testing and relatively sophisticated systems for treating drinking water. If such a country or parts of the country had As-free water (Figs ​ (Figs2 2 and ​ and3), 3 ), then a 10 μg/L standard based on analytical achievability could be lowered to a more protective ≤0.004 μg/L standard through testing and selective water use ( Table 4 ). This would lower the lifetime cancer risk from 2,500 excess cancer deaths in 1,000,000 people (1 excess cancer death in 400 people) to ≤1 excess cancer deaths in 1,000,000 people ( Table 4 ). If such country or parts of the country did not have As-free water (Figs ​ (Figs2 2 and ​ and3), 3 ), then a 10 μg/L standard based on treatment performance to a more protective 0.5 μg/L standard through more complete As treatment ( Table 5 ). This would lower the lifetime cancer risk from 2,500 excess cancer deaths in 1,000,000 people (1 excess cancer death in 400 people) to 120 excess cancer deaths in 1,000,000 people (1 excess cancer death in 8,100 people; see Table 5 ).

Supporting information

Acknowledgments.

We are grateful to Leif Rasmussen, Esq. for his assistance with international law. We are also grateful to Susan Murcott and Prakriti Sardana for their assistance reviewing this manuscript and to Mohammad Yusuf Siddiq for help translating Arabic documents.

Funding Statement

SHF received support for this project from the Norwich University Board of Fellows Faculty Development Prize. There is no grant number for this support. The Board of Fellows had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability

• PLoS One. 2022; 17(4): e0263505.

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Additional Editor Comments:

The manuscript submitted has merit in the field and serves as an excellent reference of current situations globally with respect to Arsenic exposures and the story leading us to where we are today. I do think there should be some substantive revisions of sections brought up by reviews, but the overall content of the manuscript remains sounds. Thank you for your submission!

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #1: Yes

Reviewer #2: No

2. Has the statistical analysis been performed appropriately and rigorously?

3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #2: Yes

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Reviewer #1: the title of a project are compatible with their work results, and the idea of the project is very crucial, in particular, the effects of Arsenic element on public health, and the WHO always promote the researchers to focus that kind of study

Reviewer #2: Arsenic in drinking water: an analysis of global drinking water regulations and recommendations for updates to protect public health

Comments for the authors

In this study, the authors collated and analyzed all drinking water regulations for As from national governments worldwide and related them with the health risks. The data was not interpreted scientifically. The presentation of the data is poor.

Abstract: The authors have only mentioned the data collection and analysis. what is the purpose of the study? what are the recommendations from this study.? Please revise the abstract.

Please revise the very first statement of the introduction ‘…that is often found in groundwater wells’

226,000,000 people… 226 million people

many low-and middle-income countries still use the World Health Organization’s (WHO’s) 1963 drinking water standard... I don’t agree with this assumption. From the previous few decades, groundwater As has gained considerable attention and most of the literature data present the comparison with WHO 10 µg/L.

I think the authors should pay more attention to the regulation limits. The Department of Environmental Protection for New Jersey has proposed the As limit of 5 µg/L in drinking water.

There are several other threshold limits from different areas that are not mentioned in this review.

Moreover, these regulation limits are made depending on the hydrogeochemistry of the specific region. Depending on the exposure scenario, the health risk indices and threshold guidelines are formed. The authors completely missed this type of useful information.

Section 2: It seems like the authors have collected data only from US states. Please clarify.

Section 2.1: I suggest avoiding the use of authorial (we or I). The use of passive voice can be suitable.

This study is more like a meta-analysis review. The authors have collected abundant data and categorized it according to the threshold value, income, health, etc. I question the robustness of statistics.

Which software was used to extract values of the data plotted in a graph? The authors did not follow guidelines of the analysis used in societies in academic fields.

The authors actually used very simple calculations based on simple empirical equations (just simple calculations with Excel). Though they provided those values, I do not think it has much meaning and much scientific advancement.

I think they just collected data but did not interpret it in a mechanistic way.

Section 3.4: All of the data processing and calculation should be mentioned under the methodology section.

Section 3.5: the section seems totally irrelevant to the current study. how can you relate this section with the data collected from various studies? Did the authors categorize the analysis techniques also…??? Even the developing countries have advanced methods of As analysis.

Section 3.5.2: We can not start any new section with ‘for example’…example of what?

Table 2: how the data was verified. The consumption of As-contaminated water could not be the only reason for developing cancer.

It is ambiguous to relate the cancer data with instrument detection limits.

The conclusion is simply a summary of the results. What is the take-home message of this study?

All the figure captions and indications are wrongly mentioned in the manuscript.

The figures related to the structure of the dyes or molecules seem irrelevant to the study.

There are several grammatical and punctuation mistakes in the manuscript.

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Reviewer #1: No

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Author response to Decision Letter 0

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The references to K&L Gates Law Firm, Minter Ellison Law Firm are likely for another manuscript. We have never heard of these firms and we do not have an author with the initials TPH. We do not have any commercial funders so we believe that we do not need to amend our Competing Interests Statement.

No changes made.

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All data are included in the supplementary file “supplementary file s1.xlsx”. This file is referenced with its caption on the very last line of our document, immediately following the References section.

3. We note that Figures 4 and 5 in your submission contain map images which may be copyrighted. All PLOS content is published under the Creative Commons Attribution License (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For these reasons, we cannot publish previously copyrighted maps or satellite images created using proprietary data, such as Google software (Google Maps, Street View, and Earth). For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright .

A. You may seek permission from the original copyright holder of Figure 4 and 5 to publish the content specifically under the CC BY 4.0 license.

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We created the maps in Figures 4 and 5 ourselves using the ggmap package in R. As requested in the reference document for the ggmap package ( https://cran.r-project.org/web/packages/ggmap/citation.html ), we have cited the authors of the ggmap package (Kahle and Wickham, 2013) since they provided the source code for the base maps on a CC by 4.0 basis. The ggmap source code was based on the public domain Natural Earth project. The figure captions of our maps cite Kahle and Wickham, 2013 as reference [264] as the source for these maps. These maps were not made with any copyrighted materials and they are suitable for CC by 4.0 licensing as is. We revised Section 2.2 (Data analysis and statistics) to explicitly state that we created the maps in R with the ggmaps package.

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The caption for our Supporting Information file appears on the very last line of our document, immediately following the References section.

We have reviewed the reference list and it is complete and correct. We have not cited any retracted papers. We have fixed several typos and added missing doi links where needed. We deleted two references in response to reviewer comments and renumbered subsequent references.

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Thank you for reading the manuscript carefully and soliciting helpful reviewer comments. This was a monumental effort, and we are grateful that our research will be made available with the publication of this paper for others to use.

Reviewer #1: Yes

Reviewer #2: No

________________________________________

Reviewer #2: Yes

Reviewer #1: the title of a project are compatible with their work results, and the idea of the project is very crucial, in particular, the effects of Arsenic element on public health, and the WHO always promote the researchers to focus that kind of study

Reviewer #2: Arsenic in drinking water: an analysis of global drinking water regulations and recommendations for updates to protect public health

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We have revised the abstract to state the purpose and recommendations of the study more explicitly.

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many low-and middle-income countries still use the World Health Organization’s (WHO’s) 1963 drinking water standard... I don’t agree with this assumption.

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Please note that this is not an assumption. It is a fact that is directly supported by the data that we collated for this study. See our data in Table 1 that show that as of 2021, 36 countries still use the WHO’s 1963 drinking water standard. All but 2 of these countries are classified as low or middle income by the World Bank. As mentioned in the Abstract, the percentage of population living in countries that do not meet the current WHO drinking water guideline for As constitutes 32% of the total global population.

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From the previous few decades, groundwater As has gained considerable attention and most of the literature data present the comparison with WHO 10 µg/L.

It is fortunate that most studies in the literature use the current WHO 10 µg/L guideline for comparison. However, many countries still legally use the former 1963 WHO guideline, as shown in Table 1 and explained in our previous response.

The title of this paper is “Arsenic in drinking water: an analysis of global drinking water regulations and recommendations for updates to protect public health.”. This paper focuses on national regulations, not the regulations of individual states, provinces, districts, etc. within any one nation such as the United States. Thus, we do not cover regulations for the individual states of the United States. We do cover As regulations for every national government in the world that we could locate in our extensive search for national regulations.

As discussed in our Abstract, Introduction, and Section 3.3 (The drinking water guideline set by the World Health Organization), the World Health Organization’s (WHO’s) drinking water guidelines take into account health risk assessments, analytical capabilities, and treatment performance. The WHO guidelines are not based on hydrogeochemistry. More specifically, the 1963 WHO drinking water standard for As of 50 micrograms per liter (µg/L) was based entirely on “analytical achievability”. Similarly, the WHO’s 10 µg/L guideline established in 1993 was also based entirely on “analytical achievability”; however, in 2011 the additional proviso of “treatment performance” was added to the current WHO WHO’s 10 µg/L guideline. The WHO also states that these values cause an unacceptable risk of death from “skin and possibly other cancers” and cannot be set at a lower, more protective health-based level because it cannot be measured in a routine testing laboratory or removed by conventional treatment plants.

Furthermore, in Section 3.3, we wrote “National regulators are encouraged [by the WHO] to take local conditions, resources, and hazards into account when setting national standards [268,269].” We cited the WHO’s 2018 document “Developing drinking-water quality regulations” [our reference 269] in support of this statement.

The title of this paper is “Arsenic in drinking water: an analysis of global drinking water regulations and recommendations for updates to protect public health”. There is no suggestion in the title that any regulations from individual US states will be discussed, nor is there any survey of data from US states.

The title of our Section 2.1 is “International drinking water standards for arsenic”. As detailed in the first 2 sentences of that section, the entries in the database that we created and present in Table 1 include the 193 United Nations member states plus Taiwan and Kosovo. Individual US state regulations were not part of this database.

Although PLOS does not have explicit advice regarding passive or active voice, many other leading publishers such as Sage Journals ( https://journals.sagepub.com/author-instructions/phr ), Cambridge University Press ( https://www.cambridge.org/core/journals/enterprise-and-society/information/instructions-contributors ), NatureProtocols ( https://www.nature.com/nprot/for-authors/preparing-your-submission ), and the Canadian Medical Association Journal ( https://www.cmaj.ca/submission-guidelines ) all explicitly recommend or require active voice rather than passive voice. We have not encountered any scientific journals that require passive voice to avoid agency. Thus, we believe it is acceptable to use active voice in scientific writing.

Which software was used to extract values of the data plotted in a graph?

As stated in Section 2.2 (Data analysis and statistics), we used R version 4.1.1 for all statistics and data analysis. All of the figures and maps were also made with R. We added a sentence to the end of Section 2.2 to explicitly state that we used R to create the figures and maps as well as to perform the statistical analyses.

The authors did not follow guidelines of the analysis used in societies in academic fields.

As noted in Section 2.2 (Data analysis and statistics), we used R for the statistical calculations, not Excel. We believe our use of statistics is in accordance with standard practices for scientific writing. After comparing our reporting of statistics to the PLOS guidelines ( https://journals.plos.org/plosone/s/submission-guidelines.#loc-statistical-reporting ), to be fully in compliance, we added a statement to Section 2.2 about why we did not use corrections for multiple comparisons. That is, we did not use corrections for multiple comparisons in this paper because we did not make multiple statistical comparisons of the data.

As noted in Sections 3.1 and 3.2, this study is the most comprehensive study of national drinking water regulations for arsenic that has ever been published to date. It provides and analyses data for almost twice as many countries (195) as a 2018 WHO survey (104 countries). As a result, our Table 1 and the references cited in the table constitute the most complete database of national drinking water regulations published to date. By virtue of its completeness of scope, this study provides comparative information about the drinking water regulations for arsenic worldwide that has never been available before.

The statistical analyses of this data set provide the first firm data concerning the relationship between the protectiveness of national regulations for arsenic in drinking water and national per capita income. More specifically, “the GDPs per capita of countries with As regulations equal to or more protective than the WHO of guideline of 10 µg/L were significantly higher (n = 129, M = $17,678) than those of countries with As regulations less protective than the current 10 µg/L WHO guideline (n = 36, M = $5,384) (F(2,177) = 7.55, p<.001)”. It also shows that the recency of regulations is not related to national per capita income. An extremely important finding of this study is that nearly 1/3 of the world’s population live in jurisdictions that still use the 1963 WHO standard of 50 μg As/L as their national standard. We believe these findings are crucial for understanding the relationship between regulations and risks to public health, and that they are critical for directing future efforts to protect health.

This Section, (3.4 Health-based drinking water guidelines) of the Results and Discussion section, provides discussion of several regulatory documents and their implications for public health. The equations in this section were not part of our research on current international drinking water regulations, so it is not appropriate to discuss the calculations in the Materials and Methods section, which describes the materials and methods for our collation of international drinking water regulations and their analysis.

The equations are provided here for completeness and transparency to demonstrate the implications of regulations that are based on “analytical achievability”, “treatment performance”, the risk of death from various cancers, and public health. This is essential for the following discussion on various tangible ways to reduce the risk of death from cancer and protect public health.

As stressed in Section 4 (Conclusions), our overarching recommendation is that international guidelines and national standards for As in drinking water are out of date and need to be updated in accordance with the advances of science.

In Section 3.2 (Arsenic regulations, population, and per capita income), we showed that many countries, especially low and medium income countries, still use the 1963 WHO standard of 50 μg As/L as their national standards. This standard is based on analytical achievability from 58 years ago. In Section 3.5 (Low-cost methods for improving public health by reducing arsenic exposure), we enumerate examples of currently available low-cost methods for analysis and treatment of As contaminated water. This enumeration is an essential step for our argument that it is feasible for low and middle income countries to adopt more stringent standards regarding As in drinking water. Again, approximately one-third of the global population live in countries that do not meet the current 10 µg/L WHO drinking water guideline for As. We believe that reducing the income inequities in international drinking water regulations would be a positive step towards reducing the global health gap for lower income people.

We have reworded this sentence for clarity.

Table 2: how the data was verified.

The comparison figures in the 2 right-hand columns of Table 2 are drawn from equations 1-6, as stated in the table caption. As described in detail in Section 3.4 (Health-based drinking water guidelines), these equations and estimates of cancer deaths are drawn directly from published regulatory documents, for which we provide citations in Section 3.4.

The consumption of As-contaminated water could not be the only reason for developing cancer.

