An analysis of state and federal records indicates that approximately half of California waterways tested by regulators are contaminated with pesticides classified as per- and polyfluoroalkyl substances, commonly known as “forever chemicals.” The review, released this week, marks the first systematic assessment of the substances in streams and rivers that serve as drinking water sources.
The analysis combined data from the California Department of Pesticide Regulation and the United States Geological Survey. In addition to water contamination, more than half of the sediment samples collected across the tested regions showed detectable levels of the chemical residues.
Pfas encompass a class of at least 16,000 compounds designed to be water-, stain- and grease-resistant. They have been linked to severe health problems, including cancer, birth defects, decreased immunity, high cholesterol and kidney disease. The chemicals are applied to food crops either as active ingredients to kill weeds and insects, or as inert ingredients. A 2023 analysis of Environmental Protection Agency data found that at least 60 percent of pesticide active ingredients fit the widely accepted definition of Pfas.
“It’s concerning that we’re finding these levels of Pfas pesticide,” said Varun Subramaniam, a co-author of the report with the Environmental Working Group. “But they were applied at really high rates on produce, so it makes sense that they’re in the streams and sediment.”
State records reviewed last year showed that California farms applied an average of 2.5 million pounds of Pfas per year on cropland from 2018 to 2023. Recent regulatory testing found pesticide residues on 37 percent of all produce. The contamination is highly concentrated on specific crops: about 90 percent of peaches, plums and nectarines contained Pfas, while 80 percent of strawberries and grapes tested positive.
Regulators collected water samples from only 10 counties, finding the highest concentrations in agricultural zones such as Monterey and San Luis Obispo counties. Previous research indicated that Fresno and Kern counties saw the heaviest application of Pfas pesticides, but water pollution data was not gathered there. Subramaniam noted that the findings are “almost certainly an undercount” because of the limited geographic scope. At least 10 distinct Pfas compounds in pesticides were identified across the state. The highly toxic pesticide bifenthrin, which is linked to cancer, appeared in all San Luis Obispo waterways and more than 80 percent of samples in Stanislaus County.
Health risk assessments are complicated by gaps in pesticide testing requirements. Subramaniam stated that companies are not required to evaluate many health threats common to Pfas, such as immunotoxicity, reproductive harm or hormone disruption, partly due to a lack of regulatory resources. Regulators also do not currently evaluate the cumulative health effects of consuming both drinking water contaminated with Pfas and produce treated with the residues.
“The fact that the chemicals are permitted is largely because we’re not considering all the ways that they can harm us,” Subramaniam said.
Amid intense pressure from agricultural lobbying groups, a proposal to ban Pfas pesticides entirely by 2035 failed to pass the California State Assembly. The bill’s opponents, including the California Farm Bureau, argued that the measure was an “overly broad and unworkable approach that departs from science-based regulation.” The bureau warned that the ban would place farmers at an economic disadvantage with little public health benefit.
Despite the stalled ban, pieces of the legislation succeeded. A moratorium on approving new Pfas pesticides survived, along with a requirement that pesticides carry warnings alerting farmers to the health and environmental risks of the chemicals. Susan Little, the California legislative director for the Environmental Working Group, said most farmers are unaware they are applying Pfas to food crops. The bill also empowers local leaders to restrict pesticide use and aligns the state’s definition of Pfas with broader scientific standards, moving away from the California pesticide office’s narrow industry-preferred definition.
Advocates emphasized the urgency of state action given the Trump administration’s pace in approving additional Pfas pesticides for use. They also pointed to the California pesticide office’s recent reapproval of sulfoxaflor, a Pfas insecticide whose authorization has been repeatedly struck down by courts for its high toxicity to honeybees and other pollinators.
“We are disappointed” the full ban did not survive, Little said, but noted the legislation, if approved by the state senate, “will continue to address and reduce the use of Pfas pesticides in California.”