California’s surface water and sediment are often contaminated with PFAS pesticides

Pesticides that are part of the family of toxic “forever chemicals” known as PFAS contaminate surface water and sediment in agricultural areas across California, an EWG analysis finds.

PFAS pesticides were found in up to 50% of California surface water samples, and in about 45% to 55% of sediment samples. These chemicals – fungicides, herbicides and insecticides – do not just end up on produce that feeds the nation. These findings suggest pesticides could also be exposing millions of Californians to PFAS through water and soil. 

What’s worse, exposure may persist for generations, since PFAS never fully break down in the environment. 

To reduce water and soil contamination from PFAS pesticides, California should phase out their use, sale and manufacture for agricultural uses.

Potential health concerns

PFAS pesticides are those whose active ingredients meet the internationally recognized definition of per- and polyfluoroalkyl substances. These active ingredients have the carbon-fluorine bond characteristic of PFAS chemicals, which makes them highly persistent in the environment and resistant to complete breakdown.

EWG recently revealed over 2.5 million pounds of PFAS pesticides are applied on California farmland annually, and also found frequent detections of these chemicals on produce grown in the state.

Exposure to PFAS pesticides could harm the immune system. Yet EWG’s published research highlighted an important oversight gap: Review of studies of immune system toxicity – a key outcome observed in several studies of PFAS exposure – is routinely waived as part of PFAS pesticide approvals.

Many PFAS pesticides also transform in the environment into a highly persistent, short-chain form called trifluoroacetic acid, or TFA. Early research has linked TFA exposure with reproductive and developmental risks. There are also concerns about TFA’s ability to persist in the environment for an extremely long time.

We don’t know how long it takes for PFAS pesticides to degrade into TFA. It varies according to pesticide types and environmental conditions. 

In the absence of comprehensive monitoring for TFA and PFAS pesticide breakdown products, current exposure estimates don’t fully account for the range of how these chemicals can harm our environment and health.

EWG’s new analysis is a significant step forward in trying to capture the many ways we are exposed to PFAS.

Studying surface water

Our analysis of sampling results found multiple PFAS pesticides were detected in California surface water. 

To quantify the extent of PFAS pesticide contamination of California surface waters near agricultural areas, EWG compared four subsets of data. The number of PFAS pesticide samples for each dataset is denoted by n in the list below.

1. 2025 Surface Water Database, or SURF (n = 4,158): Surface Water Monitoring Studies 304, 301 and 321 with results spanning 2020-2023, from the California DPR, obtained from the 2025 DPR SURF Release:

Counties sampled: Butte, Colusa, Imperial, Merced, Monterey, San Luis Obispo, Santa Barbara, Stanislaus, Sutter, Yolo.

Waterbody/watershed sampled: Alamo River, Butte Creek, Clarks Ditch-Colusa Basin Drain, Ingram Creek, Lower Logan Creek, New River, Salinas River, Santa Maria River, South Slough-Deadman Creek, Tembladero Slough, Town of Hilmar-San Joaquin River, Willow Creek.

2. 2026 Study 310 (n = 298): Summary data from DPR Study 310, published in a January 7, 2026, report, with pesticide monitoring data on near-agricultural areas for Northern California in 2024:

Counties sampled: Butte, Colusa, Merced, Stanislaus, Sutter, Yolo 

Waterbody/watershed sampled: Butte Creek, Clarks Ditch-Colusa Basin Drain, Ingram Creek, Lower Logan Creek, South Slough-Deadman Creek, Town of Hilmar-San Joaquin River, Willow Creek

3. 2026 Study 321 (n = 548): Summary data from DPR Study 321, published in a January 1, 2026, report, with pesticide monitoring data on near-agricultural areas for the Central Coast and Southern California in 2024:

Counties sampled: Imperial, Monterey, San Luis Obispo, Santa Barbara 

Waterbody/watershed sampled: Alamo River, New River, Oso Flaco Creek, Salinas River, Santa Maria River, Tembladero Slough

4. USGS (n = 580): Data from Table S4 of Woodward et al. (2026), with 2024 pesticide sampling data collected from agricultural streams in California, conducted by the USGS:

Counties sampled: Butte, Merced, San Joaquin, Solano, Stanislaus, Sutter, Yolo

Waterbody/watershed sampled: Butte Creek, Colusa Basin Drainage Canal, Del Puerto Creek, French Camp Slough, Ingram Creek, Mustang Creek, Orestimba Creek, Reclamation Drain, Snake River, Sweeney Creek

Because the data underlying Study 310 and Study 321 for samples collected in 2024 were not available within the SURF database as of the publication of this article, EWG’s analysis utilized summary statistics from DPR within the preliminary reports published in early 2026.

Information on PFAS pesticide detection frequencies from these data sources is summarized in Table 1, below. Data for the 10 most frequently detected PFAS pesticides between 2020 and 2023 in California SURF data are shown.

