Arsenic is a naturally-occurring element that can leach into groundwater and surface water from rocks and minerals. In most areas, natural levels of arsenic in water are less than 1 ppb, though some communities, particularly in the Western U.S., have recorded natural arsenic levels in water sources over 10 ppb1. Arsenic can have both acute and chronic effects to human health4,5. The U.S. Environmental Protection Agency (EPA) has an extended history of promulgating arsenic regulations6. As of 2006, federal regulations require communities to meet a 10 ppb maximum contaminant level in drinking water supplies, which is difficult for many small communities7. To meet federal standards, communities require affordable treatment options.
In groundwater, arsenite [As(III)] and arsenate [As(V)], are of concern2. Most treatment options are applied to arsenate, so pre-treatment steps may include oxidation to transform As(III) to As(V)3. Techniques to remove arsenic by adsorption include activated carbon, activated alumina, coagulated floc using iron and other compounds, coral limestone, feldspar, and others3,8–10. Generally, arsenic adsorption increases as pH decreases; most media are designed to function in a low- to mid-pH range11. Activated carbon is popular for wastewater treatment, but it removes low fractional weights of arsenic per unit of media11. Activated alumina is more efficient and is effective for low pH values, though arsenites must still be pre-oxidized to arsenates before adsorption11,12. Iron-based compounds, including iron-coated materials, are also popular media13.
Arsenic removal presents particular problems for small and rural water supply systems. Advanced treatment options such as activated alumina are unaffordable or unavailable in many communities. For poorer communities affected by arsenic contamination in areas of Chile, Bangladesh, India, and Vietnam14–16, some research has examined alternative treatment options to reduce material costs, such as adsorption by water rice husks3. In such areas, central water supplies are often contaminated and household treatments are required. Research has reported arsenic removal from point-of-use devices using activated alumina and lower-cost media such as iron oxide-coated sand13. As communities seek regulatory compliance, cost-effective removal of arsenic will remain a challenge until treatment options become available that are affordable for both large and small systems.
Notably, arsenic in drinking water is not a new issue in the U.S. A decade ago, the Bush administration faced decisions regarding federal standards for arsenic in drinking water. More on that via Prezi:
Cover photo credit via safedrinkingwater.com/wordpress
1. Congressional Research Service Arsenic in Drinking Water: Regulatory Developments and Issues. (Washington, D.C., 2007).
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3. Amin, M. N. et al. Removal of Arsenic in Aqueous Solutions by Adsorption onto Waste Rice Husk. Industrial & Engineering Chemistry Research 45, 8105–8110 (2006).
4. World Health Organization Arsenic in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality. (2011).
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12. Massachussetts Department of Environmental Protection Arsenic in Private Well Water: Frequently Asked Questions. (2012).at <http://www.mass.gov/dep/water/drinking/arswell.htm>
13. Yuan, T., Hu, J. Y., Ong, S. L., Luo, Q. F. & Ng, W. J. Arsenic removal from household drinking water by adsorption. J Environ Sci Health A Tox Hazard Subst Environ Eng 37, 1721–1736 (2002).
14. Anawar, H. M., Akai, J., Mostofa, K. M. G., Safiullah, S. & Tareq, S. M. Arsenic poisoning in groundwater: Health risk and geochemical sources in Bangladesh. Environment International 27, 597–604 (2002).
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