ABSTRACT: In the United States (US), private-supply tapwater (TW) is 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 contaminant 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).

This dataset is associated with the following publication: Bradley, P.M., E. Medlock Kakaley, K.M. Romanok, K. Smalling, M. Focazio, R. Charboneau, C.M. George, A. Navas-Acien, M. O'Leary, R. Red Cloud, T. Zacher, S.E. Breitmeyer, M. Cardon, C. Cuny, G. Ducheneaux, K. Enright, N. Evans, J.L. Gray, D.O. Harvey, M.L. Hladik, K.A. Loftin, R.B. McClesky, S. Meppelink, J.F. Valder, C.P. Weiss, and L. White. Tapwater Exposures, Effects Potential, and Residential Risk Management in Northern Plains Nations. ACS ES&T Water. American Chemical Society, Washington, DC, USA, 2(10): 1772-1788, (2022).