It is quite correct that “The consumption of As-contaminated water could not be the only reason for developing cancer”. This is why regulators rely on the concept of “Excess cancer deaths”, a common metric in risk assessment used for calculating health-based drinking water quality guidelines and standards. We revised our description of excess cancer deaths in Section 3.4 (Health-based drinking water guidelines) to clarify this point.

The purpose of Table 2 is to facilitate direct comparisons between regulatory limits, detection limits, and regulatory risk assessments. We believe these comparisons will be useful for prioritizing efforts to protect public health.

We have added a new paragraph to Section 4 (Conclusions) to state our take-home message more explicitly.

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We have checked the figure captions and in-text citations and verified that they are in fully in compliance with PLOS guidelines ( https://journals.plos.org/plosone/s/figures ). Two figures were numbered incorrectly; they have been deleted in accordance with the following comment.

We have deleted these figures and their associated citations.

Thank you for this observation. We have proofread the document again and fixed several typographical, grammar, and punctuation errors.

Decision Letter 1

21 Jan 2022

Arsenic in drinking water: an analysis of global drinking water regulations and recommendations for updates to protect public health

PONE-D-21-35059R1

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Acceptance letter

11 Mar 2022

Dear Dr. Frisbie:

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Review of analytical techniques for arsenic detection and determination in drinking water

First published on 7th November 2022

Arsenic occurs in the natural environment in four oxidation states: As( V ), As( III ), As(0) and As(− III ). The behavior of arsenic species changes depending on the biotic or abiotic conditions in water. In groundwater, arsenic is predominantly present as As( III ) and As( V ), with a minor amount of methyl and dimethyl arsenic compounds being reported. Global intake of As( III ) and As( V ) via drinking water and food has dramatically increased in recent years. The commonly used term inorganic arsenic includes both As( III ) and As( V ) species and constitutes the highest toxicological risk associated with arsenic in water compared to the organic arsenic species. Inorganic arsenic is a confirmed carcinogen and the World Health Organization (WHO) has published a guideline value for arsenic in their ‘Guidelines for drinking-water quality’ and is on the WHO list of 10 chemicals of major public health concern. Presently, approximately, 230 million people worldwide are affected by arsenic toxicity. Chronic arsenic toxicity affects multiple physiological systems and can cause serious health issues ( e.g. arsenicosis, cancer etc. ) leading to death. To combat arsenic pollution, the WHO and United States Environmental Protection Agency (US-EPA) have set concentration limits for arsenic in drinking water. The WHO, US-EPA and European Union (EU) have set the maximum limit of arsenic in drinking water at 10 ppb. To meet the required limit, it is essential that rapid, reliable, sensitive and cost-effective analytical detection systems be developed and put into use. Different determination methods of inorganic arsenic have been developed over the last 5–6 decades. This review provides an overview of around 170 research articles and relevant literature, mainly regarding the existing methods for analysis of As( III ) and As( V ) in water. Chromatographic, spectroscopic, colorimetric, biological (whole cell biosensors (WCB) and aptasensors), electroanalytical and coupled techniques are discussed. For those who are at the early stage of their research career in this field, the basic introduction and necessary concepts for various techniques is discussed followed by an evaluation of their performance towards arsenic determination. Current challenges as well as potential avenues for future research, including the demands for enhanced analytical performance, rapid analysis and on-site technologies for remote water analysis and environmental applications are discussed. We believe that this review will be beneficial, a source of information, and enhance awareness and appreciation of the role of these advanced analytical techniques in informing and protecting our environment and water resources, globally.

1. Introduction

Arsenic exists in four oxidation states in nature: As( V ), As( III ), As(0), and As(− III ) ( Fig. 2 ). The behavior of arsenic species changes depending on the biotic or abiotic conditions in water. In groundwater, arsenic is predominantly present as As( III ) and As( V ), with a minor amount of methyl and dimethyl arsenic compounds being reported. 3 The term inorganic arsenic includes both As( III ) and As( V ) species and constitutes the highest toxicological risk associated with arsenic in water in contrast to the organic arsenic species. The WHO has published a guideline value for arsenic in its Guidelines for drinking-water quality and arsenic is on their list of 10 chemicals of major public health concern. 4 Presently, more than 230 million people worldwide are affected by arsenic toxicity. 5 Acute arsenic toxicity has been reported to cause acute paralytic syndrome (APS) and acute gastrointestinal syndrome (AGS). 6 Chronic arsenic toxicity affects multiple physiological systems and can cause serious health issues e.g. black-foot illnesses, arsenicosis, cancer, etc. Numerous epidemiological studies have examined the risk of cancers associated with the arsenic absorption through drinking water. There is significant evidence that greater arsenic levels in drinking water are linked to cancer growth including the skin, bladder, and lungs related cancers. The International Agency for Research on Cancer (IARC) classified arsenic and inorganic arsenic as “carcinogenic to humans” (group 1). 7

To combat arsenic pollution and associated toxicity, the WHO, US-EPA and EU have guidelines, regulations and directives that set concentration limits for arsenic in drinking, surface and ground water. Also, due to the toxic potential of inorganic As, the European Food Safety Authority (EFSA) recommends minimizing its intake and the European Commission has set the maximum levels. 7 WHO, EU and US-EPA maximum limit for arsenic in drinking water is 10 ppb. 8,9 To meet this value, it is essential that rapid, sensitive, cost-effective and reliable analytical detection systems be developed and put into use.

Determination of arsenic species is of crucial importance to define the limits and safety of drinking water as well as in selection of arsenic removal technology for groundwater applications. The importance of arsenic determination is well-recognised and emphasised by the extensive studies carried out in this space e.g. “Arsenic round the world: a review”. 7,10 A plethora of detection methods have been developed and reported and some are capable of detecting arsenic below the WHO guideline value of 10 ppb ( Fig. 3 ). 11,12 The most selective and sensitive methods for determination of total arsenic and its species in water are coupled techniques including chromatography, optical methods and mass spectrometry. 2,11,12 Coupled techniques are where combined methods e.g. chromatographic and spectroscopic are used to determine arsenic levels. Colorimetric, biological, electrochemical techniques have also been reported for the arsenic determination. 13–17 Most of the existing methods are suitable for laboratory conditions only and analysis is time consuming and can lead to a large capital cost for multi-sample analysis hence not suitable for routine monitoring of large numbers of samples. Therefore, rapid, cost-effective, reliable and portable techniques such as on-site sensor-based methods are crucial. In this regard, the use of electrochemical methodologies has recently come to the forefront of research as a possible means of fulfilling these requirements.

The purpose of this review is to provide an overview of the analytical techniques (chromatographic, spectroscopic, colorimetric, biological, electroanalytical and coupled techniques) for arsenic determination in drinking water and the authors have mostly covered the literature over the past decade (2010 onwards). Some older publications are referenced to support the key concepts and wherever necessary. A brief introduction to various analytical techniques followed by an evaluation of their capabilities and performance for arsenic determination are discussed. Associated challenges as well as potential avenues for future research, including the demand for rapid analysis and on-site technologies for remote water analysis and environmental applications are discussed. We hope that this review will be of benefit to those working in the area of water and environmental analysis in particular to the postgraduate students, early-stage researchers and scientists. Overall, this review will enhance awareness and appreciation of the role that these advanced analytical techniques play in informing and protecting our environment and water resources, globally.

2. Analytical methods & techniques for arsenic determination

2.1. spectroscopic methods.

2.2. Chromatographic methods & hyphenated techniques

However, SEC is very effective for analysis of arsenic interactions with large molecules. For instance, analysis of arsenic–protein binding commonly uses SEC to separate protein-bound arsenic from free arsenic. 12 García-Sevillano et al. used SEC to measure arsenic–biomolecule complexes from liver extracts of Mus musculus . 51 Chen et al. used SEC to separate and collect protein-bound arsenic from free arsenic, followed by hydrogen peroxide treatment to release the protein-bound arsenic. 52 Schmidt et al. simultaneously measured binding of phenylarsine oxide to five different peptides and proteins (glutathione, oxytocin, aprotinin, α-lactalbumin, thioredoxin) using SEC-ESI-MS. 53 Yang et al. investigated the roles of dissolved organic matter on arsenic mobilisation and speciation in environmental water using (SEC), combined with (ICP-MS), as well as three-dimensional excitation–emission matrix (3DEEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). Low LODs (0.014–0.041 ppb) were reported. 54 The relevant literature on the chromatographic technique is summarised in the Table 2 .

Hyphenated techniques have become more popular in recent times. Chromatographic methods such as liquid chromatography offer excellent possibility for the separation of all arsenic species because a variety of separation modes can be employed, followed by detection with different detection techniques, particularly in HPLC coupled in hyphenated techniques such as HPLC-hydride generation atomic absorption spectrometry (HG–AAS), hydride generation atomic emission spectrometry (HG-AES) and HPLC-ICP-MS. These methods are successfully and extensively used for the determination of the arsenic species at trace levels in environmental samples because of their low LODs.

HPLC methods for arsenic speciation are based on reversed phase chromatography with, usually, phosphate buffered mobile phases. This is relatively easy to set up, reasonably sensitive and provides the necessary chromatographic resolution of the target species. However, the need for a buffered, sometimes multi-component mobile phase leads to extra preparation work and more cost. In addition, the presence of phosphate in the mobile phase is not ideal for the ICP-MS instrument, as phosphates cause pitting of the interface cones, leading to more frequent replacement or necessitating the use of more robust (and much more expensive) Pt-tipped cones. Longer term operation of HPLC methods for arsenic speciation eventually leads to a drop off in sensitivity and peak retention time drift caused by other components in the sample, leading to the need to periodically change the HPLC column. For lower numbers of samples, HPLC is a cost-effective solution, but the less expensive instrument cost can eventually be offset by the higher column consumable costs in the longer term. 42 In contrast, IC offers the benefits of sharp peak shapes (even for late eluting species), retention time stability, column robustness, excellent long-term peak area/height reproducibility and simpler mobile phases; only dilute ammonium carbonate is required, which is easy to prepare. In addition, dilute ammonium carbonate is fully converted to gaseous species in the plasma (NO 2 , H 2 O and CO 2 ), so no damage or blocking of the interface cones occurs when using this mobile phase. Although not so much of an issue for arsenic speciation, IC also provides a metal-free sample path as standard, which provides lower backgrounds for other elements of speciation interest, such as chromium. Although IC instruments can be more expensive to purchase than HPLC systems, over time this can be offset by the lower consumables cost. Ponthieu et al. proposed a cation exchange IC-ICP-MS method for the simultaneous determination of eight arsenic species using mobile phases prepared from ammonium nitrate. 58 The relevant literature on the coupled/hyphenated chromatographic technique is summarised in the Table 3 .

2.3. Colorimetric methods

To avoid human bias, digital colour processing can replace semi-quantification by visual comparison with a colour chart. Such an idea was adopted by a number of commercial products, for instances, the Arsenator by Wagtech and the DigiPAsS by Palintest. Parts used to remove interfering gas, such as hydrogen sulphide, are included in modern kits. A recent evaluation of 8 commercial arsenic field test kits for drinking water (Bangladesh) by comparing with HG-AAS showed a performance correlation with the product price. The two most expensive kits, LaMotte and Quick II kit, provided the best estimates while the cheapest were neither accurate nor precise. 78

Some of the relevant literature on the colorimetric arsenic detection technique is summarised in the Table 5 .

According to authors, the results reflect that different arsenic contamination produces different intensities of colour, thereby can be used to distinguish between different arsenic percentages. However, the method may not be fully reliable as it depends on visual colour comparison. 15

Silver nanoparticles (AgNPs) are reported to provide a rapid response to localised surface plasmon resonance compared to gold nanoparticles with enhanced sensitivity. 85 Polyethylene glycol (PEG)-functionalised silver nanoparticles are well-suited for detecting arsenic( III ) ions in an aqueous medium. 86 The PEG-modified silver nanoparticles are sufficient enough to detect arsenic( III ) in 1 ppb due to the addition of PEG. PEG-functionalised AgNPs have adjustable negative surface charges, responsible for the nanoparticle's stability and the electrostatic repulsion between negatively charged surfaces of AgNPs protects them from agglomeration. Interestingly, in the presence of As( III ), the functional AgNPs interacted with PEG hydroxyl groups, which led to the aggregation of AgNPs. As a result, the colour of functionalised nanoparticles changed from yellow to bluish ( Fig. 6 ). A silver nanoprisms (AgNPr) based assay has been designed and reported to achieve the wide range morphologically modified surface plasmon tuning–detuning for accurate colour-coded detection and sensing of As( III ) over other alkali, alkaline, and transition metals ( Fig. 7 ). 87 Plasmon tuning–detuning not only confirms the presence but also can detect As( III ) concentration up to a limit of 75 ppb. The authors have suggested that the assays ability to detect As( III ) in real water samples coupled with its cost effectiveness make it potentially useful for field applications. 87

2.4. Biological methods

Biological detection methods developed for arsenic have mostly been based on the ars operon. An operon is a cluster of genes which are transcribed together giving a single messenger RNA (mRNA) molecule that encodes for multiple proteins. 92 Plasmid encoded ars operons found in bacterial species such as E . coli are known to confer a certain level of resistance to As( III ) and As( V ) through giving cells the ability to remove As species from within the cell, lowering the intracellular concentration of toxic arsenic species. 93 Upon encountering arsenite, a dedicated sensory protein in the bacterial cell called ArsR will undergo a conformational change that unleashes expression of the defence system. 94 This protein functions as a transcriptional repressor, attaching to a particular DNA sequence (the operator) that overlaps the binding site for RNA polymerase in the absence of arsenic (the promoter). However, when binding arsenite, ArsR will lose its affinity for the DNA and RNA polymerase can start transcription. 94 This detoxification system can be exploited for highly specific and sensitive arsenic detection. Modifications involve the coupling of the regulatory elements of the ars operon, including the transcriptional regulator and cognate promoters to reporter genes for Green fluorescent protein (GFP), luciferase, and β-galactosidase (lacZ). In response to the presence of arsenic, genetically modified bacterial species such E. coli , Bacillus subtilis , Staphylococcus aureus , and Rhodopseudomonas palustris , generate reporter proteins, the amount or activity of which is related to arsenic concentration. Such an approach has allowed for LODs in the order of 1 ppb. E. Diesel et al. ( Fig. 8 ) summarised the use of bacteria-based assays as an emerging method that is both robust and inexpensive for the detection of arsenic in groundwater for both in the field and laboratory. 95

Kaur et al. mentioned that the development of whole cell biosensors employing these metabolic processes for their design. 96 In case of arsenic, the well-established ability of As( III ) or As( V ) to bind the ArsR protein and undo its repressor function on the Ars promoter leads to subsequent synthesis of reporter genes. Thus, whole-cell-based biosensors devised using the above approach have been further subdivided, based on their signal transduction mechanisms like luciferase, lacZ and GFP whereby the signal relay is either in terms of fluorescence, luminescence or colorimetry as depicted in Fig. 9A . 96 Wang et al. developed a convenient analysis method for environmental monitoring, that intended to employ in vitro protein expression technology to detect toxic pollutants based on evolved genetically encoded biosensors ( Fig. 9B ). His team established a genetically encoded biosensor in vitro with ArsR and GFP reporter gene. Given that the wildtype ArsR did not respond to arsenic and activate GFP expression in vitro , they found, after screening, an evolved ArsR mutant ep3 could respond to arsenic and exhibited an approximately 3.4-fold fluorescence increase. 97

The engineered promoter modification approach is used to improve the performance of whole-cell biosensors to facilitate their practical application. A recent study, demonstrated how to design the core elements ( i.e. , RNA polymerase binding site and transcription factor binding site) of the promoters to obtain a significant gain in the signal-to-noise output ratio of the whole-cell biosensor circuits ( Fig. 10 , left). 88 The arsenite-regulated promoter from Escherichia coli K-12 genome was modified to lower background and higher expression and was achieved by balancing the relationship between the number of ArsR binding sites (ABS) and the activity of the promoter and adjusting the location of the auxiliary ABS. A promoter variant ParsD-ABS-8 was obtained with an induction ratio of 179 when induced with 1 μM arsenite (11-fold increase over the wild-type promoter). The reported biosensor exhibited good dose–response in the range of 0.1 to 4 μM ( R 2 = 0.9928) of arsenite with a detection limit of ca. 10 nM.

