Worldwide Occurrences of Arsenic in Ground Water

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Science  21 Jun 2002:
Vol. 296, Issue 5576, pp. 2143-2145
DOI: 10.1126/science.1072375

As the world population increases beyond 6 billion, one of the most fundamental resources for human survival, clean water, is decreasing. Revised estimates from the World Health Organization for 1990 indicate that 43% of the world's population do not have adequate sanitation and 22% do not have clean drinking water [HN1] (1, 2). The rising demands for sanitary water often cannot be met by surface-water supplies. This has led to increased dependence on ground-water [HN2] resources in many parts of the world. The consequences of ground-water development often include overdrafting, land subsidence, and the use of ground water unfit for human consumption. The recent increased utilization of ground water in India and Bangladesh has caused new health issues (35). An estimated 36 million people in the Bengal Delta are at risk from drinking arsenic-contaminated water [HN3]. Numerous other occurrences worldwide have been reported (see table, below) (6), and some of these, such as those in Taiwan, have been recognized for several decades [HN4].

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Arsenic [HN5] is not found in high abundance in the Earth's continental crust; it is less abundant than several of the “rare-earth” elements (7). Unlike the rare-earth elements, however, arsenic is commonly concentrated in sulfide-bearing mineral deposits, especially those associated with gold mineralization, and it has a strong affinity for pyrite (8), one of the more ubiquitous minerals in the Earth's crust. It is also concentrated in hydrous iron oxides. Arsenic can be easily solubilized in ground waters depending on pH, redox conditions, temperature, and solution composition [HN6] (6). Many geothermal waters contain high concentrations of arsenic (9). Natural arsenic in ground water at concentrations above the drinking water standard of 10 μg/liter is not uncommon. Man-made sources of arsenic, such as mineral extraction and processing wastes, poultry and swine feed additives, pesticides, and highly soluble arsenic trioxide stockpiles are also not uncommon and have caused the contamination of soils and ground waters.

A small number of source materials are now recognized as significant contributors to arsenic in water supplies: organic-rich or black shales, Holocene alluvial sediments with slow flushing rates, mineralized and mined areas (most often gold deposits), volcanogenic sources, and thermal springs. The relationship between high arsenic concentrations and geothermal waters is not a simple one. Arsenic concentrations are high in the thermal waters of Kamchatka, New Zealand, Japan, Alaska, California, and Wyoming, where black shales are common, but they are low in thermal waters from Hawaii and Iceland (10), where most of the rocks are geologically young basalts. Aquifers with carbonaceous shales and without obvious thermal gradients, such as in Taiwan, also can lead to high dissolved arsenic concentrations.

Two other environments can lead to high arsenic: (i) closed basins in arid-to-semi-arid climates (especially in volcanogenic provinces) and (ii) strongly reducing aquifers, often composed of alluvial sediments but with low sulfate concentrations. Young sediments in low-lying regions of low hydraulic gradient are characteristic of many arsenic-rich aquifers. Ordinary sediments containing 1 to 20 mg/kg (near crustal abundance) of arsenic can give rise to high dissolved arsenic (> 50 μg/liter) if initiated by one or both of two possible “triggers”—an increase in pH above 8.5 or the onset of reductive iron dissolution (6). Potentially important, additional factors promoting arsenic solubility are high concentrations of phosphate, bicarbonate, silicate, and/or organic matter in the ground waters. These solutes can decrease or prevent the adsorption of arsenate and arsenite [HN7] ions onto fine-grained clays, especially iron oxides. Arsenite tends to adsorb less strongly than arsenate often causing arsenite to be present at higher concentrations. Unfortunately, these generalities do not allow prediction of high or low dissolved arsenic concentrations in any particular well because of heterogeneous distributions in the aquifers. Furthermore, arsenic concentrations can change in any given well over the course of a few years so that regular monitoring is required in high-risk areas (11).

In a number of areas worldwide, oxidation and dissolution of arsenian pyrite, Fe(As,S)2, and arsenopyrite [HN8], FeAsS, are additional processes that lead to high concentrations of dissolved arsenic (12). The oxidation can be promoted naturally through infiltrating oxygenated ground waters (13) or through lowering of the ground-water table (by well-water pumping or climate variations) into a stratigraphic zone containing arsenic-rich sulfides (14). The highest natural arsenic concentrations found in the United States (1 to 10 mg/liter) are in the Fairbanks, Alaska [HN9], area, where arsenopyrite-rich zones in igneous and metamorphic rocks are being oxidized, and there may also be some iron reduction (13).

