Insights from Modeling the Fate of and Exposure to Persistent and Mobile Organic Chemicals using the Refined PROTEX Model.

Persistent and mobile (PM) organic chemicals have been recognized as a threat to aquatic environments and drinking water quality due to their potential to infiltrate natural barriers and contaminate various sources of drinking water. Here, we refine a multimedia mass-balance model named PROduction-To-EXposure (PROTEX) to support evaluating the environmental fate of and human exposure to PM organic chemicals in different sources of drinking water. By examining a case study chemical, perfluorooctanoic acid (PFOA), we demonstrate that the multimedia transport and distribution of PM organic chemicals in a region is influenced by both the mode of emission (ie, the environmental medium/media into which a chemical is initially released) and the source of drinking water (ie, the water medium from which it is extracted). As our modeling results indicate, in humid regions, regionally released PFOA predominantly accumulates in estuarine water, potentially reaching open seas and oceans. In contrast, in arid regions, a remarkable portion of regionally released PFOA may concentrate in deep groundwater. Compared to other scenarios, contamination by PM organic chemicals is likely to be significantly less reversible when these substances are released into deep groundwater, or when drinking water is sourced from deep groundwater. In these cases, contamination may not reach a steady state within a century-scale timeframe, and dynamic modeling informed by temporal emission trends is appropriate for assessment. Our work provides a computational tool for evaluating the large numbers of chemicals on the market for their potential to impact drinking water safety. It also underscores the need to consider the mode of emission and the source of drinking water to achieve fit-for-purpose assessments of PM organic chemicals.