Predictions of PFAS regional-scale atmospheric deposition and ambient air exposure

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a large class of human-made compounds that have contaminated the global environment. One environmental entry point for PFAS is via atmospheric emission. Air releases can impact human health through multiple routes, including direct inhalation and contamination of drinking water following air deposition. In this work, we convert the reference dose (RfD) underlying the United States Environmental Protection Agency's GenX drinking water Health Advisory to an inhalation screening level and compare to predicted PFAS and GenX air concentrations from a fluorochemical manufacturing facility in Eastern North Carolina. We find that the area around the facility experiences ~15 days per year of GenX concentrations above the inhalation screening level we derive. We investigate the sensitivity of model predictions to assumptions regarding model spatial resolution, emissions temporal profiles, and knowledge of air emission chemical composition. Decreasing the chemical specificity of PFAS emissions has the largest impact on deposition predictions with domain-wide total deposition varying by as much as 250 % for total PFAS. However, predicted domain-wide mean and median air concentrations varied by <18 % over all scenarios tested for total PFAS. Other model features like emission temporal variability and model spatial resolution had weaker impacts on predicted PFAS deposition.

Keywords: Air quality; Community multiscale air quality (CMAQ) model; Emissions; Modeled ambient concentrations; Per- and polyfluoroalkyl substances (PFAS).

Figure 1.

Fraction of the year that the grid cells containing the facility, Fayetteville, and Wilmington, are below the PM PFAS measurement detection limit (gray), above the GenX ISL of 7.5 ng m⁻³ (yellow), and between these two values (green). The GenX PM MDL is 0.017 pg m⁻³, and the total PFAS MDL is 0.005 pg m⁻³. Due to rounding, some percentages do not add to 100.

Figure 2.

The impact of temporal allocations on domain-wide cumulative deposition. A) Cumulative domain-wide deposition of total PFAS by month for the different emissions allocation scenarios. B) Cumulative domain-wide deposition of GenX (HFPO-DA + HFPO-DAF) by month.

Figure 3.

The percent of annual PFAS emissions deposited via wet (blue) and dry (gray scale) deposition within the domain, i.e within ~150 km of the facility, for each of the model scenarios tested herein.