UNCORRECTED PROOFS Henke c06.tex V1 - 12/09/2008 4:19 P.M. Page 1 6 Major Occurrences of Elevated Arsenic in Groundwater and Other Natural Waters ABHIJIT MUKHERJEE 1 , ALAN E. FRYAR 2 , and BETHANY M. O’SHEA 3 1 Bureau of Economic Geology, University of Texas at Austin 2 University of Kentucky, Department of Earth and Environmental Sciences 3 Columbia University, Lamont-Doherty Earth Observatory, Geochemistry Division 6.1 Introduction Arsenic contamination of drinking water is a serious and widespread problem. [(Smedley and Kinniburgh, 2002), 520] remarked that ‘As and F are now recognized as the most serious inorganic contaminants in drinking water on a worldwide basis’, yet arsenic was not routinely analyzed by water-quality laboratories until within the last two decades. The World Health Organization (WHO) has recommended a maximum arsenic concentration of 10 μgl −1 in drinking water and this value has been adopted, at least provisionally, as a regulatory standard by the European Union, the United States, Japan, and many other nations ((Smedley and Kinniburgh, 2002), Appendix E). However, the former WHO and United States limit of 50 μgl −1 remains the standard in many developing countries, in part because of financial and analytical limitations in measuring lower concentrations ((Smedley and Kinniburgh, 2002), Appendix E). Significant clusters of chronic illnesses associated with arsenic ingestion have been reported from Bangladesh, India, Taiwan, Chile, and Argentina. In these and other locations, exposure frequently results from drinking groundwater containing elevated concentrations of naturally occurring (geogenic) arsenic. This chapter focuses on cases of severe and extensive arsenic contamination of groundwater at various locations around the world. With the exception of mining, the discussions include instances in which human activities have induced or exacerbated the contamination. Very localized cases of groundwater pollution resulting from the use of arsenical compounds (such as pesticides) or arsenic-contaminated products are Arsenic Edited by Kevin R. Henke c  2009 John Wiley & Sons, Ltd 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47