An arsenic WCB with a positive feedback amplifier Escherichia coli DH5α was developed and reported ( Fig. 10 , right), 98 where the output signal from the reporter mCherry was significantly enhanced by the positive feedback amplifier. The sensitivity of the WCB with positive feedback was about 1 order of magnitude higher compared to without positive feedback when evaluated using a half As( III ) concentration (half-saturation). The LOD for As( III ) was reduced by 1 order of magnitude to 0.1 μM, lower than the WHO standard for the arsenic levels in drinking water (0.13 μM). The WCB with the positive feedback amplifier exhibited exceptionally high specificity toward As( III ) when compared with other metal ions. The importance of genetic circuit engineering in designing WCBs, and the use of genetic positive feedback amplifiers may be a good strategy to improve the performance of WCBs. The integration of WCBs for the field-ready electrochemical detection of arsenic (FRED-As) has been reported recently. 99 Sergio Sánchez et al. reported a WCB biosensor which was followed by electrochemical measurements and provided enhanced accuracy and signal intensity compared to traditional bacterial-detection approaches ( Fig. 11 ). FRED-As had a number of benefits including ease of use, potential for measuring a wide spectrum of metals, sensitivity etc. When integrated within a customised hardware system, the reported whole-cell biosensor demonstrated excellent specificity and sensitivity with an LOD 95% confidence, (FRED-As) of 2.2 ppb As( III ). 99 This sensitive and easy-to-use approach may be a viable alternative for on-site arsenic testing.

Ensafi et al. , have developed a CdTe/ZnS QDs (quantum dots) aggregation-based fluorimeter aptasensor for As( III ) ( Fig. 12C ). 103 The aptamer was designed to aggregate cationic cysteamine-stabilised CdTe/ZnS QDs, which led to fluorescence quenching. When As( III ) was introduced, the complex between the aptamer and As( III ) prevented aggregation of the QDs. Therefore, depending upon the As( III ) concentration, the QDs fluorescence was enhanced due to de-aggregation. The fluorescence analysis held a promising LOD of 1.3 pM with a dynamic range of 10 −2 to 10 3 nM. The proposed QDs based aptasensor has advantages such as high sensitivity and selectivity, compared with conventional dyes based aptasensors. Zhang et al. ( Fig. 12D ), reported an arsenite detection strategy based on the fluorescence enhancement of DNA QDs. 104 In their work, they synthesised DNA QDs using G/T-rich ssDNA that showed special optical properties, and acquired the basic structure and biological activities of ssDNA precursors, making the QDs selectively bind with arsenite, driving the (GT) 29 region towards conformational switching and form a well-ordered assembly. They speculated that the strong inter-molecular interaction and efficient stacking of base pairs stiffened the assembly structure, blocked non-radiative relaxation channels, populated radiative decay, and thus made the assembly highly emissive as a new fluorescence center. The fluorescence enhancement induced by arsenite promoted QDs as light-up probes for determination of arsenite. A very good linear relationship was demonstrated between fluorescence intensity and logarithmic arsenite concentration from 1–150 ppb with an LOD of 0.2 ppb reported.

The first colorimetric arsenic aptasensor was reported by Wu and co-workers ( Fig. 12E ). In the presence of Arsenic, the aptamer selectively interacted with As( III ) forming an As–aptamer complex. The formation of this complex allowed the cationic polymer poly-diallyldimethylammonium (PDDA) to aggregate AuNPs, resulting in an obvious colour variance allowing for highly sensitive colorimetric arsenic detection. 105 In the same year, Wu and co-workers reported another aptasensor employing a different polymer (cetyltrimethylammonium bromide, CTAB) that also utilised AuNP induced aggregation for As( III ) detection ( Fig. 12F ). The dynamic range spanned from 1–1500 ppb with the LOD of 0.6 ppb for colour analysis and 40 ppb for naked-eye detection, respectively. 106 Following the same strategy, Nguyen et al. developed a novel biosensor based on CTAB and AuNPs for colorimetric detection of As( III ) with an LOD of 16.9 ppb in real samples. 14 Zhou's group ( Fig. 12G ) reported the salt-induced aggregation of AuNPs (classical aptamer-based AuNPs colorimetric method) for As( III ) detection. 107 In this study, an arsenic aptamer was employed as the probe with AuNPs as a colorimetric signal. When As( III ) was absent in the solution, AuNPs were wrapped by aptamer and therefore stable even when a high concentration of sodium chloride was in the solution, showing a red colour. When introduced to As( III ), the AuNPs were easy to aggregate due to the formation of the As–aptamer complex, showing a blue coloured solution. Through monitoring the coluor variance, the rapid colorimetric detection methods for As( III ) with a dynamic range from 1.26 to 200 ppb and a LOD of 1.26 ppb was demonstrated. However, AuNPs-based biosensors are dependent on salt-induced aggregation, which seems to make them more susceptible to interference by environmental matrices. Natural matrices are typically diluted in a buffer before sensing, but matrices with high salt concentrations must be handled carefully when performing this assay.

Divsar et al. , (2015) 109 prepared AgNPs modified by aptamer (Apt–AgNPs) and used it for colorimetric determination of As( III ). In their work, As( III ) could selectively interact with Apt–AgNPs resulting in the formation of an As( III )–Apt–AgNPs complex and cause an obvious decrease in peak intensity ( λ max 403 nm), which was proportional to As( III ) concentration. Additionally, a combination of a central composite design optimisation method and response surface methodology was applied to optimize the efficiency of As( III ) analysis. The linear range of the colorimetric biosensor held a wide scope of As( III ) concentration from 50 to 700 ppb with a LOD of 6 ppb. Wu et al. reported the development of a colorimetric aptasensor for As( III ) determination that was designed through the combination of aptamer and G-quadruplex DNAzyme (Wu et al. Fig. 12H ). 108 The catalytic activity of hemin peroxidase was temporarily inhibited by As–aptamer complex. In the presence of As( III ) an As–aptamer complex formed allowing hemin peroxidase catalyze TMB oxidation in the presence of H 2 O 2 resulting in an obvious increase of UV-vis spectra intensity (442 nm), LOD of 6 ppb was reported.

Recently, a highly sensitive fluorescence sensing platform for As( III ) detection based on target-triggered successive signal amplification strategy was demonstrated. As( III ) aptamer was used as the recognition unit and in the presence of As( III ), the blocking DNA is released to trigger the cascade signal amplification process. The integration of Exo III-assisted DNA recycling and DNAzyme-based catalytic cleavage with multiple turnovers results in the generation of amplified fluorescence signals (significantly) for highly sensitive quantification of trace levels of As( III ), and a detection limit of 2 pM was achieved ( Fig. 13 ). 110

Some of the biological sensors with their performances are summarised in Table 6 .

2.5. Electrochemical methods

As mentioned above, electrode surface modification with metallic nanoparticles, carbonaceous nanomaterials ( e.g. carbon nanotubes, nanofibers and graphene) and even enzymes (arsenite oxidase) can improve detection sensitivity and selectivity, while circumventing interferences. Fig. 15 shows the schematic comparing the laboratory based electrochemical devices vs. portable electrochemical devices and classical electrodes vs. screen-printed electrodes. The commonly used materials (textile, paper based etc. ) and fabrication methods (inkjet, screen and 3D printing) are illustrated for the construction of flexible and wearable printed electrodes/sensors. 125 A low-cost plastic-based microfluidic arsenic sensor comprised of an ink-based three-electrode system used for rapid and point-of-use water quality monitoring. A water sample is applied to the sensing system and hand-held analyzer runs a voltammetric test on the sample to determine arsenic concentration. 126

Thakkar et al. made a detailed review of arsenic detection methodologies with LODs of <10 ppb (WHO guideline value). They have critically compared the methods in terms of their potential to detect different arsenic species e.g. As( III ) and As( V ) in drinking water in the presence of interference from other ions. 17 According to Duoc and colleagues, a novel electrochemical sensor containing double-walled carbon nanotubes (DWCNTs) and a graphene hybrid thin film was discussed for As( V ) detection. 128 The hybrid thin films based on DWCNTs and graphene have been prepared for electrochemical sensing applications. The hybrid films were synthesised on polycrystalline copper foil by thermal chemical vapor deposition under low pressure. This carbonaceous hybrid film has exhibited high transparency with a transmittance of 94.3%. The occurrence of this hybrid material on the electrode surface of screen-printed electrodes was found to increase electroactive surface area by 1.4 times, whereas electrochemical current was enhanced by 2.4 times. This highly transparent and conductive hybrid film was utilised as a transducing platform of an enzymatic electrochemical As( V ) biosensor and showed the linear range from 1–10 ppb, with an LOD as low as 0.287 ppb. 128

AuNPs–polyaniline nanosheet array on iron containing carbon nanofiber (Au–PANI–Fe–CNFs composite) was reported as sensing platform for the determination of As( III ). 129 The Au–PANI–Fe–CNFs composite was constructed by the formation of polyaniline (PANI) nanosheet array on the electrospun Fe-containing carbon nanofibers (Fe-CNFs) substrate and self-deposition of Au nanoparticles. PANI presents a uniform array structure on the fiber surfaces and Au nanoparticles (20 ± 6 nm) were deposited uniformly on the PANI nanosheet surface by means of the reducing property of PANI. The presence and role of Fe in the CNFs was mentioned to accelerate the growth of PANI nanosheet and improves the arsenic adsorption in the sensing process of As( III ). The Au–PANI–Fe–CNFs sensor exhibit excellent electrochemical performance for the detection of As( III ) in water (linear range 5–400 ppb with an LOD of 0.5 ppb, S/N ≥ 3) and attributed to the unique structure of PANI array and uniform AuNPs distribution. 129 According to Bu et al. , a new material of 3D porous graphitic carbon nitride (g-C 3 N 4 ) decorated by gold nanoparticles (AuNPs/g-C 3 N 4 ) was designed using a mesoporous molecular sieve (SBA-15) as the sacrificial template. 130 The reported AuNPs/g-C 3 N 4 /GCE electrode demonstrates superiorities compared to AuNPs/GCE prepared by electrochemical deposition, highlighting the specialties of g-C 3 N 4 in increasing activity and sensitivity with an extremely low LOD of 0.22 ppb. 130 Zhang and Compton recently reported the use of anodic stripping voltammetry (ASV) allowing sub 10 ppb measurement of total As and As( III ) in water using the gold macroelectrodes and based on the underpotential deposition (UPD) of As ad-atoms ( Fig. 16 ). 131 The detection of As( III ) or total arsenic can be selectively made by changing deposition potential (total As content by deposition at −1.3 V and As( III ) at −0.9 V, linear responses were observed in the range 0.01–0.1 μM). The analytical signals were recorded at concentrations as low as 0.01 μM (0.8 ppb) for both arsenic species which suggests that this method could be used to detect total arsenic concentrations in drinking water within the WHO threshold value of 10 ppb. The As( V ) concentration can be determined by subtraction from the total arsenic concentration of the As( III ) concentration.

3. Conclusion

This review provides an overview of existing methods for analysis of arsenic (mainly As( III ) and As( V )) in water. Various chromatographic, spectroscopic, colorimetric, biological, electroanalytical and coupled techniques were discussed followed by evaluation of their performances towards arsenic detection and determination. Relevant images and informative data are presented throughout the manuscript by reviewing the concerned literature for various analytical technique and methods. Current challenges as well as potential avenues for future research, including the demands for enhanced analytical performance, rapid analysis and on-site technologies for water analysis are discussed. Currently the coupled or hyphenated analytical techniques and methods ( e.g. ICP-MS, LC-MS, HPLC/ICP-MS) are the most promising and realistic way of arsenic determination but the novel and on-site methods based on biosensors, nanomaterials and electroanalytical or electronic devices are the future hopes for sensitive, rapid and cost-effective arsenic detection and determination. The use of novel materials, biomaterials and advanced functional nanomaterials (including metallic nanoparticles, graphene, carbon nanotubes, QDs and polymer-based nanocomposites) have the potential to improve the sensitivity, selectivity, biocompatibility and overall performance, and could open up new opportunities in the future arsenic analysis. Overall, this review will be beneficial and enhance awareness and appreciation of the role of analytical techniques in arsenic determination and in protecting our environment and water resources.

Author contributions

Conflicts of interest, acknowledgements.

