Characterization of Per- and Polyfluoroalkyl Substances in Drinking Water Sources in the Greater Montreal Area, Quebec, Canada

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants that are subject to increasingly restrictive regulations. This study characterized the occurrence of 77 PFAS compounds in raw and treated water from 15 drinking water treatment plants (WTPs) in the Greater Montreal Area, including an urban creek receiving airport runoff. A total of 32 compounds were detected at least once, representing diverse classes and carbon chain lengths. This helped to identify trends and precursor impacts on the PFAS profiles. Perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl sulfonic acids (PFSA) were the most frequently detected. The highest concentrations occurred in WTPs drawing from the St. Lawrence River, while the Ottawa and L’Assomption Rivers demonstrated the occurrence of localized contamination. Conventional treatment showed negligible PFAS removal. WTPs drawn from the same water source were generally correlated. Correlation analyses also demonstrated that some plants are influenced by both the Ottawa and St. Lawrence Rivers. Airport-related PFAS compounds, such as those from aqueous firefighting foam and hydraulic fluids, were detected in downstream WTPs. Seasonal trends suggest that temperature and flow variations might affect PFAS concentrations. These findings illustrate the challenges when protecting water sources against PFAS at a basin scale while offering insights into how their patterns can assist with the identification of local contamination sources.

This study has shown that the existing conventional treatment processes are not efficient for PFAS removal. The highest PFAS concentrations were observed in the St. Lawrence River. While airport runoff, aqueous film-forming foams (AFFFs), and hydraulic fluids contribute to PFAS contamination, trends on PFAS classes and chain lengths related to sources and mixing of rivers were established.