Assessing Pesticide Application Contributions of Per- and Polyfluoroalkyl Substances (PFAS) in Agricultural Streams

Research has documented per-and polyfluoroalkyl substances (PFAS) to be prevalent in streams impacted by urban sources; less is known regarding PFAS contributions via pesticide applications, potentially from pesticide containers and/or “inert” ingredients not listed on pesticide formulation labels. To assess co-occurrence of pesticides and PFAS in agricultural streams, 10 streams were sampled in two agricultural valleys in northern California, USA during two periods of pesticide application (May and July of 2024). Water samples were analyzed for 183 pesticides and 57 PFAS. Sixty pesticides were detected: 23 herbicides, 18 insecticides, 18 fungicides, and 1 insecticide synergist. Detection frequencies (DFs) ranged from 0 to 100%, and concentrations ranged from nondetect (ND) to 782 ng/L (fluxapyroxad). Fourteen PFAS were detected: 6 perfluoroalkyl carboxylates (PFCAs), 5 perfluoroalkyl sulfonates (PFSAs), 2 PFCA/PFSA precursors, and 1 perfluoroalkyl phosphinate with DFs ranging from 0 to 60% (perfluorooctonoate [PFOA]) and concentrations ranging from ND to 20 ng/L (perfluorobutanoate [PFBA]). Co-occurrences of PFAS and pesticides were observed in 80% of the samples. Adopting the Organisation for Economic Cooperation and Development PFAS definition, pesticide applications are a likely source of instream PFAS. Examination of total organic fluorine and transformations to terminal and ultrashort PFAS could further elucidate pesticide contributions to environmental PFAS.