Socioeconomic Disparities in Exposures to PFAS and Other Unregulated Industrial Drinking Water Contaminants in US Public Water Systems.

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Unregulated contaminants in drinking water, such as per- and polyfluoroalkyl substances (PFAS), can contribute to cumulative health risks, particularly in overburdened and less-advantaged communities. To our knowledge, there has been no nationwide assessment of socioeconomic disparities in exposures to unregulated contaminants in drinking water. The goals of this study were to identify determinants of unregulated contaminant detection among US public water systems (PWSs) and evaluate disparities related to race, ethnicity, and socioeconomic status. We gathered data from the US Environmental Protection Agency's (US EPA's) Third Unregulated Contaminant Monitoring Rule (2013-2015), PWS characteristics, sociodemographic data, and suspected pollution sources from regulatory databases. We included four target contaminants (or classes) with industrial sources: PFAS, 1,4-dioxane, 1,1-dichloroethane, and chlorodifluoromethane (HCFC-22). Associations were evaluated with pairwise comparison tests and generalized logistic mixed-effects regression models for six dichotomous outcomes: detection of each of four target contaminants, detection of target contaminant, and PWS exceedance of US EPA health reference level that was in effect in 2017. More than 97 million US residents were served by a PWS with detectable levels of 1,4-dioxane (22% of PWSs), HCFC-22 (5.8%), 1,1-dichloroethane (4.7%), and/or PFAS (4.0%). Unregulated contaminant detection was more frequent among large systems, urban systems, and systems using groundwater or a combination of groundwater and surface water. In comparison with PWSs with no detectable levels of these unregulated contaminants, PWSs with detectable levels served counties with higher proportions of Hispanic residents (17% vs. 13%), as did PWSs that exceeded EPA health reference levels in comparison with PWSs with no exceedances (18% vs. 14%). There were persistent positive associations between proportions of Hispanic residents and detections of target contaminants, even after accounting for pollution sources. Previously, inequities in exposures to drinking water contaminants were underestimated because prior studies have focused on regulated contaminants. PWSs serving counties with more Hispanic residents, non-Hispanic Black residents, and urban households may benefit from additional resources to proactively mitigate unregulated chemical contamination. Future studies should evaluate factors underlying these disparities to promote actions that protect water quality for all residents. https://doi.org/10.1289/EHP14721.