Perfluoroalkyl Acids in Great Lakes Precipitation and Surface Water (2006-2018) Indicate Response to Phase-outs, Regulatory Action, and Variability in Fate and Transport Processes.

The concentrations of perfluoroalkyl acids (PFAAs) were determined in precipitation from three locations across the Great Lakes between 2006 and 2018 and compared to those in surface water. Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) concentrations generally decreased in precipitation, likely in response to phase-outs/regulatory actions. In comparison, concentrations of shorter-chained PFAA, which are not regulated in Canada did not decrease and those of perfluorohexanoate and perfluorobutanoate (PFBA) recently increased, which could be due to their use as replacements, as the longer-chained PFAAs are being phased-out by industry. PFOS and PFOA concentrations were greater in Lake Ontario precipitation than in precipitation from more remote locations. In comparison, PFBA concentrations were comparable across locations, suggesting greater atmospheric transport either through its more volatile precursors and/or directly in association with particles/aerosols. In Lake Ontario, the comparison of PFAAs in precipitation to those in surface water provides evidence of sources (e.g., street dust and wastewater effluent) in addition to wet deposition to surface water, whereas wet deposition appears to be dominant in Lakes Huron and Superior. Our results suggest that source control of shorter-chained PFAAs may be slow to be reflected in environmental concentrations due to emissions far from the location of detection and continued volatilization from existing in-use products and waste streams.