PFAS Pesticides Found in Half of California Surface Water and Sediment Tests, EWG Reports

A new analysis from the Environmental Working Group (EWG), released in May 2026, found that PFAS pesticides contaminate roughly half of California’s surface water and sediment, pointing to an under-recognized pathway for forever chemicals to reach the environment — and potentially drinking-water sources. The headline compound, bifenthrin, a widely used insecticide that EWG classifies as a PFAS and that has been potentially linked to cancer, turned up in nearly half of surface-water samples and more than half of sediment samples statewide.

The finding reframes a chemical class usually associated with industrial sites, firefighting foam, and consumer products. It arrives the same month the EPA moved to rescind four federal PFAS drinking-water standards — and it suggests the PFAS problem is broader, and more agricultural, than the regulatory debate has acknowledged.

What the Analysis Found

EWG examined surface-water and sediment monitoring data from the California Department of Pesticide Regulation and the U.S. Geological Survey, collected between 2020 and 2024 across ten counties, including Santa Barbara and Monterey. The pattern was consistent and regional:

Bifenthrin was detected in ~50% of surface-water samples and in over half of sediment samples.
Contamination was heaviest in agricultural regions — bifenthrin appeared in more than 80% of surface-water samples in San Luis Obispo and Stanislaus counties.
The chemical’s persistence is the concern: like other PFAS, it resists environmental breakdown and accumulates in sediment, where it can persist for years.

Why “PFAS Pesticide” Is the Key Phrase

Most public discussion of PFAS centers on compounds like PFOA and PFOS. But “PFAS” is a structural definition — any chemical containing carbon-fluorine bonds of a certain configuration — and a number of registered pesticides meet it. Bifenthrin is one of the most heavily used. That matters for three reasons:

Scale of application. Agricultural pesticides are applied across millions of acres, a far broader geographic footprint than point-source industrial PFAS.
Regulatory blind spot. PFAS drinking-water rules target a short list of named compounds; PFAS pesticides like bifenthrin generally aren’t on it, so systems aren’t required to monitor for them.
Pathway to drinking water. Surface water and sediment feed rivers and reservoirs that, in much of California, are drinking-water sources. Contamination in those waters is a plausible route to the tap that current monitoring largely misses.

EWG has tracked the broader scale of the problem — its mapping suggests PFAS reach roughly 176 million Americans’ tap water — and the California data adds an agricultural dimension to that picture.

The Data Has Big Gaps — and That Cuts One Way

EWG was explicit that its analysis likely undercounts the problem. The monitoring data excluded Fresno and Kern counties — the two counties that use the most PFAS pesticides in the state. Sampling overall was limited in size and scope. In other words, the half-of-samples figure comes from a dataset that omits the highest-use regions, so real-world contamination from PFAS pesticides is “likely more widespread than the data currently suggest,” in EWG’s framing.

The findings feed directly into a California legislative push to ban toxic PFAS pesticides, which advanced through Assembly appropriations panels this spring. WaterVerge has tracked how states are stepping in with their own PFAS actions as federal standards retreat.

What California Residents Should Do

For households on municipal water, this is primarily a source-water and policy story — but a few steps reduce exposure:

Know your source. Surface-water-supplied systems in agricultural regions face the most plausible exposure pathway; your annual Consumer Confidence Report identifies your source.
Filter for PFAS. Reverse osmosis and certified under-sink carbon and ion-exchange systems are the most effective residential options for PFAS broadly. Our PFAS explained guide details what each technology removes.
Private-well owners in farm country are most exposed and least protected — shallow wells near treated fields can pick up pesticide runoff. Review our private wells and PFAS guide and consider testing your well.
Pregnant residents and families with young children should prioritize filtration; see our pregnancy water quality guide.

What Comes Next

The EWG findings strengthen the case for California’s proposed PFAS-pesticide ban and for adding PFAS pesticides to routine surface-water and drinking-water monitoring. Whether regulators expand testing to cover Fresno, Kern, and other high-use counties will determine how complete the next picture is. For now, the data points to a category of PFAS contamination — agricultural, persistent, and largely unmonitored — that sits outside the federal drinking-water debate entirely.

How WaterVerge Tracks This

WaterVerge integrates EPA UCMR 5 PFAS monitoring and SDWIS data into our California and city pages. As California expands PFAS-pesticide monitoring and acts on its proposed ban, we’ll fold the resulting detections into the affected utilities’ records.