Pilot-scale expanded assessment of inorganic and organic tapwater exposures and predicted effects in Puerto Rico, USA

Abstract

A pilot-scale expanded target assessment of mixtures of inorganic and organic contaminants in point-of-consumption drinking water (tapwater, TW) was conducted in Puerto Rico (PR) to continue to inform TW exposures and corresponding estimations of cumulative human-health risks across the US. In August 2018, a spatial synoptic pilot assessment of than 524 organic and 37 inorganic chemicals was conducted in 14 locations (7 home; 7 commercial) across PR. A follow-up 3-day temporal assessment of TW variability was conducted in December 2018 at two of the synoptic locations (1 home, 1 commercial) and included daily pre- and post-flush samples. Concentrations of regulated and unregulated TW contaminants were used to calculate cumulative in vitro bioactivity ratios and Hazard Indices (HI) based on existing human-health benchmarks. Synoptic results confirmed that human exposures to inorganic and organic contaminant mixtures, which are rarely monitored together in drinking water at the point of consumption, occurred across PR and consisted of elevated concentrations of inorganic contaminants (e.g., lead, copper), disinfection byproducts (DBP), and to a lesser extent per/polyfluoroalkyl substances (PFAS) and phthalates. Exceedances of human-health benchmarks in every synoptic TW sample support further investigation of the potential cumulative risk to vulnerable populations in PR and emphasize the importance of continued broad characterization of drinking-water exposures at the tap with analytical capabilities that better represent the complexity of both inorganic and organic contaminant mixtures known to occur in ambient source waters. Such health-based monitoring data are essential to support public engagement in source water sustainability and treatment and to inform consumer point-of-use treatment decision making in PR and throughout the US.

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

“…VOC remained a frequently detected class in public-supply TW locations, with predominantly xylenes observed in community C and xylenes and the fuel-oxygenate, t -butyl alcohol, systematically detected in community B. However, consistent with previous findings, 29 , 30 , 43 , 44 DBP dominated public supply organics, representing on average (median) 58% of detections and 92% of cumulative concentrations. Cumulative DBP concentrations were more than an order of magnitude higher ( p < 0.0001) in surface-water-sourced public-supply TW samples (community B only; median: 24.2 μg L –1 ) than in groundwater-sourced public-supply locations (median: 2.0 μg L –1 ) in communities B and C. Consistent with widespread agricultural use within Corn Belt drainage basins, 140 , 141 including the Missouri River basin, 142 pesticides (median: 6) were detected (concentrations ≤ 0.33 μg L –1 ) in every surface-water-sourced public-supply sample but were rarely detected in any groundwater-sourced location in this study.…”

“…These results indicate that simultaneous exposures to contaminants of human-health interest are common in both public- and private-supply TW locations across the study area. The bioactivity-weighted screening (Σ EAR and Σ TQ ) results ( Tables S10 and S13 ) indicate that exposures to DBP and inorganics at <MCL concentrations are the primary drivers of human-health interest in public-supply TW in communities B and C. These public-supply results align with the previous findings 29 , 30 , 43 , 44 and support the need for better understanding of exposure-effect relations and cumulative health risks of regulated/unregulated DBP 152 , 154 and for improved source-water pretreatment technologies to address DBP precursors, such as surface-water natural organic matter. 156 , 163 Exposures to As and U in groundwater-sourced drinking-water supplies have been reported previously in the study area and the concentrations observed in public-supply TW herein were below corresponding NPDWR MCL.…”

“…Common-place DBP-driven exceedance of HI screening-levels of concern in public-supply TW, in this study and previously, 29 , 30 , 43 , 44 reemphasize the public-health tradeoff of chlorine disinfection, 152 , 153 the importance of better understanding of the cumulative DBP health risks, 152 , 154 and the need for improved DBP-precursor (e.g., natural organic matter) removal prior to disinfection. 155 , 156 Likewise, frequent exceedances of the Σ TQ HI screening level of 0.1 in unregulated and generally unmonitored private-supply TW in this and previous studies 29 , 30 , 44 reiterate the inherent human-health challenge of unmonitored TW. 6 , 12 , 21 − 23 Simultaneous co-occurring inorganic and organic exposures and corresponding potentials for cumulative effects add weight to previous recommendations for systematic private-supply monitoring, 23 with an analytical scope that more realistically reflects the breadth of inorganic and organic environmental contamination.…”

“…Limited financial resources, water-quality expertise, and contaminant exposure data at the household scale fundamentally constrain private-supply decision-making and risk-mitigation options. 23 , 29 , 44 Analytically extensive datasets like this study, which are intended to inform scientific and public-health understanding of the role of drinking water as a vector for human contaminant exposures and associated human-health outcomes, remain limited because broad assessment of regulated and unregulated contaminants are not generally conducted at the TW point of exposure in the US or worldwide.…”

“… 29 , 30 , 43 , 44 As part of that ongoing effort, we assessed exposures to a broad suite of potential inorganic and organic TW contaminants in 56 homes in three areas of North Dakota and South Dakota in 2019 to provide insight into cumulative contaminant risk to human health 45 − 47 of private-well and small community public-supply TW in this region, to assess the utility of broader TW contaminant assessments for identifying additional risk management efficiencies in areas undergoing drinking-water interventions for As, and to expand the national perspective on inorganic and organic contaminant exposures at the TW point of use by maintaining the same general sampling protocol and analytical toolbox employed in previous studies. 29 , 30 , 43 , 44 …”