Ravalli et al. 2022 — Uranium and metal inequalities in US community water systems
This large cross-sectional study estimated concentrations of ten metals in community water systems (CWSs) serving ~290 million Americans, using US EPA compliance monitoring records from 2006–2011 (2000–2011 for uranium). Uranium emerged as an under-recognized drinking water contaminant with the highest detection rate (63.1%) of all metals examined; 2.1% of CWSs exceeded the EPA MCL of 30 µg/L. Arsenic exceeded its MCL (10 µg/L) in 2.6% of CWSs. Elevated concentrations of uranium, chromium, barium, and selenium were concentrated in CWSs serving Semi-Urban Hispanic communities and CWSs relying on groundwater in the Central Midwest, highlighting environmental justice concerns.
Key numbers
Total CWSs analyzed: 37,915. Metals examined: antimony, arsenic, barium, beryllium, cadmium, chromium, mercury, selenium, thallium, uranium. Main analysis (>10% detection): arsenic, barium, chromium, selenium, uranium. Total monitoring records: ~297,000 (As), ~165,000 (Ba), ~167,000 (Cr), ~165,000 (Se), ~128,000 (U).
Detection rates above LOD: As 45.5%, Ba 60.8%, Cr 18.9%, Se 12.9%, U 63.1%. Low detection: Sb 2.2%, Be 1.3%, Cd 1.6%, Hg 1.5%, Tl 1.6%.
Nationwide means and MCL exceedances: As nationwide mean 1.77 µg/L (MCL 10 µg/L); 2.6% of CWSs exceeded the MCL (n=36,798 CWSs). U nationwide mean 4.37 µg/L (MCL 30 µg/L); 2.1% of CWSs exceeded the MCL (n=14,503 CWSs). Ba, Cr, Se: less than 0.1% exceeded their respective MCLs.
75th and 95th percentile concentrations for uranium, chromium, barium, and selenium were highest in CWSs serving Semi-Urban Hispanic communities, CWSs using groundwater, and CWSs in the Central Midwest. Hierarchical cluster analysis identified two distinct clusters: an arsenic-uranium-selenium cluster and a barium-chromium cluster.
Methods (brief)
US EPA SYR2 (2000–05) and SYR3 (2006–11) compliance monitoring databases. Non-detect values replaced by LOD/√2 per CDC convention. CWS-level averages computed by calendar year then averaged over the 6-year period. Subgroup analysis by: source water type, population served, region, CWS serving correctional facilities, and sociodemographic county-cluster. Non-parametric Kruskal-Wallis tests for subgroup comparisons; quantile regression for uranium-Hispanic association adjusting for state, population size, and water source type. R version 3.5.3.
Implications
Certification: Uranium in US drinking water at concentrations above 30 µg/L in 2.1% of CWSs is directly relevant to the HMT&C framework for setting context around drinking water contribution to total U exposure. This study is the first nationwide systematic characterization of multiple metals simultaneously in US public water, providing baseline distributional context for the wiki’s regulations layer.
Courses: Foundational for teaching environmental justice dimensions of heavy metal exposure in drinking water. Demonstrates that regulatory compliance does not eliminate population-level inequalities.
App: Uranium is an under-recognized dietary exposure route via drinking water; the app should flag U in drinking water for populations in the Central Midwest and Southwest US. Arsenic MCL exceedance rate (2.6% of CWSs) confirms that a non-trivial minority of US consumers have drinking water As above regulatory limits.