Per- and Polyfluoroalkyl Substances in Southern Ontario Drinking Water and Wastewater

The presence of 41 per- and polyfluorinated alkyl substances (PFAS) was investigated in raw and finished drinking water and in influent and effluent wastewater sampled from facilities in the Great Lakes Basin region of Southern Ontario, Canada (September–November 2023). Based on US Environmental Protection Agency Method 1633A, the method developed for analysis of these species demonstrates high sensitivity and recovery with limits of quantitation that range between 0.075 ng L–1 and 3.0 ng L–1. Linear chain PFAS with carboxylic acid and sulfonic acid groups were detected in finished water from all drinking water treatment plants (n = 6). Wastewater effluents (n = 2) had PFAS concentrations approximately 1 order of magnitude higher than those in finished drinking water samples and included several fluorotelomers and ether-linked species. Across all sites, 13 of the 41 PFAS were detected in drinking water and 21 in wastewater. Average sum of 25 PFAS in finished drinking water ranged between 8.69 and 14.0 ng L–1, well below Health Canada’s objective of 30 ng L–1. These results highlight the persistence of PFAS across treatment systems and suggest a potential feedback loop where wastewater effluents reintroduce PFAS into surface waters used as drinking water sources.