Inequalities in public water arsenic concentrations in counties and community water systems across the United States, 2006-2011
Background: In the US, nationwide estimates of public drinking water arsenic exposure are not readily available. We used the US Environmental Protection Agency’s (EPA) Six Year Review contaminant occurrence dataset to estimate public water arsenic exposure. We compared community water system (CWS) arsenic concentrations during (2006-2008) versus after (2009-2011) the initial monitoring period for compliance with EPA’s 10 µg/L arsenic maximum contaminant level (MCL). Our objective was to characterize potential inequalities in CWS arsenic exposure over time and across sociodemographic subgroups.
Methods: We estimated three-year average arsenic concentrations for 36,406 CWSs (98%) and 2,740 counties (87%) and compared differences in means and quantiles of water arsenic (via quantile regression) between both three-year periods for US regions and sociodemographic subgroups. We assigned CWSs and counties MCL compliance categories (High if above the MCL; Low if below) for each three-year period.
Results: From 2006-2008 to 2009-2011, mean and 95th percentile CWS arsenic (µg/L) declined by 10.3% (95% CI 14.1%, 6.5%) and 11.5% (14.8%, 8.3%) nationwide, by 11.4% (18.1%, 4.7%) and 16.3% (24.5%, 8.1%) for the Southwest, and by 36.8% (66.1%, 7.4%) and 26.5% (40.8%, 12.1%) for New England, respectively. CWSs in the High/High compliance category (not MCL compliant) were more likely in the Southwest (61.1%), served by groundwater (94.7%), serving smaller populations, and serving Hispanic communities (38.3%).
Discussion: Larger absolute declines in CWS arsenic concentrations at higher water arsenic quantiles indicate declines are related to MCL implementation. CWSs reliant on groundwater, serving smaller populations, located in the Southwest, and serving Hispanic communities were more likely to continue exceeding the arsenic MCL, raising environmental justice concerns. These estimates of public drinking water arsenic exposure at the county- and CWS-level can enable further surveillance and epidemiologic research, including assessing if differential declines in water arsenic exposure resulted in differential declines in arsenic-associated disease.
This code recreates the analysis published in Environmental Health Perspectives in December 2020.