A sweeping analysis of California's water systems has detected dangerous pesticides known as Pfas in roughly half of the state's tested streams and rivers, many of which feed drinking water supplies. The findings mark the first systematic statewide survey of these persistent contaminants in waterways and underscore how widely the chemicals have infiltrated the environment through agricultural use.
Pfas, shorthand for per- and polyfluoroalkyl substances, are dubbed "forever chemicals" because they break down extremely slowly, persisting for millennia in soil and water. At least 16,000 compounds fall into this class, which manufacturers have designed to resist water, stains, and grease. California farms have sprayed an average of 2.5 million pounds of Pfas-containing pesticides annually between 2018 and 2023, according to state records.
The contaminants have been linked to cancer, kidney disease, birth defects, weakened immunity, and high cholesterol. Yet regulators have approved their continued use in agriculture, in part because pesticide law does not require comprehensive health assessments of Pfas effects like reproductive harm or hormone disruption.
Sediment samples from the tested waterways also revealed contamination, with more than half showing detectable pesticide residues. The analysis examined data from the California Department of Pesticide Regulation and the United States Geological Survey, focusing on 10 counties. Researchers found the highest concentrations in agricultural regions, particularly Monterey and San Luis Obispo counties.
Bifenthrin, one of the most toxic Pfas pesticides and linked to cancer, turned up in every waterway tested in San Luis Obispo County and in more than 80 percent of samples from Stanislaus County, which includes parts of the Central Valley and the city of Modesto.
The contamination mirrors pesticide application patterns. Recent regulatory testing revealed that 37 percent of all produce carries Pfas residues, but the contamination is far heavier on specific crops. About 90 percent of peaches, plums, and nectarines tested positive, as did 80 percent of strawberries and grapes.
Varun Subramaniam, co-author of the analysis with the Environmental Working Group, called the results "alarming but not surprising" given the intensity of pesticide application. He noted that the findings likely undercount the true extent of contamination because testing covered only 10 counties and excluded areas like Fresno and Kern, which have the highest recorded Pfas pesticide applications.
The discovery arrives as California's legislature grapples with how to regulate these chemicals. A proposal to fully ban Pfas pesticides by 2035 failed to clear the state assembly this week, but a moratorium on approving new Pfas pesticides advanced. The final bill also requires pesticide manufacturers to label products as containing Pfas and gives local governments authority to restrict their use.
The legislation redefines Pfas using a broader, science-based definition rather than the narrow interpretation California's pesticide office currently employs, one favored by industry because it excludes smaller compounds used in pesticides.
The California Farm Bureau opposed the full ban, arguing it represents an "overly broad and unworkable approach" that would disadvantage state farmers with minimal public health benefit. The powerful agricultural lobby's resistance proved decisive in blocking the more stringent measure.
Subramaniam emphasized that regulators have failed to account for cumulative Pfas exposure from both drinking water and contaminated food. "The fact that the chemicals are permitted is largely because we're not considering all the ways that they can harm us," he said.
Susan Little, California legislative director for the Environmental Working Group, expressed disappointment that the full ban did not survive, though she noted that the partial restrictions would still curtail Pfas pesticide use if the state senate approves them.
The timing of California's legislative fight comes as the Trump administration has moved to approve additional Pfas pesticides. California's pesticide office also recently reapproved sulfoxaflor, a Pfas insecticide, despite repeated court decisions striking down its approval over toxicity concerns for honeybees and other pollinators.
Author James Rodriguez: "California's half-measures on forever chemicals feel like rearranging deck chairs while the ship fills with contaminated water."
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