No abstract

Per-and polyfluoroalkyl substances (PFAS) in U.S. drinking water are currently a significant topic of public health concern. Data collection efforts have been undertaken to better understand PFAS occurrence, though limited data observed above reporting limits leaves considerable uncertainty. This work presents a hierarchical Bayesian model developed to estimate national PFAS occurrence in drinking water with a simple model structure and assumptions.Here the model is limited to the occurrence of perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS), and perfluoroheptanoic acid (PFHpA). This model estimates national PFAS exposure while capturing uncertainty, provides information on system-level PFAS co-occurrence, and creates an expandable foundation for generating future national estimates of PFAS occurrence. National estimates based on currently available data and model assumptions indicated population-weighted mean exposure to the sum of mean PFOS, PFOA, PFHpA, and PFHxS around 4.7-5.2 ppt while all four chemicals generally had moderate-to-strong correlations among system-level means.

During a cyanobacterial harmful algal bloom (HAB) event, drinking water treatment systems face the challenge of balancing acute and chronic health risks by treating the potentially toxin‐producing HAB and simultaneously managing for disinfection byproduct (DBP) formation. To explore the relationship between HAB events and DBP formation, a unique full‐scale study, including paired source water and finished water monitoring, was conducted at five drinking water utilities with HAB‐impacted source waters. Results confirm bench‐scale findings that HAB events in source water contribute to increases in DBP precursors. However, unlike results from laboratory studies, source water HAB‐related parameters and finished water DBPs were not consistently correlated at the five study utilities. These different outcomes suggest regulated DBP formation in utilities with HAB‐impacted source water is complex and influenced by a variety of site‐specific conditions, including source water conditions and data available for operational decision‐making, timing of treatment adjustments, and key operational choices.

Bromide concentrations have been changing in rivers in Pennsylvania. Elevated bromide in source waters at drinking water treatment plant intake locations is expected to increase the formation and bromine incorporation of disinfection by-products (DBPs) that present health risks to consumers. Results from major drinking water distribution systems in southwestern and southeastern Pennsylvania taken during a national sampling effort (1997-1998) were compared with more recent data from these same systems (2012-2016). Sample sets were compared both temporally, across the nearly 20-year span between the first and final sampling periods, and spatially, comparing southwestern and southeastern Pennsylvania. Total trihalomethanes (TTHM) and bromine incorporation data show little change in southeastern Pennsylvania. In southwestern Pennsylvania, TTHM decreased significantly, likely as a result of treatment modifications designed to comply with more stringent regulations. However, fractional bromine incorporation in THMs increased, indicating TTHM reductions were associated with reduced chloroform alone. Risk metrics prioritizing brominated species indicated no change in southwestern Pennsylvania despite the decline in the surrogate, TTHM, which is used for regulatory compliance.