You Can't See It, But You're Breathing It: Pesticide Exposure in California's Farm Communities
Despite it's reputation for being a leader in environmental policy, California faces ongoing concern over pesticide exposure to food systems, workers and communities. While studies show that people living near farmland face elevated pesticide exposure, comprehensive data on what they're personally breathing remains scarce.
In 2021, researchers at the University of California, Davis worked with Californians for Pesticide Reform and community members in the San Joaquin Valley on a project to measure a wide range of pesticides using personal air samples. The California Air Resources Board’s Community Air Grants program funded the project.
Pesticides target and are toxic to certain organisms and are associated with a number of adverse human health effects. When farmers spray pesticides on fields, there is drift on the day of the application, as well as on the days that follow through volatilization and other processes such as wind erosion, soil particle movement and particles from the wind.
In the UC Davis study, researchers recruited adult and school-aged participants from small agricultural towns in the San Joaquin Valley. There were 31 adult and 11 school aged participants with sampling occurring over 92 days.
Pesticide Exposure Study Results: What Researchers Found in the Air Samples
Participants wore a backpack sampler for 8 to 14 hours on 1-3 days. Samples were collected on two tubes, one with Tenax-TA resin and the other with XAD-2 resin. 21 pesticides were analyzed in total, using both LC/MS and GC/MS methods.
The results revealed detectable levels of pesticides in a significant proportion of participants’ samplers. Specifically, 22% of adults and one school-aged child had measurable levels of at least one pesticide in their samplers, including compounds such as 1,3-dichloropropene, chlorpyrifos (despite its banned status in California), pyrimethanil, buprofezin, and penthiopyra.
- 1,3-dichloropropene, listed as a carcinogen in California under Proposition 65 and classified as a likely human carcinogen by the US EPA. There are active efforts to reduce use in California.
Chlorpyrifos is clearly demonstrated to have a number of adverse health effects, and as a result, tolerance levels on food products have been revoked nationwide. It was banned for use in California in 2021, with the exception of granular formulations. The most recent EPA risk assessments considers both AChE inhibition and potential for neurodevelopmental effects as the primary endpoints of concern.
While the toxicity of the other compounds has been less studied, there is the potential for adverse health impacts.
- Developmental toxicity has been observed in both rats and mice for the fungicide pyrimethanil. Also of concern is the potential for endocrine disruption. A study in zebrafish found altered expression of genes related to the endocrine system, as well as oxidative stress.
- Buprofezin, an insecticide that acts on immature insect developmental stages has been found to cause malformations in embryos of catfish larvae. The compound has also been tested in mice and human cell lines.
- Penthiopyrad, a fungicide and the least studied of the detected compounds, warrants further investigation due to preliminary findings of developmental and metabolic disruptions in zebrafish models.
With the new notification regulation, we will have the opportunity to measure personal exposure when we know pesticides are being applied. It’s critical to take the guesswork out of monitoring and to measure real exposure. Jane Sellen, Californians for Pesticide Reform
Deborah Bennett, Ph.D., Professor of Public Health Sciences at the University of California, Davis, emphasizes the urgency to expand the scope of pesticide monitoring efforts. "Our findings underscore the need for broader surveillance of pesticide exposure. Current measures are insufficient to capture exposure to several compounds with documented toxicological risks," says Dr. Bennett.
"This study underscores the prevalence of pesticide exposure in agricultural communities," says Angel Garcia of Californians for Pesticide Reform. "It highlights the imperative for rigorous monitoring and regulatory action to safeguard public health."
The study highlights a critical gap: people are being exposed to pesticides that aren't routinely monitored, and the science suggests some of those compounds carry real health risks. A California pesticide notification system in development, expected to take effect in 2025, could be a turning point, giving scientists and communities the tools to measure exposure more precisely and act on what they find.
“We have reason to believe that the high level of exposure documented in this study is actually an under-count,” said Jane Sellen of Californians for Pesticide Reform and the community PI on the study. “For too long, applications of hazardous chemical pesticides have been a closely guarded secret. With the new notification regulation, we will have the opportunity to measure personal exposure when we know pesticides are being applied. It’s critical to take the guesswork out of monitoring and to measure real exposure.”