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Home > Books > Arsenic - Analytical and Toxicological Studies

Arsenic in Water: Determination and Removal

Submitted: 21 November 2017 Reviewed: 16 February 2018 Published: 25 July 2018

DOI: 10.5772/intechopen.75531

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Depending on the physical, chemical and biogeochemical processes and condition of the environment, various arsenic species can be present in water. Water soluble arsenic species existing in natural water are inorganic arsenic (iAs) and organic arsenic (oAs) species. All acidic species, according to the chemical equilibrium, have well-recognized molecular and ionic forms in water. The distribution of iAs and oAs species is a function of pH value of water traces of arsenic that are found in groundwater, lakes, rivers and ocean. The WHO provisional guideline value for arsenic in drinking water is 10 μg L−1. The most selective and sensitive methods for determination of total arsenic and its species in water are coupled techniques including chromatography, optical methods and mass spectrometry. Determination of arsenic species is of crucial importance for selection of arsenic removal technology. Best available technologies are based on absorption, precipitation, membrane and hybrid membrane processes. Adsorption is considered to be relatively simple, efficient and low-cost removal technique, especially convenient for application in rural areas. Sorbents for arsenic removal are biological materials, mineral oxides, activated carbons and polymer resins.

• determination
• purification

Author Information

Ljubinka rajakovic *.

• Faculty of Technology and Metallurgy, University of Belgrade, Serbia

Vladana Rajakovic-Ognjanovic

• Faculty of Civil Engineering, University of Belgrade, Serbia

*Address all correspondence to: [email protected]

1. Introduction

Arsenic, As, belongs to the group of elements that are called metalloids. A metalloid is a chemical element that has properties of both metals and nonmetals. Arsenic is from all its features mostly recognized as a poison. Arsenic has a complex chemical behavior since it exists in four different oxidative states [ 1 ]. Depending on oxidative state and presence in environment, arsenic species exhibit different toxicity [ 2 ]. Arsenic species can be present in all types of environment and can originate from natural and anthropogenic sources [ 3 ]. Natural sources of arsenic are: rocks with incorporated arsenic compounds, activity of volcanoes and some biological processes. Anthropogenic sources are numerous, from mining to different types of production (pesticides, wood preservatives, and pigments). When the arsenic compounds reach groundwater, it is hard to distinguish the origin, both natural and anthropogenic arsenic species are released [ 3 ].

According to Science Direct, during the last decade, a significant number of scientific papers reporting the results from arsenic investigations are presented in Figure 1 . The focus of these researches was the development and improvement of methods for arsenic detection, extraction, separation and removal.

The number of publications with keyword arsenic, according to Science Direct.

The investigation of arsenic species and their behavior in various samples, especially in natural waters and environment is important for chemistry and environmental protection. The most common arsenic species are presented in Table 1

Common inorganic and organic arsenic species [ 5 ].

Depending on the oxido-reduction conditions, microbiological environment, arsenic species can be present in water in solution or in a precipitated form, and they can also adsorb or desorb from the existing precipitates [ 1 , 2 ]. When arsenic species are soluble in water, they can be present in both inorganic and organic forms. For iAs species both As(III), arsenite, and As(V), arsenate, can be present. For oAs species, MMA and DMA are soluble forms of organic arsenic species. From the value of the chemical equilibrium constants for each molecular or ionic form of arsenic in water, the present species can be recognized [ 3 ]. When choosing and analyzing the most dominant form of arsenic in water, the most present is inorganic arsenic as As(V). If As(III) is present, there are two important things that need to be taken into account. As(III) is more poisonous (even at low concentrations) than As(V). Beside the severe toxic effect, As(III) is easily oxidized. In oxidized conditions, stable forms of arsenic are As(V), and MMA and DMA, from oAs species. Many water sources in the world containing high concentration of arsenic cause health problems or diseases such as cancer. The WHO provisional guideline value for arsenic in drinking water is 10 μg L −1 [ 4 ]. Water quality analysis usually do not include test on arsenic. Arsenic compounds are colorless and odorless.

Once the presence of arsenic is determined in water, the separation and removal is obligatory. Removal technologies that are efficient, but still need improvement include absorption, precipitation, different electrochemical processes, membrane and hybrid membrane processes [ 6 , 7 , 8 , 9 ].

2. Arsenic in water

Arsenic enters the water through the dissolution of minerals, ores soil, sediments, water, living organisms and rocks containing high concentrations of arsenic. Drinking water from surface water bodies usually does not contain high concentrations of arsenic. Higher concentrations have only been found in the groundwater. Human activities influence and change the content of arsenic in nature. When using arsenic compounds for different purposes, there is a direct influence. There is also indirect influence that affects the mobility of arsenic from different natural sources. Organic arsenic compounds such as AsB, AsC, TETRA, TMAO, arsenosugars and arsenic-containing lipids are mainly found in marine organisms although some of these compounds have also been found in terrestrial species.

Despite the fact that iAs species are predominant in natural waters, the presence of oAs has also been reported. Even though the main analytical interest is to determine total arsenic in water, it is also important to develop the procedures for As species determination, separation, and removal. The distribution of i As and oAs species is a function of pH value of water [ 2 ].

The distribution of arsenic species vs. pH values of water is presented in Figure 2 [ 2 ].

The distribution of iAs and oAs species as a function of pH values of water [ 2 ]. Copyright approved by publisher.

As(III) species: H 3 AsO 3 , H 2 AsO 3 − , HAsO 3 2− and AsO 3 3− , are stable under slightly reducing aqueous conditions. As(V) species: H 3 AsO 4 , H 2 AsO 4 − , HAsO 4 2− and AsO 4 3− , are stable in oxygenated waters [ 6 ]. Two valences of the same element, molecular (ortho, H 3 AsO 3 , H 3 AsO 4 and meta forms, HAsO 2 , HAsO 3 ) and ionic forms with different charges make the research of arsenic removal from water more challenging and indivisible of arsenic chemistry knowledge. Any arsenic removal technology strongly depends on the water conditions and the stability of arsenic forms in the water.

Bearing in mind the fact that arsenic occurs in water in molecular and ionic form depending on water pH, the main goal of many investigations is to select the most efficient exchanger, not only in terms of efficiency, but also in terms of applicability in the wide range of water pH values in real and environmentally friendly water treatment systems. In neutral conditions, As(V) species are completely in ionic form (H 2 AsO 4 − and HAsO 4 2− ), while As(III) is in molecular (H 3 AsO 3 or HAsO 2 ), as shown in Figure 2 [ 2 ].

3. Determination of arsenic and arsenic species in water

There are a variety of chemical methods from classical to contemporary analytical techniques that are used for determination of arsenic and arsenic species in water.

There has been several review articles on the speciation of arsenic in a variety of samples [ 10 , 11 , 12 , 13 , 14 ]. These reviews focus on (1) determination of total content of arsenic and (2) speciation analysis.

A review of contemporary methods for arsenic and arsenic species in water is presented in Table 2 . The parameters, as detection limit, advantages and disadvantages are pointed out in order to have an insight into ability and application of available techniques.

A review of contemporary methods for arsenic and arsenic species determination in water.

The total concentration of arsenic in drinking water (mostly traces of arsenic, level of μg L −1 or less) can be detected only by sophisticated analytical techniques as ICP-MS, GF-AAS and HG-AAS [ 3 , 14 ]. For As speciation analysis, well-established methods that involve the coupling of separation techniques, such as HPLC with a sensitive detection system, that is, ICP-MS, are recommended, and they are mostly used [ 13 ].

Historically, colorimetric/spectrophotometric methods have been used to determine total arsenic concentration. Several commercial field kits have been based on Marsh and Gutzeit reaction. All As species in a sample reduce to As (arsenic mirror) or arsine, AsH 3 , (it passes on to an HgBr 2 -impregnated filter, turning it to yellow to brown color, depending on the amount of arsenic present). These tests are obvious, visible proofs for arsenic detection, and they are popular and useful in the field of forensic toxicology. The colorimetric methods are easy to use and inexpensive in terms of equipment and operator cost. They are useful for the semi-quantitative determination of high concentrations of arsenic in water. Spectrophotometric methods are based on conversion of arsenic to the colored compound such as molybdenum blue, or silver diethyldithiocarbamate [ 15 , 16 ].

Electrochemical methods , particularly voltammetric methods, are affordable, sensitive and ease of fabrication, and they are noteworthy for arsenic determination. Much work has been done in this area [ 12 ]. The ASV methods using platinum and gold electrodes, and CSV method using a glassy-carbon electrode have very low detection limit for arsenic determination. Determination of total As is performed by reducing As(V) to As(III) using various chemicals, and the limits of detection achieved were in vicinity of 0.02 μg L −1 . Also, arsenic in drinking water can be measured with Cu(II) by differential pulse cathodic stripping voltammetry (DPCSV) using hanging mercury drop electrode (HMDE) as working electrode and Ag/AgCl as reference electrode [ 12 , 17 , 18 ].

At present , for total As concentration determination, laboratories often prefer more sensitive methods such as AAS, AES, MS or AFS. Usually, the total concentration of arsenic needs to be determined, then the speciation analysis follows.

To perform speciation analysis properly, the best option is coupling of two analytical techniques. One technique is used for the separation of all chemical forms of arsenic that are present in water, and the other is used for the detection of these species. Besides coupling analytical techniques, there are necessary steps for complete analysis of arsenic. The first one is the extraction of arsenic, which has to be both mild and effective, at the same time. The second step is separation of various forms of arsenic species. The final step is the measuring step which gives the answer to the quantification of each present arsenic compound.

3.1. Sophisticated coupling technique

Analytical methods for determining different arsenic species have become increasingly important due to different toxicity and chemical behavior of various arsenic forms. Methods that involve the coupling of separation techniques, such as IC and HPLC with a sensitive detection system, such as ICP-MS, HG-AFS, HG-AAS and GF-AAS [ 3 , 11 , 13 , 14 , 19 ]. HPLC has been a preferred technique used for separation of arsenic compounds. Coupled with ICP-MS for determination, as HPLC-ICP-MS system it is a method of choice for separation and measurements all arsenic species in water. In addition, applying IC coupled with ICP-MS, it is possible to separate and estimate arsenic species in water: iAs(III), iAs(V), DMA, MMA, AsBet. A representative result is presented in Figure 3 [ 19 ].

Determination of five arsenic species by IC-ICP-MS. Mobile phase: NaOH [ 19 ].

The evaluation of analytical method is based on defining: selectivity, repeatability, accuracy, specific features of the method and defining the limits of detection and quantification (LoD and LoQ). These limits, these numbers give the information on the smallest concentration that can be detected and quantified with certain accuracy that has been defined [ 10 ]. The LoD was discussed and determined for the induced coupled plasma-mass spectrometry (ICP-MS) measurements of arsenic [ 11 ]. Thorough analysis has shown that the best option for LoD would be experiments, which would include the repetition many times. If experiments would be repeated 100 times, it is expected that only five measurements would be inadequate. Although this is ideal, the time consumption for the repetitive measurements is not acceptable. The most important conclusions were that LoD is not permanent and constant value, and it has to be verified and adopted for each new case. LoD is a basic parameter for estimation of the LoQ. It was concluded in [ 11 ] that the traditional (IUPAC) method is the one that could be applied.

4. Removal of arsenic and arsenic species from water

Different methods can be applied for arsenic removal from water. Arsenic (V) is more effectively removed than As(III) by both conventional and nonconventional methods. Pretreatmen (preoxidation) of As(III) to As(V) is an essential step for better removal [ 2 ]. Methods that have been successfully applied in water treatment plants are: precipitation and coprecipitation, electrochemical (such as electrocoagulation), ion exchange and MST (reverse osmosis, ultrafiltration and other membrane techniques) [ 6 , 7 , 8 , 9 , 20 , 21 ].

4.1. Sorption processes for arsenic separation and removal

A wide range of sorbent materials for aqueous arsenic removal has been tested and used: biological materials, mineral oxides, activated carbons and polymer resins. Even some agricultural and industrial by-products such as red mud, fly ash, waste iron slag from steel production plant and waste filter sand from water treatment plant, have proved to be good and inexpensive arsenic sorbents [ 6 , 7 ]. The potential use and application of industrial wastes in water treatment is in favor of the eco-friendly concept that preserves natural resources and supports the reuse-recycle concept. The technology of arsenic adsorption is based on materials which have a high affinity for dissolved arsenic. Adsorption of arsenic by iron modified sorbents has been established by several authors [ 6 , 7 ]. There are numerous scientific and professional investigations with intention to develop a small and efficient system for arsenic removal based on natural and artificial sorption materials [ 20 , 21 ]. Large amount of chemicals used for precipitation and coprecipitation processes (alum sulfate or ferric chloride) produce sludge, which needs treatment before disposal. If not treated properly, leachate with high concentration of arsenic is emitted to soil, threatening to contaminate the aquifers.

A step forward has been made by investigations that were devoted to the evaluation of selective multifunctional sorbents including ion-exchange resins for SPE and chromatographic columns connected with a sensitive measurements system [ 2 ]. The need to determine As species in water resulted in developing new materials for arsenic separation and removal. A simple procedure for selective separation (in pretreatment) of arsenic species in water using chemically modified and unmodified ion-exchange resins is presented in Figure 4 [ 2 ].

Procedure for selective separation arsenic species in water using ion-exchange resins [ 2 ]. Copyright approved by publisher.

For separation of As species in water, two types of resins, strong base anion exchange resin (SBAE), hybrid resins (HY) and hybrid resin chemically modified (HY-Fe and HY-AgCl), were tested and used. The HY-Fe resin retained all arsenic species except DMAs(V). This is recognized as an advantage because this makes direct measurement of this species in the effluent possible. The HY-AgCl resin retained all iAs, which was convenient for direct determination of oAs species in the effluent. The selective bonding of arsenic species on three types of resins, as shown in Figure 4 , has been established as the procedure which enables the separation and calculation of all arsenic species in water [ 2 ].

EC comprises complex chemical and physical processes involving many surface and interfacial phenomena. Very effective and perspective EC process consists of three processes: electrochemical reactions (simultaneous anodic oxidation and cathodic reduction), flotation and coagulation [ 9 , 20 ]. The EC process relies on the generation of metal ions from electrodes. The electrodes can be made of iron, aluminum or zinc, depending on the most favorable reactions for arsenic removal. The reaction in reaction chamber starts after the application of direct current. The electrode (metallic anode) dissociates into valent metallic ions. The metallic ions migrate to oppositely charged ions and the precipitation of different insoluble salts occur (different sulfides, oxides, hydroxides, chromates or phosphates, depending on the presence of ions in water). EC has several advantages when compared to other methods. The construction of reaction chamber is compact, control of the process is simple, no additional chemicals are required, and the result is reduced amount of sludge. If the electrode is made of iron, ferric hydroxide is one of the main solid products, as shown in Eq. (1) [ 9 ]:

Arsenate co-precipitates or adsorbs to Fe(OH) 3 (s), as shown in Eq. (2) .

