Concurrent Occurrence of Pesticides and Per- and Polyfluoroalkyl Substances (PFAS) in Agricultural Streams in California, USA

Per-and polyfluoroalkyl substances (PFAS) are frequently found in streams, with most research focusing on urban sources of PFAS to surface water (e.g., firefighting foams, industrial releases, and wastewater treatment plant discharges). Pesticide applications are an under-investigated source of PFAS to streams in both agricultural and urban areas. There are few studies that analyze the presence and concentration of pesticide compounds with respect to measurements of PFAS found in agricultural surface water canals. Although many PFAS are not applied as pesticides, there are concerns of increased PFAS levels in pesticide containers and as "inert" ingredients not listed on pesticide formulation labels. Additionally, some pesticide active ingredients can be considered PFAS. To better understand the potential co-occurrence of pesticides and PFAS in predominantly agricultural watersheds, 10 streams were sampled in northern California, USA in May and July of 2024 to coincide with peak target pesticide application timings. Water samples were analyzed for more than 183 pesticides and pesticide transformation products and 57 PFAS compounds.