Table 1. Multiple PFAS pesticides detected in California surface water. 

^{Gray cells indicate no testing for corresponding PFAS pesticide. ND = not detected.}

Detection frequencies differed by region and study design. For example, oxyfluorfen detections varied by 21% across the data. But all four studies in Table 1 found evidence of PFAS pesticide contamination of surface water near agricultural areas.

Similar detection frequencies for bifenthrin – about one in three samples – were observed in both study regions, showing widespread bifenthrin contamination of state surface waters.

Data for the PFAS pesticides oxyfluorfen and lambda-cyhalothrin also showed frequent detections in state agricultural waterways both in SURF data (range: 12.1% to 41%) and within the 2024 results in Study 321 (range: 20.4% to 36.8%). 

Some county-level patterns in PFAS pesticide detections were observed from SURF data. Between 2020 and 2023, pesticide monitoring of near-agricultural surface water showed higher overall detection frequencies in San Luis Obispo (mean detection frequency = 23%) and Monterey (22%) counties than the other eight counties covered. 

Bifenthrin was detected in all 15 samples from San Luis Obispo, and in 88% of samples from Stanislaus County. In Butte and Colusa counties, all 10 PFAS pesticides shown in Table 1 were detected in under 10% of samples. 

The number of PFAS pesticides detected in surface water by county varied, with 10 detected in Monterey County, compared to just one in each of Sutter and Merced counties.

Notably, data for Fresno and Kern counties, where PFAS pesticide applications are the highest in the state, were not reported in the agricultural surface water or sediment monitoring studies within SURF. This suggests a concerning gap in the state of California’s testing of PFAS in surface water. 

Assessing sediment

EWG’s analysis found that both PFAS pesticides that were tested for in California sediment were frequently detected.

SURF data were subsetted to the same three datasets on pesticide monitoring in agricultural areas, and summary data were extracted from the 2026 Study 310 and Study 321 reports. The USGS dataset did not report concentrations for sediment and was not included.

Altogether, sediment data were far sparser than surface water data, with a much smaller set of pesticides sampled. 

In the 2020-2023 subset of SURF data and in the 2026 Study 310 data, only seven pesticides were sampled in total, while eight were sampled in the 2026 Study 321 data. 

Across all three datasets, just two of the sampled chemicals – bifenthrin and lambda-cyhalothrin – were PFAS pesticides. 

Table 2. Bifenthrin and lambda-cyhalothrin were frequently detected in California sediment.* 

^{Number of PFAS pesticide samples denoted by n.}

*Due to a testing error in the 2026 Study 321 results, no sediment data were available from the Imperial Valley, a major agricultural region in southeastern California. The report notes this lack of data "significantly impacted 2024 results" and resulted in a drop in the detection frequency for lambda-cyhalothrin in sediment, from 80% in 2023 to 30% in 2024.

Between 2020 and 2023, SURF data indicated both bifenthrin and lambda-cyhalothrin were more frequently detected than the other five non-PFAS pesticides.

The sediment analysis is far more limited due to smaller sample sizes, limited pesticide coverage and testing errors (see Table 2 footnote). 

Only two PFAS pesticides were tested for, despite several more being applied to crops, detected on produce and frequently found in nearby surface waters. 

These data gaps almost certainly lead to underestimated PFAS contamination in sediment. With more frequent and geographically diverse sampling, as well as consideration of a wider variety of chemicals, detections would likely rise. These limitations also hinder geographic comparisons of sediment.

Nevertheless, the findings in Table 2 indicate that, at minimum, bifenthrin and lambda-cyhalothrin have both contaminated sediment in areas near agricultural land in California. 

Need for more comprehensive monitoring

Our analysis looked at surface water and sediment test results from the California Department of Pesticide Regulation, or DPR, and the U.S. Geological Survey.

Bifenthrin, a PFAS pesticide that may be linked to cancer, was detected in almost half of all surface water samples and in over half of the sediment samples between 2020 and 2023.

Overall sampling data are limited in size and scope, so PFAS contamination from pesticide use is likely more widespread than the data currently suggest. This report emphasizes the need for much more extensive environmental monitoring. 

Current test panels don’t sample for all PFAS pesticides or the chemical breakdown products that can form in the environment, so the full picture of contamination remains unclear. But EWG’s findings, based on current data only, highlight ample reason for concern.

Addressing PFAS pesticides

To eliminate the concerns over PFAS pesticides and their presence on produce, sediment and surface water, California should move to phase out the use of these chemicals on crops. Ending the use of PFAS pesticides would safeguard our food and water systems and prevent PFAS pesticide buildup in the environment.

Furthermore, current monitoring of both surface water and sediment looks at individual pesticides only, not the highly concerning PFAS byproducts that can form from their partial breakdown.