The potential of EC as an alternative water treatment technique to remove arsenic from water needs to be realized [ 8 , 9 , 20 ].

Ion-exchange, IE, processes with regeneration capability is a proven, efficient and low-cost treatment method for the exchange of arsenic in the As(V) form [ 1 , 2 ]. The ion-exchange reaction between As(V) and a bed of chloride-form SBAE resin (designated as R-Cl resin) occurs as presented by Eq. (3) :

When the regeneration of resins is needed, both HCl and NaCl can be applied. Still, with HCl solution, more efficient regeneration occurs because the ionic forms of arsenic (anions) transform to molecular form (H 3 AsO 4 ). Molecular forms do not affect the equilibrium of ion-exchange processes as illustrated by Eq. (4) :

Different sorption processes, from adsorption, to chemisorption and ion-exchange, have shown a potential being efficient and cheap (depending on the selected sorbent). With improved, more selective and chemically modified sorbents, the extraction technique can be replaced [ 17 , 18 , 19 ]. What has been specifically used as an advantage for arsenic species separation is different behavior of arsenic species at various pH values [ 3 , 22 ].

The hybrid resin (HY) that has successfully been applied uses the activity of the hydrated iron oxides (HFO) and anion exchange for selective separation of arsenic [ 2 ]. With integrated use of anion exchange and sorption, the separation of As(III) and As(V) species and removal of all species of arsenic can be accomplished. With application of HY resin, two separate things can be accomplished: the collection and preconcentration of low concentrated iAs or the removal of iAs species, if it is interfering the determination.

Membrane separation technologies, such as RO, NF, UF, MF, can be employed in the removal of arsenic from water. Depending on the removal efficiency, RO and NF are more efficient than UF and MF. Operating conditions, membrane material, water quality, temperature, pressure, pH value and chemical compatibility have to be considered during operation of a membrane plant. When MF and UF are applied, less amounts of chemicals are used, and therefore, less sludge is produced. When RO and NF are used, no chemicals are needed and the amount of sludge is neglectable [ 8 ].

The comparison and future perspective of different technologies for arsenic removal are presented in Table 3 .

The comparison and future perspective of different technologies for arsenic removal.

5. Conclusion

Arsenic contamination of water has been reported as a critical issue in many articles, which reflects the latest state-of-the-art understanding of the behavior and toxicity of various arsenic species. Many water sources in the world contain low concentration of arsenic (mostly traces of arsenic, level of μg L −1 or less). If the concentration of arsenic in drinking water is higher than 10 μg L −1 , which is the WHO provisional guideline value for arsenic, it causes various health problems. All arsenic compounds dissolved in water are toxic. In natural waters, arsenic appears most often in inorganic forms and to a lesser extent in organic form. Inorganic species, arsenic acids (H 3 AsO 3 and H 3 AsO 4 ) and their ions are more toxic than organic forms. In addition, As(III) species are more toxic than As(V) ones. The valence (+III and +V), the type of arsenic species, ionic or molecular forms are dependent on the oxidation–reduction condition and pH of the water. Arsenic in water occurs in both inorganic and organic forms, but inorganic species are predominant in natural waters. In neutral conditions, As(V) species are completely in ionic form (H 2 AsO 4 − and HAsO 4 2− ), while As(III) is in molecular form (H 3 AsO 3 or HAsO 2 ).

Arsenic compounds are colorless and odorless, and testing water for arsenic is an important strategy for the health and well-being of people. Working with a water professional to monitor and maintain the quality of the well and water supply is an important responsibility.

In this work, methods for arsenic and arsenic speciation separation, determination and removal were reviewed. There are numerous methods for separation and determination of arsenic species in water. It is very important to recognize easy, simple and inexpensive methods to estimate the very low concentrations of arsenic.

The total concentration of arsenic in drinking water can be detected by simple Gutzeit method, and some similar colorimetric methods of comparing stains produced on treated paper strips. Although its minimum detectable concentration is 1.0·μ L −1 , these tests should be used when only a qualitative or semiqualitative detection is needed.

For precise, and reliable determination of arsenic in water, only sophisticated analytical techniques as ICP-MS, GF-AAS and HG-AAS can be applied. These methods are approved by US EPA. The features of these methods are high sensitivity, high accuracy, minimal sample volume; no sample pretreatment and short measurement time with minimum detectable concentration of 0.1 μ L −1 . They are expensive, need lot of knowledge for operating and interpretation of data.

For As speciation analysis, well-established methods that involve the coupling of separation techniques, such as HPLC with a sensitive detection system, that is, ICP-MS, are recommended, and they are mostly used. Through the limits, it is possible to define the smallest concentration of analyte that can be reliably detected and quantified. Limit of detection for the HPLC-ICP-MS system is 0.001 μ L −1 . This system is also expensive and needs lot of knowledge for operating and interpretation of data.

In all works, a special attention is paid to the preservation of arsenic species in environmental water samples for reliable speciation analysis. An appropriate procedure for the extraction of arsenic species from water should be accomplished without changing any original state of arsenic. This is still a challenging topic for research. The proposed system showed themselves to be accurate, precise and time efficient, as just a very simple sample treatment is required. Successful application of all methods required considerable practice.

Sorption processes (ion exchange, adsorption, chemisorption) with regeneration capability are proven as efficient and low-cost treatment methods for the removal of arsenic species from water. Separation of arsenic species using these new selective and chemically active sorbents recognize as a cost- and time-saving alternative to the traditional extraction techniques. The major drawback of all these techniques is that they are unable to remove As(III) efficiently.

Membrane separation technologies, such as RO, NF, UF, MF, are recommended for the removal of arsenic from water in water treatment plants.

Although there are numerous research papers focused on extraction techniques, yet it is not possible to set universal extraction procedures. These procedures depend on the presence of different species as well as on the type of matrices. For arsenic speciation, the choice of the most appropriate method is of great importance for obtaining reliable and accurate results.

Acknowledgments

The authors are grateful to the Ministry of Education and Science of the Republic of Serbia which supported our scientific work (projects no. TR37009, TR37010 and III43009).

Abbreviations

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Reportedly, 300 million people worldwide are affected by the consumption of arsenic contaminated groundwater. India prominently figures amongst them and the state of Bihar has shown an upsurge in cases affected by arsenic poisoning. Escalated arsenic content in blood, leaves 1 in every 100 human being highly vulnerable to being affected by the disease. Uncontrolled intake may lead to skin, kidney, liver, bladder, or lung related cancer but even indirect forms of cancer are showing up on a regular basis with abnormal arsenic levels as the probable cause. But despite the apparent relation, the etiology has not been understood clearly. Blood samples of 2000 confirmed cancer patients were collected from pathology department of our institute. For cross-sectional design, 200 blood samples of subjects free from cancer from arsenic free pockets of Patna urban agglomeration, were collected. Blood arsenic levels in carcinoma patients as compared to sarcomas, lymphomas and leukemia were found to be higher. The geospatial map correlates the blood arsenic with cancer types and the demographic area of Gangetic plains. Most of the cancer patients with high blood arsenic concentration were from the districts near the river Ganges. The raised blood arsenic concentration in the 2000 cancer patients strongly correlates the relationship of arsenic with cancer especially the carcinoma type which is more vulnerable. The average arsenic concentration in blood of the cancer patients in the Gangetic plains denotes the significant role of arsenic which is present in endemic proportions. Thus, the study significantly correlates and advocates a strong relation of the deleterious element with the disease. It also underlines the need to address the problem by deciphering the root cause of the elevated cancer incidences in the Gangetic basin of Bihar and its association with arsenic poisoning.

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An estimated 300 million people worldwide are affected with arsenic poisoning leading to health hazards 1 , 2 . The contamination of groundwater with arsenic occurs either through anthropogenic or geogenic sources. People residing in different countries are exposed to increased doses of arsenic via consumption of arsenic-rich groundwater 3 . Worldwide, major arsenic hotspots have been identified in Taiwan, Chile, Mexico, China, Bangladesh, India and Argentina. Other incidents involving smaller population groups have been reported in Poland, Hungary, Japan, Canada and USA 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 .

Bihar, a state in Eastern India, located in Ganga-Meghna-Brahmaputra (GMB) basin faces problems of arsenic contamination in groundwater. Groundwater is the main source of drinking water which caters more than 80 per cent of drinking source in rural Bihar, hence the size of population exposed to adverse effects of arsenic is very high. The other sources of drinking water such as dug well, pond, surface water like lakes and rivers have lesser or no incidence of arsenic contamination, but these sources are not commonly utilized for the drinking purpose. Before 1980s, the open well water as ground water source were considered safe for drinking water but in recent years, due to increased anthropogenic activities and geogenic reasons, the arsenic contamination in the Gangetic plains has increased many folds. Out of 38 districts of the state of Bihar, 18 districts have been reported high arsenic contamination in groundwater 12 . It is estimated that more than 10 million people in Bihar are drinking water with arsenic concentration greater than the WHO/BIS permissible limit of 10 μg/L 13 . According to Ministry of Water Resources, Government of India, 1600 habitations from 67 blocks of 18 districts of the states are severely affected with arsenic poisoning. This has caused threat to an estimated 50 million population of the state out of which 13.85 million people are drinking arsenic contaminated water above 10 μg/L 14 . Hence, the existence of arsenic menace among the population is presently more than the estimated survey. In Bihar, the problem of arsenic poisoning in ground water was reported for the first time in Simaria Ojhapatti village of Bhojpur district. The exposed population was so severely affected, that most of the village people evacuated their households. The subjects exhibited typical symptoms of arsenicosis along with other internal diseases as well 15 . In the recent reports, it has been found that the districts of Bihar like Buxar, Bhojpur, Patna, Saran, Vaishali, Samastipur, Begusarai, Khagaria, Munger, Bhagalpur etc. lying close to the banks of Ganga river are severely affected by arsenic 13 , 16 . The use of arsenic contaminated drinking water is the major cause for skin, lung, bladder, kidney cancer as well as other adverse health effects such as skin manifestations, gastrointestinal disorders, neurological effects, hormone disruption and infertility, posing a global health concern 17 , 18 , 19 , 20 . Basically, the arsenic enters the body through drinking and passes through the gastrointestinal tract and reaches the blood which reaches the vital organs of the body and causes organ toxicity which in turn disrupts the metabolic function of the body causing disease in them 21 , 22 , 23 , 24 , 25 .

According to Globocan 2018, 18.0 million new cancer cases, 9.5 million death and 43.8 million relapses (within 5 year of survival) was reported 26 . According to the national data of National Cancer Registry Programme of the Indian Council of Medical Research (ICMR), India has reported 3.9 million cancer cases in 2016. The worst cancer affected states were Uttar Pradesh with 674,386 cases, followed by Maharashtra with 364,997 and Bihar with 359,228 while in south India, Tamil Nadu recorded 222,748 cases, Karnataka 202,156, Andhra Pradesh 159,696, Telangana 115,333 and Kerala 115,511 cases of cancer 27 .

The increased incidences of cancer in the state of Bihar has been a major challenge for the Government. The etiology of cancer incidences in this area has not been revealed properly. Hence, the present study is an approach to decipher the root cause of the cancer incidences in the Gangetic basin of Bihar and its association with arsenic.

Materials and methods

The study was conducted at Mahavir Cancer Sansthan and Research Centre, Patna, Bihar. Altogether, 2000 cancer patients were identified and their blood samples were collected for the study. For the cross-sectional design, 200 blood samples of subjects free of cancer from arsenic free pockets of Patna urban agglomeration, Bihar were also collected as control.

Selection of subjects for the study

Cancer patients: In our cancer institute, approximately 15,000 confirm cancer cases are reported annually. For the present study, 2000 cancer confirm patients were randomly selected from the year 2017 to 2019. The selection of the patients was carried out randomly in the OPD of the institutes. For the diagnosis of the disease, various tests were carried out and after the confirmation of malignancy, they were recommended for the present study and their blood samples were collected.

Control subjects: For the cross-sectional study, 200 subjects of urban Patna district of Bihar were selected as the control subjects. These subjects were from non- arsenic hit area of the district. These control subjects were taken in the study to compare the blood arsenic concentration between a normal subject versus cancer patients.

Blood collection from the control subjects and cancer patients:

In the collection procedure, 5 ml of blood by volume was taken from the peripheral vein of the arm using disposable syringes and transferred to heparinised vaccutainer as per the guidelines of IUPAC 28 .

After the collection, all the blood samples were double digested using concentrated HNO 3 on hot plate under fume hood and estimated as per the protocol of (NIOSH) 29 through Graphite Furnace Atomic Absorption Spectrophotometer (Pinnacle 900T, Perkin Elmer, Singapore).

The patient based epidemiological data like patient’s age, gender, demographic area, cancer disease type, cancer stage etc. were collected from the patient files in the record room of MCSRC.

GIS analysis and geo spatial mapping

The data of arsenic concentration in blood samples of the subjects were taken as input in Arc-GIS 10 software for spatial analysis, correlation, exposure rate and to visualize a synoptic view of the district-wise exposure rate. Concentrations of arsenic in blood data of the cancer patients were analysed with generation of statistical data in form of map and categorization therein. The arsenic background status map of Bihar was used for visualizing the exposure rate. All the layers were analysed using ArcGIS environment. The final output was generated as a thematic map. The software used in the map layer generation is ArcMap10.5.1, ESRI, ArcGIS Desktop 10.5.1 licensed at TU Delft Faculty of Civil Engineering and Geosciences. All the shapefiles were created in the ArcGIS environment for which base map was extracted from OpenStreetMap data downloaded from the link " http://download.geofabrik.de/asia/india.html ". (OpenStreetMap contributors. (2017). Planet dump retrieved from https://planet.osm.org , https://www.openstreetmap.org ).

The data was reported to the Mahavir Cancer Sansthan and Research Centre which brought to light significant findings in regards to the study.

Statistical analysis

Data were analyzed with statistical software (Graph Pad Prism 5) and values were expressed as mean ± SEM. Differences between the groups were statistically analyzed by one-way analysis of variance (ANOVA) using the Dunnett’s test. The scattered graphs were plotted through another statistical software SPSS-16.0 using linear regression analysis model as earlier used 30 .