The key to minimizing risk is to incorporate hydrogeological, geochemical, and microbiological expertise into the decision-making process of water managers, remediation specialists, and policy-makers. The geologic and ground-water conditions that promote high arsenic concentrations are known and can help identify high-risk areas. The western United States has many ground waters where arsenic is found in concentrations > 10 μg/liter, and treating them will be expensive but may be trivial compared with potential health-care costs. In the search for adequate water supplies and in the absence of adequate information, it is prudent to test selected wells before opening the tap.

HyperNotes Related Resources on the World Wide Web

General Hypernotes

This issue of Science has a related Enhanced Policy Forum by A. H. Smith et al. titled “Arsenic epidemiology and drinking water standards.”

Dictionaries and Glossaries

A chemistry and environmental dictionary is provided by EnvironmentalChemistry.com.

A glossary of water quality terms is provided by the Center for Environmental Quality, Wilkes University, Wilkes-Barre, PA.

A multilingual glossary of environmental terms is provided by the European Environment Agency.

The International Glossary of Hydrology is made available by P. Hubert, Centre d'Informatique Géologique, Fontainebleau, France.

Web Collections, References, and Resource Lists

The Open Directory Project provides links to Internet resources on Earth sciences and on the environment with a section on water resources.

The WWW Virtual Library: Environment is maintained by Earthsystems.org.

The World's Water Web site provides links to Internet resources on global freshwater resources.

Water Links Worldwide are provided by the Water Portal of the United Nations Educational, Scientific and Cultural Organization (UNESCO).

MedLine Plus provides links to arsenic information resources.

Online Texts and Lecture Notes

The Water and Sanitation Division of the World Health Organization (WHO) offers resources on water-related topics. A resource page on arsenic in drinking water is included.

The Toxic Metals Research Program, Dartmouth College, offers a metals primer with a presentation on arsenic and a history of arsenic. A collection of Internet links related to toxic metals is also provided.

Chronic Arsenic Poisoning: History, Study and Remediation is an Arsenic Project Web resource provided by R. Wilson, Department of Physics, Harvard University. A collection of Internet links is included.

The Supercourse on Health, Environment and Sustainable Development Web site makes available lectures on arsenic by M. Azad, Department of Nutrition and Biochemistry, University of Bangladesh.

Fundamentals of Physical Geography, an online text by M. Pidwirny, Department of Geography, Okanagan University College, Kelowna, BC, Canada, includes a section on hydrology.

R. Foust, Department of Chemistry, Northern Arizona University, offers lecture notes for a course on environmental chemistry.

D. Sherman, Department of Earth Sciences, University of Bristol, UK, offers lecture notes (in PDF format) and tutorials for a course on environmental geochemistry.

J. Moore, Department of Geology, University of Montana, offers lecture notes for an environmental geochemistry course. A presentation on natural high arsenic systems is included.

General Reports and Articles

The United Nations Synthesis Report on Arsenic in Drinking Water is made available by the WHO Water and Sanitation Division. Included is a chapter on the source and behavior of arsenic in natural waters.

The National Academy Press makes available the National Research Council (NRC) reports Arsenic in Drinking Water (1999) and Arsenic in Drinking Water: 2001 Update. The 1999 report includes a chapter on the chemistry and analysis of arsenic species in water and biological materials.

Numbered Hypernotes

1. The world's clean water resources. The WHO Water and Sanitation Division makes available the Global Water Supply and Sanitation Assessment 2000 Report. The February 1999 issue of the UNESCO Courier had a special report on water resources. The February 2001 issue of Scientific American had an article by P. Gleick titled “Making every drop count.” World Water Crisis is a presentation of BBC News, which also makes available a 22 March 2002 article titled “UN warns of looming water crisis.” The University of Michigan's Global Change Program makes available lecture notes on human appropriation of the world's fresh water supply.

2. Ground water. The Groundwater Foundation offers a Groundwater Basics Web page and a glossary of groundwater-related terminology. The USGS offers an introduction to ground water and a ground water information resource collection. A ground water primer is made available by the EPA's Software for Environmental Awareness Web site.

