Cancer Risks Associated with Elevated Levels of Drinking Water Arsenic Exposure

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In 2001 the U.S. Environmental Protection Agency (EPA) reduced the maximum contaminant level (MCL) for arsenic in drinking water from 50 µg/L to 10 µg/L, with the new MCL to take effect in 2006. This new MCL affects many U.S. community water systems located in areas of the country with high naturally-occurring arsenic in surface and ground water. Because of the expense of removing arsenic and the large number of systems affected, the costs of compliance with the new standard will place an economic burden on many small communities. EPA estimates that implementation of the revised arsenic standard will prevent between 6.9 and 33 bladder and lung cancer deaths each year. Recent epidemiological studies in Argentina and the United States, however, raise questions about the scientific justification for the revised arsenic MCL. In addition, although recent studies have failed to detect expected arsenic-related cancer risks, there are indications that EPA intends to further lower the arsenic MCL to below 10 µg/L. Several states, including California and New Jersey, have already begun the process of lowering their arsenic MCL to below 10 µg/L and California is considering implementing a standard below 1 µg/L (1 part per billion). This study identified U.S. counties in which the mean drinking water arsenic level was 10 µg/L or greater during 1950-1999. We conducted a multi-level, hierarchical analysis of county standardized mortality ratios (SMRs) and standardized incidence ratios (SIRs). The objective of this study was to examine whether lung and bladder cancer incidence or mortality rates are elevated in United States populations consuming drinking water that exceeds the new EPA MCL for arsenic