Ethical approval

Ethical approval was obtained from the Institutional Ethics Committee (IEC) of Mahavir Cancer Sansthan and Research Centre with IEC No. MCS/Research/2015-16/2716, dated 08/01/2016.

The present study shows significant epidemiological information of 2000 cancer patients and 200 control subjects. The factors of age, gender, cancer type, blood arsenic concentration in blood of cancer patients and control subjects were given cognizance. Correlation coefficients of arsenic in blood and cancer subjects age, geospatial distribution of cancer patients and cancer type details were accounted.

Gender wise—Cancer patients vs control subjects: Total 2000 blood samples of patients were analysed, out of which n = 1213 patients were cancer female patients while n = 787 subjects were male cancer patients. In the total studied 200 control subjects, n = 112 were the female subjects, while n = 88 were the male subjects (Fig.  1 ).

Age wise in female cancer patients: In total n = 1213 female cancer patients, the maximum cancer incidences were observed in the patient’s age group between 31–70 years. In the control female subjects n = 112, the maximum studied groups were between 21–70 years of age group. The age group between 21–30 had the highest number of the studied subjects n = 56 (Fig.  2 ).

Age wise in male cancer patients: In total n = 787 male cancer patients, the maximum cancer incidences were observed in the patient’s age group between 21–70 years. In the control male subjects n = 88, the maximum studied groups were between 21–70 years of age group. The age group between 21–30 had the highest number of the studied subjects n = 44 (Fig.  3 ).

Type of cancer in female and male cancer patients: Out of n = 1213 females, n = 1088 cases were of solid tumours while, n = 125 females were of haematolymph cases while, out of n = 787 males, n = 644 cases were of solid tumours while, n = 143 males represented haematolymph cases (Fig.  4 ).

Blood arsenic concentration in female cancer patient’s vs female control subjects: Out of total n = 2000 blood samples of cancer patients analysed, n = 1213 (60%) blood samples were of female patients and the maximum arsenic concentration in their blood sample reported was 2048 μg/L. The minimum value of arsenic in blood was observed to be between 0-10 μg/L. In the present data, n = 523 (43.11%) blood samples were in the minimum range between 0–10 μg/L, out of which n = 395 patients had their blood arsenic concentration values less than 1.0 μg/L. The n = 102 subjects had the blood arsenic concentration between the range 11–20 μg/L. The rest n = 588 (48.47%) patients had the blood arsenic concentration more than the minimum range. In the control female subjects n = 112, maximum subject n = 98 (87.5%) had the blood arsenic concentration with in the minimum range 0–10 μg/L, the rest n = 14 (12.5%) had mild blood arsenic concentration in their bloods in the range between 11–20 μg/L. The maximum arsenic concentration in their blood sample reported was 19.4 μg/L (Fig.  5 ).

Blood arsenic concentration in male cancer patient’s vs male control subjects: Out of total n = 2000 blood samples of cancer patients analysed, n = 787 (40%) blood samples were of male patients and the maximum arsenic concentration in their blood sample reported was 2432 μg/L. The minimum value of arsenic in blood was observed to be between 0–10 μg/L. In the present data, n = 323 (41.04%) blood samples were in the minimum range between 0–10 μg/L, out of which n = 236 patients had their blood arsenic concentration values less than 1.0 μg/L. The n = 77 subjects had the blood arsenic concentration in the range 11–20 μg/L. The rest n = 387 (49.17%) patients had the blood arsenic concentration more than the minimum range. In the control male subjects n = 88, maximum subject n = 79 (89.7%) had the blood arsenic concentration with in the minimum range 0–10 μg/L, the rest n = 9 (10.2%) had mild blood arsenic concentration in their bloods in the range between 11–20 μg/L. The maximum arsenic concentration in their blood sample reported was 19.6 μg/L (Fig.  6 ).

Correlation coefficient between blood arsenic levels and age of the female and male cancer patients: The study showed significant increase in blood arsenic levels in the female cancer patients (r = 0.005 and P < 0.05) and male cancer patients (r = 0.003 and P < 0.05) (Fig.  7 ).

Correlation coefficient between blood arsenic levels and age of the female breast cancer patients: The study showed significant increase in the blood arsenic levels in the female breast cancer patients n = 401; (P < 0.05) (Fig.  8 ).

Correlation coefficient between blood arsenic levels and age of the female ovarian and cervical cancer patients: The study showed significant increase in the blood arsenic levels in the female ovarian (n = 39) and cervical (n = 203) cancer patients (P < 0.05) (Fig.  9 ).

Correlation coefficient between blood arsenic levels and age of the Gall bladder Cancer—female vs male patients: The study showed significant increase in the blood arsenic levels in the female (n = 93) vs male (n = 82) gallbladder cancer patients; (P < 0.05) (Fig.  10 ).

Correlation coefficient between blood arsenic levels and age of the Gastrointestinal Cancer—female vs male patients: The study showed significant increase in the blood arsenic levels in the female (n = 96) vs male (n = 88) gastrointestinal cancer patients (P < 0.05). This includes total gastrointestinal cancer cases (n = 184). Out of which the cancer of stomach was (n = 90), esophagus (n = 18), iliac (n = 09), colon (n = 21), rectum (n = 29) and anus (n = 17) (Fig.  11 ).

Correlation coefficient between blood arsenic levels and age of the Liver Cancer—female vs male patients: The study showed significant increase in the blood arsenic levels in the female (n = 64) vs male (n = 54) liver cancer patients; (P < 0.05) (Fig.  12 ).

Correlation coefficient between blood arsenic levels and age of the Lung Cancer—female vs male patients: The study showed significant increase in the blood arsenic levels in the female (n = 27) vs male (n = 37) lung cancer patients; (P < 0.05) (Fig.  13 ).

Correlation coefficient between blood arsenic levels and age of the Head and Neck Cancer—female vs male patients: The study showed significant increase in the blood arsenic levels in the female (n = 75) vs male (n = 268) head and neck cancer patients; (P < 0.05) (Fig.  14 ).

Correlation coefficient between blood arsenic levels and age of the Urinary bladder and Kidney Cancer—female vs male patients: The study showed significant increase in the blood arsenic levels in the female (n = 10) vs male (n = 18) urinary bladder and kidney cancer patients; (P < 0.05) (Fig.  15 ).

Correlation coefficient between blood arsenic levels and age of the female and male genital cancer patients: The study showed significant increase in the blood arsenic levels in the female (n = 73) genital cancer patients (P < 0.05). The female genital cancer cases included cancer of vagina, vault and uterus. The study also showed significant increase in the blood arsenic levels in the male (n = 42) genital cancer patients (P < 0.05). The genital cancer cases included cancer of prostate, testis, penis, seminal vesicle and scrotum (Fig.  16 ).

Geospatial Cancer distribution Map of 2000 Cancer patients with Average Blood Arsenic concentration—district wise: The district wise map shows the geospatial distribution of 2000 cancer patients with average blood arsenic concentration (Fig. 17 ).

Cancer types: The cancer types have been primarily categorised into 04 major parts—leukaemia’s, lymphomas, sarcomas and carcinomas. They have been further categorised into 18 subtypes. All the data have been correlated with blood arsenic concentration and their age. In carcinomas, the maximum number observed were of Breast cancer (n = 401), Head and Neck cancer (n = 343), Cervical cancer (n = 203), Gastro intestinal cancer (n = 184), Gall bladder cancer (n = 175), Liver cancer (n = 118) and the remaining types had their numbers less than 100. (Table 1 ).

Geospatial distribution of Cancer types: The maps show the district wise geospatial distribution of cancer types with average blood arsenic concentration. The district wise distribution with average blood arsenic is very significant with the level of arsenic exposure in Carcinoma (Fig.  18 A), Lymphoma (Fig.  18 B), Leukemia (Fig.  18 C), Sarcoma Fig.  18 D).

Skin cancer patient with arsenicosis symptoms : The studied patient was having skin cancer—squamous cell of carcinoma, drinking arsenic contaminated water of 322 μg/L and his blood arsenic concentration was 86.4 μg/L (Fig.  19 ).

Graph showing number of patients (gender wise) in cancer patients and control subjects (ANOVA-Dunnett’s Test, P < 0.05).

Graph showing age wise distribution of female cancer patients and control female subjects. (ANOVA-Dunnett’s Test, P < 0.05).

Graph showing age wise distribution of male cancer patients (ANOVA-Dunnett’s Test, P < 0.05).

Graph showing type of cancer in female and male patients (ANOVA-Dunnett’s Test, P < 0.05).

Arsenic concentration in blood samples of female patients were analyzed through GF-AAS (ANOVA-Dunnett’s Test, P < 0.05).

Arsenic concentration in blood samples of male patients were analyzed through GF-AAS (ANOVA-Dunnett’s Test, P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female (n = 1213) (r = 0.005 and P < 0.05) and male (n = 787) cancer patients (in years) (r = 0.003 and P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female breast cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female ovarian and cervical cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male gallbladder cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male gastrointestinal cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male liver cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male lung cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male head and neck cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male urinary bladder and kidney cancer patients (P < 0.05).

The correlation coefficient between blood arsenic levels and age of the female vs male genital cancer patients (P < 0.05).

Geospatial Cancer distribution Map of 2000 Cancer patients with Average Blood Arsenic concentration—district wise [Base map extracted from OpenStreetMap—( http://download.geofabrik.de/asia/india.html ) using ArcMap10.5.1].

( A ) Geospatial distribution of Carcinoma Cancer patients with Average Blood Arsenic Concentration [Base map extracted from OpenStreetMap—( http://download.geofabrik.de/asia/india.html ) using ArcMap10.5.1]. ( B ) Geospatial distribution of Lymphoma Cancer patients with Average Blood Arsenic Concentration [Base map extracted from OpenStreetMap—( http://download.geofabrik.de/asia/india.html ) using ArcMap10.5.1]. ( C ) Geospatial distribution of Leukemia Cancer patients with Average Blood Arsenic Concentration. [Base map extracted from OpenStreetMap—( http://download.geofabrik.de/asia/india.html ) using ArcMap10.5.1]. ( D ) Geospatial distribution of Sarcoma Cancer patients with Average Blood Arsenic Concentration. [Base map extracted from OpenStreetMap—( http://download.geofabrik.de/asia/india.html ) using ArcMap10.5.1].

Showing a cancer patient with skin cancer (squamous cell of carcinoma) in his palm with typical arsenicosis symptoms in sole and palm.

Geological perspective

A detail assessment of incidence of arsenic in groundwater has been attempted in the middle Ganga plain in the Bhojpur and Patna districts of Bihar to study the distribution pattern and controlling factors of its occurrence. Groundwater samples were tested with field kit for arsenic, 3D surface maps were prepared at different depth levels and a positive correlation of geomorphology and depth with incidence of arsenic was worked out. It was observed that while the older alluvium surface in the area is free from hazardous incidence of arsenic, the older/present day flood plain surface has several localized pockets of higher incidence of arsenic (50 to  > 500 μg/L). There is a specific depth control observed where the aquifer within 12–75 m depth range is yielding arsenic. Since, older alluvium (Peninsular origin) is free from hazardous incidences of arsenic in ground water, the source of arsenic contamination in the ground water appears to be associated with the holocene sediments of the Himalayan provenance brought down by the river Ganga and its tributaries of extra peninsular (Himalayan) origin 31 .

Ethics approval and consent to participate

Ethical approval was obtained from the Institutional Ethics Committee (IEC) of Mahavir Cancer Sansthan and Research Centre with IEC No. MCS/Research/2015-16/2716, dated 08/01/2016. Furthermore, it is also certified that the informed consent was taken from the individuals who voluntarily participated in this study while the minor’s parents provided us the informed consent for this particular study.

In the human metabolic system, inorganic arsenic through drinking water reaches the blood through gastrointestinal tract. It is easily converted into organic form which in excess is primarily eliminated through urine. In the blood it remains for 2–6 hours and is mostly eliminated through the renal system 32 , 33 . It is also deposited in the keratin of skin, hair and nails and alters the epidermal keratinocytes causing keratosis, melanosis, rain drop pigmentation or other skin manifestations 34 . The arsenic adversely effects the epidermal system, the vascular system and the nervous system of human beings. The acute poisoning causes vomiting, diarrhea, abdominal pain, general body weakness, vertigo, nausea, muscle cramps etc. The long duration arsenic exposure causes skin manifestations like keratosis, melanosis in sole and palm along with rain drop pigmentation all over the body. Further, it also causes peripheral neuropathy, renal failure, gastrointestinal disruption, hypertension, diabetes, conjunctivitis, anaemia, loss of appetite, breathlessness, mental disability, hormonal imbalances, suppression of bone marrow and cardiovascular diseases 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 . The trivalent arsenic is more toxic than the pentavalent arsenic hence is known to be a carcinogen 4 , 10 , 45 , 46 . There are mainly three ways by which humans are exposed to arsenic—drinking arsenic contaminated groundwater, food prepared with the arsenic contaminated water and food crops irrigated with high arsenic contaminated groundwater. This causes entry of arsenic into human body through various routes causing life threatening disease like cancer of the skin, bladder, lungs, kidney, liver, and prostate 47 . There is adequate evidence which states that arsenic causes carcinogenicity in humans and the International Agency for Research on cancer has classified arsenic as Category-I carcinogen 4 . The skin cancer, Bowen’s disease and squamous cell carcinoma are very common in arsenic exposed population 4 , 48 , 49 , 50 , 51 . In recent studies, it has been found that arsenic is causing reproductive health hazards as cases of spontaneous abortion, stillbirth and preterm birth. The pregnant women who are continuously drinking arsenic contaminated water are also exposing their foetus through placenta causing severe health problem for the child after birth 52 , 53 .

During the course of this study, we have observed very high arsenic concentration in ground water samples (1929 μg/L) in Buxar district of Bihar. From the same household, we have also observed the blood arsenic concentration in a subject as 664.6 μg/L which is the highest reported case in the state of Bihar showing typical symptoms of arsenicosis 12 . Similar studies have been reported by many other researchers 54 , 55 , 56 , 57 , 58 , 59 , 60 .