3. Arsenic contamination in the Bengal Delta. WHO provides a fact sheet on arsenic in drinking water. The West Bengal and Bangladesh Arsenic Crisis Information Centre (ACIC) provides news articles, scientific papers, and links related to arsenic poisoning of Bangladesh groundwater. ACIC makes available an article (published 24 September 1998 in Nature) by R. Nickson et al. titled “Arsenic poisoning of Bangladesh groundwater” (5) and a special issue on arsenic of the newsletter of the Bangladesh Centre for Advanced Studies. Arsenic Calamity of Bangladesh is a Web resource provided by Engconsult Limited, Toronto, Canada. The Asia Arsenic Network makes available a newsletter article by S. Tsushima titled “Arsenic contamination in ground water in Bangladesh: An overview.” The September 2000 issue of the Bulletin of the World Health Organization had an article (available in PDF format) by A. Smith, E. Lingas, and M. Rahman titled “Contamination of drinking-water by arsenic in Bangladesh: A public health emergency.” The January 2001 issue of the UNESCO Courier had an article by F. Pearce titled “Bangladesh's arsenic poisoning: Who is to blame?” The Harvard School of Public Health provides information about the Bangladesh arsenic project. BBC News makes available an 8 February 1998 article titled “Contaminated water affects millions in Bangladesh,” a 27 March 1998 article titled “Poisoned water endangers millions,” a 10 January 1999 article titled “Bangladesh arsenic crisis, and a 6 October 1999 article titled “Poison threat in Bangladesh.”

4. Other occurrences worldwide. The United Nations Synthesis Report on Arsenic in Drinking Water includes a section on world distribution of groundwater arsenic problems in the chapter on the source and behavior of arsenic in natural waters. R. Wilson's Arsenic Project Web site includes a presentation on arsenic problems in countries of the world. The Asia Arsenic Network offers a presentation on arsenic contamination in Asia with a section on Taiwan.

5. Arsenic. WebElements provides information about arsenic. The Mineral Galley has an entry for arsenic. Arsenic was selected as a Chemical of the Week by B. Shakhashiri, Department of Chemistry, University of Wisconsin. The Environmental Contaminants Encyclopedia, made available (in PDF format) by the U.S. National Park Service, includes a detailed entry for arsenic. The INCHEM Web site from the International Program on Chemical Safety provides information on arsenic. The National Toxicology Program makes available a summary on arsenic and arsenic compounds. The U.S. Agency for Toxic Substances and Disease Registry provides a fact sheet on arsenic and a toxicological profile for arsenic.

6. Arsenic in ground water and arsenic geochemistry. The British Geological Survey provides a Web page about arsenic contamination of groundwater with background information and presentations on the survey's investigations in Bangladesh. The USGS Water Resources Division offers a resource page on arsenic in ground water of the United States; a section on the sources of arsenic in ground water is included in a conference paper by A. Welch et al. titled “Arsenic in ground water supplies of the United States.” The arsenic Web site provided by B. Merkel, Hydrogeology Group, Technische Universität Bergakademie, Freiberg, Germany, includes a section on arsenic chemistry. A section on the geochemistry of arsenic is provided in a USGS report titled “Arsenic in ground water of the Willamette Basin, Oregon.” The 1997 report Arsenic: Medical and Biological Effects of Environmental Pollutants, available from the National Academy Press, includes chapters on the chemistry of arsenic and arsenic distribution in the environment. Water Environment International makes available an article (in PDF format) by R. Nickson et al. titled “Mechanism of arsenic poisoning of groundwater, Bangladesh and West Bengal,” which was published in Applied Geochemistry (vol. 15, p. 403, 2000).

7. Arsenates and arsenites. Arsenate and arsenite are defined in the Dictionary of Mining, Mineral, and Related Terms. The Mineral Gallery offers a presentation on arsenates and arsenites. A section on arsenates and arsenites is included in the chemistry chapter of the 1977 report Arsenic: Medical and Biological Effects of Environmental Pollutants. The IPCS INCHEM Web site makes available a report on inorganic arsenic compounds.

8. Arsenopyrite is defined in the Dictionary of Mining, Mineral, and Related Terms. The Mineral Gallery has an entry for arsenopyrite. The Mineralogy Database has an entry for arsenopyrite and the arsenopyrite group. The USGS Arsenic Studies Group offers a presentation on arsenic minerals.

9. Arsenic concentrations in the Fairbanks area. The USGS makes available a fact sheet (in PDF format) titled “Ground-water studies in Fairbanks, Alaska—A better understanding of some of the United States' highest natural arsenic concentrations.” The USGS Arsenic Studies Group makes available (in PDF format) a paper by S. H. Mueller et al. titled “A seasonal study of the arsenic and groundwater geochemistry in Fairbanks, Alaska” from a USGS Workshop on Arsenic in the Environment.

10. D. K. Nordstrom is in the Water Resources Division, U.S. Geological Survey, Boulder.

References and Notes

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