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.