The blood arsenic concentration in the exposed population has been rarely studied, since it is thought to be very weak biomarker. Hence, there had been no benchmark established for the blood arsenic concentration for humans. The present comprehensive study carried out is the world’s first study which deciphers the association between arsenic and cancer through blood arsenic study. In the present study, there was significantly high arsenic concentration in the blood samples of cancer patients especially in the females in comparison to male. This denotes that there is some pathway, which makes the arsenic exposed population more vulnerable, which subsequently due to sustained exposure gets converted into a life-threatening disease like cancer. Secondly, the significant levels of arsenic concentration have a distinct correlation with the incidences of cancer patients. The cross-sectional design also correlates that the non-cancer subjects (control subjects) hardly had any arsenic exposure, as n = 135 had zero arsenic concentration, while n = 42 between 1–10 μg/L of minimum range. However, n = 23 had very mild blood arsenic concentration levels between 10–20 μg/L. This explains our observations made as a part of study. Moreover, out of 2000 studied cancer cases, in the n = 1154 (57.7%) cancer cases, the blood arsenic concentration was found to be more than the minimum range (0–10 μg/L) and while n = 846 (42.3%) were in the minimum range. The coefficient correlation also is directly proportional to higher the age of the subject, more is the blood arsenic concentration. Thus, arsenic is first weakening the immune system and then causing the health ailments like cancer. The geospatial distribution of studied cancer patients with blood arsenic concentration in their blood also correlates that the disease burden is very high in the Gangetic basin of the state where the arsenic contamination in ground water is also relatively very high 61 , 62 , 63 . In a recent study carried out by our team in Patna district, Bihar, cancer mapping in Gyaspur Mahaji village has been extensively done to establish the relation and the study strongly correlates the association 64 .

Various studies have deciphered the molecular pathway of arsenic causing cancer in the subjects from arsenic exposed area. In squamous cell carcinoma of skin, arsenic binds with the receptors and disrupts the signal transduction pathways. The arsenic affinity to bind with sulfhydryl (SH) groups causes release of Reactive Oxygen Species (ROS) which leads to cellular toxicity and metabolic dysfunction 65 , 66 . The interaction of arsenic with thiol groups is associated with 200 known human proteins. These interactions cause production of ROS which leads to activation of oncogenes, upregulation of inflammatory pathways and inhibition of the function of tumour suppressor genes 41 , 67 , 68 , 69 , 70 , 71 .

In a recent study by some researchers, it is speculated that arsenic activates the cell proliferation through Canonical Hippo Signaling pathway which causes various types of malignancies including skin cancer 72 , 73 . Furthermore, arsenic upregulates the various components of Hippo signaling including mammalian STE20-like kinase STE20-like kinase 1/2 (Mst1), Salvador homolog 1 (Sav1), large tumour suppressor kinase 1/2 (LATS1) and Mps one binder kinase activator-like 1A (MOB1). In the epithelial cell proliferation Yes-associated protein (YAP) is a responsible component is dephosphorylated by arsenic causes the control over tight/adherens junctions of the epithelium 74 , 75 . In the recent times, various cancer types and its cause due to arsenic has been established say in case of bladder cancer 76 , 77 , 78 , 79 , 80 , 81 , 82 , for lung, kidney and laryngeal cancer 83 , 84 , 85 , 86 . In a study conducted in Brazil showed significant levels of blood arsenic in maternal chord blood with limit above 3.30 µg/L 87 . Study in another city in Brazil showed significant blood arsenic reference value as 9.87 µg/L 88 . While in a study carried out in 32 children in Yucatan, Mexico showed blood arsenic levels above 10 µg/L in 37% of the samples 89 . In a similar study conducted on 120 arsenic exposed residents (76 breast cancer cases) of Camarca Lagunera, Mexico showed the expression of Yes- Associated Protein (YAP), a tumour suppressor protein along with apoptosis inhibitor was measured. The result showed low percentage of YAP expression denotes abnormal expression of YAP in arsenic exposed breast cancer patients 90 , 91 .

Our institute (MCSRC) has registered more than 15,000 cancer cases in year 2019. The epidemiological data showed that most of the cancer cases reported were from the cities or towns which are located near the river Ganga. The most incidences of cancer cases were from the districts—Buxar, Bhojpur, Saran, Patna, Vaishali, Samastipur, Munger, Begusarai Bhagalpur etc. Various studies have reported that arsenic in the form of arsenopyrite load has reached these river basins in the form of silt from great Himalayas and has caused geogenic changes in the sediments and ground water causing health hazards to the exposed population 92 , 93 . It is evident from many studies that consumption of arsenic contaminated groundwater for drinking purposes and contaminated food has caused health related issues in the population in long duration exposure finally leading to cancer disease. Our epidemiological data also suggests that the districts located near the course of Himalayan bound river basins have more incidences in comparison to non-Himalayan river basins. Most common cancer cases recorded were of skin cancer, skin melanoma, lung cancer, bladder cancer, hepatobiliary cancer, renal cell carcinoma, breast cancer, ovarian cancer, endometrium cancer etc. with typical symptoms of arsenicosis denotes that there is a significant correlation with the arsenic. The arsenic contamination in the long duration of exposure is causing the exposed population contract the disease in primary phase and then acquiring second stage of disease, if not cured in time. It is quite possible that arsenic along with other confounding factors could be adding the disease burden. Apart from this, the cancer disease types like carcinomas are more aggressive than the other types like leukemias, lymphomas and sarcomas. The pathways related to cause of cancer in the arsenic exposed population needs further studies for the final validation and establishment of benchmark for blood arsenic concentration in humans.

The present study demonstrates the high incidence of cancer in arsenic prevalent, Gangetic basin. The study strongly correlates the association between arsenic and cancer incidence in the arsenic exposed population of Bihar in which significantly high arsenic concentration has been observed in the blood samples of cancer patients. Arsenic exposure also correlates with the high incidence of cancer disease burden in the carcinoma type of cancer in comparison to the sarcomas, lymphomas and leukemias type of cancer. This study reiterates the fact that the people living in the Gangetic basin are getting exposed to the continued arsenic toxicity leading to the development of several types of cancers. More systematic study is further required to understand the molecular mechanisms of arsenic toxicity in incidences of cancer and its progression and to establish the correlation by deciphering the signaling pathways for arsenic exposed human cancer. All this effort will eventually lead to the development of improved therapeutic approach.

Data availability

The data that support the findings of this study is available from the corresponding author upon reasonable request.

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Acknowledgements

The authors are thankful to the institute (MCSRC) for providing all necessary infrastructures required for this particular study. The financial assistance for the study was provided by the institute itself.

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A.K. and A.K.G. Conceptualized the entire work, A.K. had the major contributions in writing the manuscript but support was also provided by A.K.G., D.K., and A.B., literature search was done by V.A. and V.K., data were collected by M.K., G.A., R.K.P. and P.S., experimental work and data analysis were done by M.K., P.K.N. and P.S., data interpretation was carried out by A.K., M.A., R.K., D.K., A.B., and R.R., final figures were designed by A.K. and S.K.. All authors read and approved the final paper.

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Kumar, A., Ali, M., Kumar, R. et al. Arsenic exposure in Indo Gangetic plains of Bihar causing increased cancer risk. Sci Rep 11 , 2376 (2021). https://doi.org/10.1038/s41598-021-81579-9

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DOI : https://doi.org/10.1038/s41598-021-81579-9

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Arsenic, drinking water, and health: a position paper of the American Council on Science and Health

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• 1 Kbinc, Chapel hill, North Carolina 27516, USA.
• PMID: 12460751
• DOI: 10.1006/rtph.2002.1573

The purpose of this American Council on Science and Health report is to review issues and sources of uncertainty affecting assessment of potential health risks related to drinking water in the United States. Some background is included on how these issues arose, as is a review of the 1999 National Research Council report (with references to an updated version), to formulate a position based on the current science concerning how much of a risk of adverse health effects actually exists from arsenic in drinking water in the United States. ACSH concludes that there is clear evidence that chronic exposure to inorganic arsenic at concentrations of at least several hundred micrograms per liter may cause: (1) cancer of skin, bladder, lung (and possibly several other internal organs, including kidney, liver, and prostate), and (2) noncancer effects, including classic cutaneous manifestations that are distinctive and characteristic of chronic arsenic poisoning (diffuse or spotted hyperpigmentation and palmar-plantar hyperkeratoses). Noncancer effects may be multisystemic, with some evidence of peripheral vascular, cardiovascular, and cerebrovascular disease, diabetes, and adverse reproductive outcomes. Further study is needed to know if beneficial effects of arsenic in animal studies apply to humans. ACSH concludes that there is little, if any, evidence of a detrimental health effect in humans from inorganic arsenic in drinking water at the current maximum contaminant level (MCL) of 50 microg/L or below, either in the United States or elsewhere. As noted in the 1999 NRC report, "No human studies of sufficient statistical power or scope have examined whether consumption of arsenic in drinking water at the current MCL results in an increased incidence of cancer or noncancer effects" (NRC, 1999, p. 7). Based on our review, described in this article, ACSH finds that the limitations of the epidemiological data available and the state-of-the-science on the mode-of-action of arsenic toxicity, including can cer, are inadequate to support the conclusion that there are adverse health effects in the United States from arsenic in drinking water at or below the limit of 50 microg/L.

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In terms of its impact on human health, arsenic is unique in that most of the evidence linking it to diseases comes from epidemiological work; animal studies have not provided good models. It is also unique in causing a large number of different damaging effects and, as more studies are conducted, more such effects are found. To date, we know that arsenic from drinking water can cause severe skin diseases including skin cancer; lung, bladder, and kidney cancers, and perhaps other internal tumors; peripheral vascular disease; hypertension; and diabetes. It also seems to have a negative impact on reproductive processes (infant mortality and weight of newborn babies). The toxicology of arsenic involves mechanisms that are still not completely understood, but it is clear that a number of factors can affect both individual and population-level susceptibility to the toxic effects of arsenic-contaminated drinking water. Current research is addressing some of these, including genetic susceptibility and lifestyle factors that may increase arsenic's toxic effects, such as smoking, diet, and concurrent exposure to other substances. The reversibility of some effects upon cessation of exposure is also being investigated.

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Impact of Water Regimes on Minimizing the Accumulation of Arsenic in Rice ( Oryza sativa L.)

• Published: 07 September 2022
• Volume 233 , article number  383 , ( 2022 )

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• Muhammad Tahir Shehzad   ORCID: orcid.org/0000-0002-7365-3147 1 ,
• Muhammad Sabir 1 ,
• Saifullah 1 ,
• Abu Bakkar Siddique 2 , 3 ,
• Mohammad Mahmudur Rahman 2 , 3 &
• Ravi Naidu 2 , 3  

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Arsenic (As) is very common pollutant of the environment categorized as class-I human carcinogen. Rice crop is inherently efficient at accumulating As that is also triggered by conventional cropping methods (flooded conditions). A pot experiment was conducted with the objectives to (i) determine the accumulation of As in rice grains and shoots and As species in rice grains, (ii) determine the effect of As concentrations on physiological and agronomic characteristics of the rice crop, and (iii) assess the changes in fractions of As within the soil under different water regimes. Water regimes included flooding, intermittent, intermittent + aerobic, and aerobic irrigation. Grain As concentration from flood-irrigated rice was significantly ( P  ≤  0.05 ) reduced in rice grown in 10 and 50 mg kg −1 As-contaminated soil with less applied irrigation. Water management techniques have influenced As speciation in rice grains. As the irrigation techniques were shifted from flooding to intermittent, intermittent + aerobic, and aerobic irrigation, a significant decrease in concentration of inorganic species (11.98–76.81% at 10 mg kg −1 and 66.04–93.61% at 50 mg kg −1 ) was observed. Aerobic irrigation has effectively reduced the concentration of arsenic in rice grain as compared to other irrigation techniques in both the As-contaminated soils. This study indicated that irrigation management techniques other than flood irrigation have significantly affected the As (total and speciation) concentration within the rice grains and non-significantly affecting crop yield and this must be considered if regulations are based on inorganic As percentage of total As concentration.

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Agricultural Water Management Practices and Environmental Influences on Arsenic Dynamics in Rice Field

Arsenic uptake, accumulation and toxicity in rice plants: possible remedies for its detoxification: a review, effect of selenium application on arsenic uptake in rice (oryza sativa l.), data availability.

This is the original data presented in this manuscript.

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Acknowledgements

We, the authors, are very thankful to the Higher Education Commission (HEC), Islamabad, for providing funds to conduct this research in Pakistan under the HEC-5000 Indigenous Program and to perform analytical work at Global Centre for Environmental Remediation, University of Newcastle, Australia, under its International Research Support Initiative Program (IRSIP).

Higher Education Commision,Pakistan,417-55070-2AG4-001,Muhammad Tahir Shehzad,IRSIP 38 Agri 14,Muhammad Tahir Shehzad

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Dr. M. T. Shehzad, has collected, prepared, and analyzed the samples and performed statistical data analysis and written a manuscript. Dr. M. Sabir has supervised the whole research. Dr. Saifullah, Mr. A. B. Siddique, and Dr. M. M. Rahman have helped in writing and critically reviewing the manuscript. Samples were analyzed at Global Centre for Environmental Remediation, University of Newcastle, Australia, under the supervision of Prof. Ravi Naidu.

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• Arsenic (As), class-A human carcinogen, is ubiquitously present in the environment.

• Rice crops are inherently efficient at accumulating As triggered by continuous flooding.

• Aerobic irrigation effectively reduces the concentration of arsenic in rice grains.

• Arsenic levels were determined using an inductively coupled plasma–mass spectrometer.

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Shehzad, M.T., Sabir, M., Saifullah et al. Impact of Water Regimes on Minimizing the Accumulation of Arsenic in Rice ( Oryza sativa L.). Water Air Soil Pollut 233 , 383 (2022). https://doi.org/10.1007/s11270-022-05856-7

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DOI : https://doi.org/10.1007/s11270-022-05856-7

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Health risk assessment of arsenic and lead contamination in drinking water: A study of Islamabad and Rawalpindi, Pakistan

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Muhammad Tauseef Azam , Asif Ahmad , Anwaar Ahmed , Azeem Khalid , Samreen Saleem; Health risk assessment of arsenic and lead contamination in drinking water: A study of Islamabad and Rawalpindi, Pakistan. Water Supply 2024; ws2024135. doi: https://doi.org/10.2166/ws.2024.135

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The present research study explores the drinking water quality of Rawalpindi and Islamabad to identify the potent dissolved contaminants and carry out a health risk assessment as the study area houses more than 3 million people. Drinking water samples were collected from 95 union councils of the selected study area and were investigated for 12 physicochemical water quality indicators. The collected datasets were interpreted using general statistics, principal component analysis and spatial analysis for knowing the variations among the collected samples. The results revealed that overall 51.57% of the drinking water samples were unsatisfactory for human consumption. The rate of physicochemical contamination was 87.27% in the rural and unauthorized housing societies. Arsenic (As) and lead (Pb) were the potent contaminants in the drinking water samples. The health risk assessment uncovered that 31.57 and 10.45% of samples had a hazard quotient (HQ) >1 for arsenic and lead, respectively. Collectively, 41 drinking water sources were identified as potential health risk sources for the residents.

