Tapwater Exposures, Effects Potential, and Residential Risk Management in Northern Plains Nations

In the United States (US), private-supply tapwater (TW) is unregulated Federally and rarely monitored. This data gap undermines individual and community risk management decision making, leading to increased probability of unrecognized contaminant exposures in rural and remote locations that rely on private wells. We assessed point-of-use (POU) TW in three Northern Plains Tribal Nations, where ongoing TW arsenic (As) interventions include expansion of small community water systems and POU adsorptive-media treatment for remote homes participating in the ongoing Strong Heart Water Study. TW samples from 34 private-well and 22 public-supply sites were analyzed for 3 field parameters, 476 organics, 34 inorganics, and 3 in vitro bioactivities. Health benchmark weighted cumulative Hazard Indices (HI) and ratios of organic ontaminant in vitro exposure-activity cutoffs were assessed for detected contaminants. Sixty-three organics and 30 inorganics were detected in TW. Arsenic, uranium (U), and lead (Pb) were detected in 54%, 43%, and 20% of samples, respectively. Concentrations equivalent to public supply Maximum Contaminant Level(s) (MCL) were exceeded only in untreated private-well samples (As 47%, U 3%). Precautionary health based HI screening levels were exceeded frequently and attributed primarily to inorganics in private supplies and chlorine-based disinfection byproducts (DBP) in public supplies. The results support ongoing interventions to reduce TW As exposures and indicate that simultaneous exposures to other co-occurring TW contaminants are common, warranting consideration of expanded source, point-of-entry (POE), or POU treatment(s). This study supports the need for increased monitoring of private-well TW employing a broad, environmentally informative analytical scope to reduce the risks of unrecognized contaminant exposures and to identify possible additional targets for simultaneous TW risk mitigation (e.g., U, Pb, DBP in this study).

Impact/Purpose

The current imbalance of information on drinking-water contaminant exposure and associated risks between private- and public tapwater supplies contributes to data-poor consumer decisions, including delayed transition to monitored public supplies or adoption of appropriate point-of-use treatment in rural and other high risk locations. The U.S. Geological Survey continues to collaborate with the USEPA, NIEHS, Colorado School of Mines, Tribes, and others to fill drinking-water exposure data gaps in a range of source-water vulnerability settings. The current Strongheart cohort study and others across the US provide a standardized, broad characterization of inorganics and organics to help address the data gap on mixed contaminant exposures in US residential TW and to inform public-health research assessments of the importance of drinking water contaminant exposures as drivers of human health outcomes.

Citation

Bradley, P., E. Medlock Kakaley, K. Romanok, K. Smalling, M. Focazio, R. Charboneau, C. George, A. Navas-Acien, M. O'Leary, R. Red Cloud, T. Zacher, S. Breitmeyer, M. Cardon, C. Cuny, G. Ducheneaux, K. Enright, N. Evans, J. Gray, D. Harvey, M. Hladik, K. Loftin, R. McClesky, S. Meppelink, J. Valder, C. Weiss, AND L. White. Tapwater Exposures, Effects Potential, and Residential Risk Management in Northern Plains Nations. American Chemical Society, Washington, DC, 2(10):1772-1788, (2022). [DOI: 10.1021/acsestwater.2c00293]

DOI: Tapwater Exposures, Effects Potential, and Residential Risk Management in Northern Plains Nations