Researchers found that pesticides classified as PFAS, often called “forever chemicals” because of their extreme persistence in the environment, were detected in as many as half of surface water samples collected near farmland across the state.

The findings reveal that contamination extends beyond crops and into rivers, streams and sediments that millions of Californians rely on.

PFAS pesticides were identified in approximately 45% to 55% of sediment samples and up to 50% of surface water samples collected from agricultural regions. The data suggest that exposure routes may include not only food but also contaminated soil and water.

As concerns grow over the long-term effects of PFAS chemicals, environmental advocates are urging California regulators to phase out PFAS pesticides used in agriculture.

Researchers warn that these substances can remain in ecosystems for generations, potentially creating lasting environmental and public health challenges.

What are PFAS pesticides?

PFAS pesticides contain active ingredients that meet the internationally recognised definition of per- and polyfluoroalkyl substances. These compounds contain strong carbon-fluorine bonds, making them exceptionally resistant to degradation.

The same chemical properties that make PFAS useful in industrial and agricultural applications also make them environmentally problematic. Once released, they can persist in soil, groundwater and surface water for years or even decades.

EWG recently reported that more than 2.5 million pounds of PFAS pesticides are applied annually on California farmland. Previous investigations also found traces of these chemicals on produce grown within the state.

Surface water testing reveals extensive contamination

EWG’s latest review analysed thousands of pesticide monitoring samples collected by the California Department of Pesticide Regulation (DPR) and the U.S. Geological Survey (USGS).

The assessment examined four major datasets covering agricultural waterways between 2020 and 2024. Sampling locations included rivers, drainage canals, creeks and sloughs across multiple farming regions in Northern California, the Central Coast and Southern California.

Despite differences in study design and geography, all four datasets found evidence of PFAS pesticide contamination in surface water near agricultural land.

One of the most frequently detected chemicals was bifenthrin, a PFAS pesticide that was detected in roughly one-third to one-half of water samples across the study areas.

Other commonly detected compounds included oxyfluorfen and lambda-cyhalothrin, both of which were repeatedly found in agricultural waterways.

Researchers noted that detection rates varied significantly by county. Monterey and San Luis Obispo counties recorded some of the highest overall detection frequencies, while certain northern counties showed lower concentrations.

Sediment samples show persistent chemical presence

The contamination was not limited to water.

Sediment testing conducted near agricultural areas also found PFAS pesticides at substantial rates. Between 45% and 55% of sediment samples contained PFAS compounds, primarily bifenthrin and lambda-cyhalothrin.

Scientists caution that sediment monitoring remains limited. Compared with surface water testing, far fewer sediment samples were collected, and only a small number of pesticides were included in testing programmes.

As a result, experts believe current figures may significantly underestimate the true extent of contamination.

Because sediment can act as a long-term reservoir for pollutants, contamination in riverbeds and stream sediments may continue affecting ecosystems long after pesticides are applied.

Concerns over toxic byproducts

Environmental scientists are increasingly concerned not only about PFAS pesticides themselves but also about what happens when they break down.

Many PFAS pesticides eventually transform into trifluoroacetic acid (TFA), an extremely persistent short-chain PFAS compound. Emerging research has linked TFA exposure to potential reproductive and developmental effects, although scientists continue to investigate its full health impacts.

A major challenge is that researchers still do not know exactly how quickly different PFAS pesticides degrade into TFA. Environmental conditions, soil characteristics and pesticide formulations can all influence the process.

Current monitoring programmes rarely test for TFA or other PFAS breakdown products, leaving significant gaps in understanding the full scope of environmental exposure.

Potential health risks under scrutiny

Growing evidence suggests PFAS pesticides may pose risks to human health beyond direct environmental contamination.

Studies have linked PFAS exposure to immune system disruption, and researchers have raised concerns that existing pesticide approval processes may not adequately evaluate these effects.

According to EWG, reviews of immune-related toxicity have frequently been waived during assessments of PFAS pesticide products, potentially leaving regulators with incomplete information about long-term health impacts.

The issue has attracted increasing attention as scientists continue to uncover new evidence connecting PFAS exposure to a range of health concerns.

Major monitoring gaps remain

Although the new analysis paints a concerning picture, researchers emphasise that existing data likely represent only part of the problem.

Several of California’s highest pesticide-use counties, including Fresno and Kern, were absent from the state’s agricultural surface water monitoring datasets reviewed by EWG.

These omissions raise questions about whether contamination levels in heavily farmed regions may be going undetected.

In addition, many PFAS pesticides currently used in agriculture are not routinely included in monitoring programs. Testing generally focuses on individual pesticides rather than the broader family of PFAS compounds and their degradation products.

Experts argue that more comprehensive environmental surveillance is needed to assess risks to ecosystems and nearby communities accurately.

Calls for a phase-out of PFAS pesticides

In response to the findings, EWG is calling for California to phase out the agricultural use, sale and manufacture of PFAS pesticides.

Supporters of stricter regulation argue that eliminating these chemicals would help prevent future contamination of food supplies, waterways and agricultural soils.

They also contend that proactive action is necessary because PFAS compounds accumulate over time and remain in the environment long after their initial application.

With contamination already detected across multiple regions and environmental media, advocates say California has an opportunity to lead efforts to reduce PFAS pollution at its source.

The bottom line

The latest analysis suggests PFAS pesticides are contaminating California’s agricultural waterways at levels that warrant closer scrutiny.

Evidence of widespread detection in both surface water and sediment, combined with concerns over persistent byproducts such as TFA, highlights a growing environmental challenge.

While significant data gaps remain, researchers say the findings underscore the need for expanded monitoring, stronger regulatory oversight and a long-term strategy to reduce reliance on PFAS pesticides before contamination becomes even more entrenched in California’s environment.