Planned sampling from 95 locations was carried out from in-use drinking water sources from the capital city Islamabad and Rawalpindi, Pakistan.

Assessment of health risks for arsenic and lead was carried out using the standard guidelines of USEPA.

The combination of spatial analysis with water quality indicators provides disseminated research findings to the general public along with scientific researchers.

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Arsenic contamination of food and water is a global public health concern – researchers are studying how it causes cancer

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Diana Azzam receives funding from the Florida Department of Health and the National Institute of Health.

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Arsenic is a naturally occurring element found in the Earth’s crust. Exposure to arsenic, often through contaminated food and water, is associated with various negative health effects, including cancer .

Arsenic exposure is a global public health issue. A 2020 study estimated that up to 200 million people wordwide are exposed to arsenic-contaminated drinking water at levels above the legal limit of 10 parts per billion set by the U.S. Environmental Protection Agency and World Health Organization. More than 70 countries are affected, including the United States, Spain, Mexico, Japan, India, China, Canada, Chile, Bangladesh, Bolivia and Argentina.

Since many countries are still affected by high levels of arsenic, we believe arsenic exposure is a global public health issue that requires urgent action. We study how exposure to toxic metals like arsenic can lead to cancer through the formation of cancer stem cells .

Arsenic contamination of food and water

Your body can absorb arsenic through several routes , such as inhalation and skin contact. However, the most common source of arsenic exposure is through contaminated drinking water or food.

People who live in areas with naturally high levels of arsenic in the soil and water are at particular risk. In the U.S., for example, that includes regions in the Southwest such as Arizona, Nevada and New Mexico. Additionally, human activities such as mining and agriculture can also increase arsenic in food and water sources.

High levels of arsenic can also be found in food and drink products , particularly rice and rice-based products like rice cereals and crackers. A 2019 Consumer Reports investigation even found that some brands of bottled water sold in the U.S. contained levels of arsenic that exceeded the legal limit. Alarmingly, multiple studies have also found that several popular baby food brands contained arsenic at concentrations much higher than the legal limit.

Arsenic and cancer stem cells

Chronic exposure to arsenic increases the risk of developing multiple types of cancer .

The mechanisms by which arsenic causes cancer are complex and not yet fully understood. However, research suggests that arsenic can damage DNA , disrupt cell signaling pathways and impair the immune system , all of which can contribute to cancer development.

Scientists have also linked chronic arsenic exposure to the development of cancer stem cells . These are cells within tumors thought to be responsible for cancer growth and spread. Like normal stem cells in the body, cancer stem cells can develop into many different types of cells. At what stage of cellular development a stem cell acquires the genetic mutation that turns it into a cancer stem cell remains unknown.

Our research aims to identify what type of cell arsenic targets to form a cancer stem cell. We are currently using cell cultures obtained from the same organ at different stages of cellular development to examine how the origins of cells affect the formation of cancer stem cells.

Preventing chronic arsenic exposure is critical to reducing the burden of arsenic-related health effects. Further research is needed to understand arsenic-induced cancer stem cell formation and develop effective strategies to prevent it. In the meantime, continued monitoring and regulation of this toxic metal in food and water sources could help improve the health of affected communities.

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Interaction of toxic metals in the digestive system revealed

NIEHS-funded researchers revealed how arsenic and cadmium may interact inside the human body, potentially altering their toxicity. The two metals frequently occur together in contaminated soil, but little is known about how combined exposure may affect health.

Using an simulated gastrointestinal (GI) tract in the lab, the team measured arsenic and cadmium bioaccessiblity, which is the amount of arsenic or cadmium that could be released during digestion and absorbed into the bloodstream. They exposed the artificial GI tract to cadmium only, arsenic only, or to a mixture of both metals. They also explored the effects of ferrihydrite, an iron mineral commonly found in dust, and pepsin, an enzyme responsible for protein digestion, to better replicate conditions inside the human body.

The team reported that cadmium bioaccessibility increased when arsenic was present. Arsenic bioaccessibility decreased with the addition of cadmium, but the arsenic present was transformed into a more toxic form. Both metals formed complexes with ferrihydrite, which promoted the release of cadmium but inhibited the release of arsenic. Pepsin formed soluble complexes with both metals, increasing their bioaccessibility.

According to the authors, these findings highlight the importance of understanding how exposure to contaminant mixtures affects their potential toxicity and may inform more protective regulatory strategies for soil and dust when cadmium and arsenic are both present.

Citation : Bai B, Kong S, Root RA, Liu R, Wei X, Cai D, Chen Y, Chen J, Yi Z, Chorover J. 2024. Release mechanism and interactions of cadmium and arsenic co-contaminated ferrihydrite by simulated in-vitro digestion assays . J Hazard Mater 467:133633.

Prenatal exposure to glyphosate linked to neurodevelopmental delays

An NIEHS-funded study found that glyphosate exposure during pregnancy may alter early brain development in children. According to the authors, this is one of the first studies to examine the relationship between exposure to the common herbicide before birth and neurodevelopment in young children.

The scientists studied 143 mother-baby pairs from Puerto Rico. To assess exposure, they collected urine samples from the mothers during pregnancy and measured levels of glyphosate and a common breakdown product of the herbicide. Then, they evaluated the children’s brain development at 6, 12, and 24 months using the Battelle Developmental Inventory. This test measures how well babies communicate, move, learn, and socialize. Using statistical models, they assessed potential links between the levels of glyphosate and the breakdown product in the mothers’ urine and their children’s performance on the test.

Children of mothers with higher glyphosate exposure scored lower in communication skills at 12 and 24 months. At 24 months, children with higher prenatal glyphosate exposure also scored lower in other areas, such as the ability to adapt to and understand new situations, attention, and memory.

These findings suggest that exposure to glyphosate during pregnancy may affect early neurodevelopment, with more pronounced delays by the time children reach 24 months, according to the authors. Because glyphosate is widely used, they noted that more research is needed to fully understand potential impacts on children’s neurodevelopment as they grow older.

Citation : Jenkins HM, Meeker JD, Zimmerman E, Cathey A, Fernandez J, Montañez GH, Park S, Pabón ZR, Vélez Vega CM, Cordero JF, Alshawabkeh A, Watkins DJ. 2024. Gestational glyphosate exposure and early childhood neurodevelopment in a Puerto Rico birth cohort . Environ Res 246:118114.

Maternal air pollution exposure, telomere length, and child sex interact to affect birthweight

NIEHS-funded researchers discovered that the length of a mother’s telomeres and the sex of her child complicate the effects of prenatal air pollution exposure on birthweight. Telomeres are regions of repetitive DNA sequences at the end of chromosomes that shorten with age. Several factors, including stress and exposure to environmental contaminants, can accelerate telomere shortening and biological aging.

The researchers explored whether premature aging of the placenta, reflected by telomere length, modifies the relationship between air pollution exposure and birthweight. Abnormal birthweight is associated with higher risk for health problems later in life. They looked at data from 306 mothers and their babies who participated in an urban health study in the Northeast U.S. Using mathematical models, the team assessed the effects of air pollution exposure during pregnancy and placental telomere length at delivery on birthweight while accounting for the length of the pregnancy and the baby’s sex.

Results differed by exposure window, air pollutant, sex, and placental telomere length. For boys, exposure to fine particulate matter during the third trimester was associated with lower birthweight if their mothers had longer telomeres. In contrast, exposure to ozone during the first trimester or nitrogen dioxide in the third trimester was associated with higher birthweight if mothers had shorter telomeres. For girls, exposure to a mix of pollutants during the second trimester was associated with lower birthweight if their mothers had longer placental telomeres.

According to the authors, the results suggest that exploring the complex relationships between exposure timing, air pollutant exposure, placental telomere length, and a baby’s sex may help researchers identify women at higher risk for adverse birth outcomes, informing targeted interventions.

Citation : Zhang X, Colicino E, Cowell W, Enlow MB, Kloog I, Coull BA, Schwartz JD, Wright RO, Wright RJ. 2024. Prenatal exposure to air pollution and BWGA Z-score: Modifying effects of placenta leukocyte telomere length and infant sex . Environ Res 246:117986.

Sorbent materials decrease movement and toxicity of PFAS in soil

A strategy developed by NIEHS-funded scientists may trap PFAS in soil and prevent the chemicals from spreading to plants or water. Immobilizing the chemicals in soil is one remediation strategy to reduce human exposure.

The scientists evaluated the ability of six different sorbent materials, made up of activated carbon or specialized clays, to trap four PFAS chemicals in soil. They measured how much PFAS solution leaked out of soil — a proxy for how much could be absorbed by plants or animals, called bioavailability — when each sorbent was added. They also explored how changes in PFAS bioavailability translated to toxicity by exposing worms and aquatic plants to soil or water following extraction.

Overall, adding any of the sorbent materials reduced PFAS bioavailability in soil by 58-97%. Activated carbon was the most effective at trapping PFAS, reducing the bioavailable amount by 73-97%, depending on the amount of sorbent used. Their method was effective in trapping PFAS for up to 21 days, even when the soil samples were exposed to different conditions, including simulations of acid rain, fresh water, and brackish water. Mirroring the reduced bioavailability of PFAS, the team reported a dose-dependent decrease in toxicity to plants and worms in the presence of any of the six individual sorbents — some modified clays promoted plant growth due to added nutrients.

According to the authors, adding a combination of activated carbon and modified clays is a practical approach to help reduce the spread of PFAS in soils while protecting surrounding plants and animals.

Citation : Wang M, Rivenbark KJ, Nikkhah H, Beykal B, Phillips TD. 2024. In vitro and in vivo remediation of per- and polyfluoroalkyl substances by processed and amended clays and activated carbon in soil . Appl Soil Ecol 196:105285.

(Adeline Lopez is a science writer for MDB Inc., a contractor for the NIEHS Division of Extramural Research and Training.)

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Silver-graphene oxide nanocomposite doping chitosan/PVA membrane for arsenic (III) elimination from aqueous solution

• Abd-Elghany, Amr A.
• Ramadan, Marwa A.
• El-Wakeel, Shaimaa T.
• AlOmari, Ahmad Khaleel
• Mohamad, Ebtesam A.

Heavy metals and pathogens from contaminated water sources may undoubtedly be removed by creating an efficient bio-adsorbent based on functional spots. Thus, the goal of this work was to produce chitosan (Ch)-polyvinyl alcohol (PVA) biofilm decorated with graphene oxide (GO) sheets doped with silver nanoparticles (AgNPs). The nanostructure of prepared GO/Ag nanosheets is examined by transmission electron microscope (TEM). The fabricated film (GO/Ag Ch-PVA) is compared by the control films (Ch, PVA and Ch-PVA). Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and tensile strength are used to study the films' structure. Also, the antimicrobial activity was assessed for the films. After doping the polymer matrix with GO/Ag, it was discovered that the tensile strength increased to about 46.18 MPa. Moreover, adsorption experiment for arsenic As (III) ions is explored by the prepared film at different operating conditions. The obtained results validated the enhanced adsorption ability of the GO/Ag Ch-PVA film towards As (III) with the highest adsorption capacity of 54.3 mg g ‑1 obtained from the isotherm model of Langmuir. Moreover, kinetic mathematical models for the adsorption effectiveness of GO/Ag Ch-PVA film are assessed. The results gathered demonstrated that GO/Ag Ch-PVA film is a potentially useful material for eliminating As (III) and microbial strains from essential water resources.

• graphene sheets;
• silver nanoparticles

• DOI: 10.17221/470/2023-pse
• Corpus ID: 270292359

Mitigation of arsenic toxicity in rice grain through soil-water-plant continuum

• O. R. Devi , Bibek Laishram , +7 authors Samiron Dutta
• Published in Plant, Soil and Environment 5 June 2024
• Environmental Science, Agricultural and Food Sciences

45 References

Potential use of arbuscular mycorrhizal fungi for simultaneous mitigation of arsenic and cadmium accumulation in rice., deficit irrigation and organic amendments can reduce dietary arsenic risk from rice: introducing machine learning-based prediction models from field data, arsenic behavior across soil-water interfaces in paddy soils: coupling, decoupling and speciation., health risk assessment of co-occurrence of toxic fluoride and arsenic in groundwater of dharmanagar region, north tripura (india), predicting the modifying effect of soils on arsenic phytotoxicity and phytoaccumulation using soil properties or soil extraction methods., arsenic retention in cooked rice: effects of rice type, cooking water, and indigenous cooking methods in west bengal, india., arsenic speciation dynamics in paddy rice soil-water environment: sources, physico-chemical, and biological factors - a review., arsenic accumulation in rice (oryza sativa l.) is influenced by environment and genetic factors., diffusive gradients in thin films reveals differences in antimony and arsenic mobility in a contaminated wetland sediment during an oxic-anoxic transition., arsenic accumulation in rice and probable mitigation approaches: a review, related papers.

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Effects of foliar spraying of dicarboxylicdimethylammonium chloride on cadmium and arsenic accumulation in rice grains.

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Fu, L.; Deng, J.; Lao, D.R.; Zhang, C.; Xue, W.; Deng, Y.; Luo, X. Effects of Foliar Spraying of Dicarboxylicdimethylammonium Chloride on Cadmium and Arsenic Accumulation in Rice Grains. Toxics 2024 , 12 , 418. https://doi.org/10.3390/toxics12060418

Fu L, Deng J, Lao DR, Zhang C, Xue W, Deng Y, Luo X. Effects of Foliar Spraying of Dicarboxylicdimethylammonium Chloride on Cadmium and Arsenic Accumulation in Rice Grains. Toxics . 2024; 12(6):418. https://doi.org/10.3390/toxics12060418

Fu, Lin, Jiawei Deng, Dayliana Ruiz Lao, Changbo Zhang, Weijie Xue, Yun Deng, and Xin Luo. 2024. "Effects of Foliar Spraying of Dicarboxylicdimethylammonium Chloride on Cadmium and Arsenic Accumulation in Rice Grains" Toxics 12, no. 6: 418. https://doi.org/10.3390/toxics12060418

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