Legacy and Emerging Perfluoroalkyl Substances Are Important Drinking Water Contaminants in the Cape Fear River Watershed of North Carolina

TLDR

Long‑chain per‑ and polyfluoroalkyl substances (PFASs) are being replaced by short‑chain PFASs and fluorinated alternatives. The study reports the occurrence, fate in water‑treatment processes, and adsorbability on powdered activated carbon of ten legacy PFASs and seven newly discovered perfluoroalkyl ether carboxylic acids (PFECAs) in the Cape Fear River watershed. The authors measured concentrations of these compounds in raw water samples, evaluated their removal during coagulation, ozonation, biofiltration, and disinfection, and assessed their adsorption onto powdered activated carbon. Legacy PFASs frequently exceeded the EPA lifetime health advisory, while PFECAs were largely absent from raw water but, when present, showed high concentrations and poor removal by conventional treatment, and adsorption onto powdered activated carbon increased with chain length but was reduced by ether oxygen substitutions.

Abstract

Long-chain per- and polyfluoroalkyl substances (PFASs) are being replaced by short-chain PFASs and fluorinated alternatives. For ten legacy PFASs and seven recently discovered perfluoroalkyl ether carboxylic acids (PFECAs), we report (1) their occurrence in the Cape Fear River (CFR) watershed, (2) their fate in water treatment processes, and (3) their adsorbability on powdered activated carbon (PAC). In the headwater region of the CFR basin, PFECAs were not detected in raw water of a drinking water treatment plant (DWTP), but concentrations of legacy PFASs were high. The U.S. Environmental Protection Agency's lifetime health advisory level (70 ng/L) for perfluorooctanesulfonic acid and perfluorooctanoic acid (PFOA) was exceeded on 57 of 127 sampling days. In raw water of a DWTP downstream of a PFAS manufacturer, the mean concentration of perfluoro-2-propoxypropanoic acid (PFPrOPrA), a replacement for PFOA, was 631 ng/L (n = 37). Six other PFECAs were detected, with three exhibiting chromatographic peak areas up to 15 times that of PFPrOPrA. At this DWTP, PFECA removal by coagulation, ozonation, biofiltration, and disinfection was negligible. The adsorbability of PFASs on PAC increased with increasing chain length. Replacing one CF2 group with an ether oxygen decreased the affinity of PFASs for PAC, while replacing additional CF2 groups did not lead to further affinity changes.