Arsenic Drinking Water Violations Decreased Across the United States Following Revision of the Maximum Contaminant Level

Arsenic is the highest ranking substance on the Agency for Toxic Substances and Disease Registry’s Priority List due to its widespread environmental prevalence and known carcinogenic effects. While many industrial applications have ceased in the US, it is commonly found in hazardous waste sites and contributes to contamination of soil, waste streams, and water. Arsenic also exists in certain geologic formations where it can be released into the atmosphere and water from erosion, volcanic activity, and forest fires. The US EPA’s Toxics Release Inventory currently tracks industrial emissions of arsenic. In 2001, the EPA published the Final Arsenic Rule (FAR) for public drinking water, reducing the maximum contaminant level (MCL) from 50 g/L to 10 g/L. We investigated impacts of the FAR on drinking water violations temporally and geographically using the Safe Drinking Water Information System. Violations exceeding the MCL and the population served by violating systems were analyzed across the conterminous US from 2006 (onset of FAR enforcement) to 2017. The percentage of public water system violations declined from 1.3% in 2008 to 0.55% in 2017 (p < 0.001, slope= -0.070), and the population served decreased by over 1 million (p<0.001, slope = -106,886). Geographical analysis demonstrated higher mean violations and populations served were concentrated in certain counties rather than evenly distributed across states. The decline in violations is likely due to adoption of documented and undocumented treatment methods, and possibly from reduced environmental releases. Considering other studies have shown decreased urinary arsenic levels in the population served by public water systems since the new standard, it may be inferred that the FAR is facilitating reduction of arsenic exposure in the US.

Impact/Purpose

Research Translation or Community Engagement Narrative Chronic arsenic ingestion increases the risk of cancers and other health problems, so lowering levels in drinking water is an important public health intervention strategy. Today, far fewer public water systems have arsenic levels over 10 parts per billion than when the EPA first reduced the maximum contaminant level in 2001. The number of people served by systems in violation was also reduced by over 1 million. Other studies have found that urinary arsenic levels in US public water users declined during the same time period. This suggests that the new regulation has effectively reduced the amount of arsenic the US population is exposed to. Our study explored what factors may be driving these reductions, including changes to drinking water treatments and industrial emissions. Public water systems were less likely to be in violation if they reported arsenic-specific treatment. However, only a small proportion of violating systems that became compliant reported using treatment. This is likely due to underreporting of treatment within the Safe Drinking Water Information System. Improving the collection of data on treatment would benefit our understanding of how systems are best able to reach compliance. Industrial arsenic emissions also decreased during the time period, according to EPA’s Toxics Release Inventory (TRI). This could mean that there was less contamination into source waters, leading to fewer system violations. The reliability of TRI’s emission information has been questioned because of its self-reporting nature, However, further study linking contamination events in source water with TRI emissions data could help us to better understand how industrial emissions affect system compliance.

Citation

Foster, S., M. Pennino, J. Compton, S. Leibowitz, AND M. Kile. Arsenic Drinking Water Violations Decreased Across the United States Following Revision of the Maximum Contaminant Level. Superfund Research Program's annual meeting, Seattle, WA, November 18 - 20, 2019.