California regulators passed a rule in January 2024 that they say will protect communities from one of the state’s most popular and dangerous pesticides.
1,3-dichloropropane (1,3-D) has been known for decades to cause tumors in multiple organs in laboratory animals, so much so that the state flagged it as a carcinogen in 1989. But before planting strawberries, almonds, grapes and other multibillion-dollar crops, regulators were allowing growers to fumigate fields with large doses of 1,3-D to kill anything living in the soil.
But a year after regulators implemented a rule that says it reduces the amount of 1,3-D in the air, thereby reducing the risk of cancer, state records show that applications of the highly volatile compound have skyrocketed.
Growers applied 1 million more pounds of 1,3-D last year than in 2023, before regulators enacted the “residential bystander” rule, and in 2024, after the rule went into effect.
The highest increases were in Kern and San Joaquin counties, which were primarily used for almond and grape plantings. Notably, the “adjusted total pounds,” which takes into account different application methods, weather conditions, and other factors that affect how much volatile pesticide leaks into the air, nearly doubled in both counties and increased by nearly 20 percent statewide.
“Their new regulations are a failure,” said Mark Weller, campaign director for Californians for Pesticide Reform, a statewide coalition of public interest groups. “They introduced new regulations and the use of 1,3-D increased.”
In 2024, the Department of Pesticide Regulation (DPR) enacted new rules restricting the use of 1,3-D to protect residential bystanders by implementing setback distances, requiring deeper injection into soils with high moisture content, and establishing new fumigation methods and tarpaulin requirements to reduce fumigant emissions into the atmosphere, said department spokeswoman Amy McPherson. “DPR has specifically developed a method that allows for comparable levels of usage while reducing overall emissions.”
Ann Cutten, director of the Pesticides and Occupational Safety and Health Project at the nonprofit California Local Law Assistance Foundation, analyzed the emissions detected by the air monitor in Derry, California, one of six monitors operated by DPR. Katten found that in the first three quarters of 2025 (the most recent publicly available data), average levels of 1,3-D in the air increased by 30% compared to the same period in 2024.
Derry is a predominantly Latino town in Merced County, where a $10 billion agriculture industry employs one in five residents, and where farmers primarily use 1,3-D to grow almonds and sweet potatoes. Merced is also where regulators found alarmingly high levels of 1,3-D at the middle school in 1990 and suspended its use for five years.
Public health policy assumes that there is no safe level of exposure to carcinogens, taking into account differences in exposure and variation in susceptibility among different populations. Fumigants like 1,3-D can also cause serious short-term symptoms such as difficulty breathing, chest pain, eye irritation, and dizziness.
A warning sign is posted at the edge of a celery farm in California’s Salinas Valley shortly after pesticide application, indicating that it is dangerous to enter the field. Credit: Jack Clark/Universal Images Group via Getty Images
In 2023, Chinese researchers reported what appears to be the first fatal case of inhalation of 1.3-D. 1.3-D typically causes nausea, dizziness, and headaches in exposed California farm workers. A 50-year-old Chinese greenhouse worker died of kidney failure and brain swelling more than a week later after a brief encounter with 1,3-D in a poorly ventilated workplace.
According to Pesticide Action Network International, 1,3-D is currently banned in 40 countries.
Caroline Cox, a retired agrochemical scientist and former research director at the nonprofit Center for Environmental Health, said the point of the regulations was not necessarily to reduce the use of 1,3-D, but to reduce emissions. “I don’t think the regulations are really working as intended.”
The farmworker community and its allies have attempted lawsuits, media campaigns, and persistent protests to force pesticide regulators to protect them from 1,3-D. In February, they went to court again seeking relief for DPR’s “continued failure to meet its legal obligations to protect farm workers and other members of the public from toxic and carcinogenic fumigants.”
DPR currently has two different safety levels for the same chemical: the 2024 Residential Bystander Rule and a separate rule for professional bystanders that took effect in early 2026. Having two different 1,3-D regulatory targets for residents and workers does not take into account the fact that farmworker communities, where people live and work next to treated fields, typically face a much higher risk of exposure from childhood to old age.
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“Both regulations miss the mark and permit the continued use of 1,3-D in a manner that does not meet DPR’s legal obligations and does not adequately protect public health,” farm worker and community advocates argued in a legal brief.
Before enacting the new rules, DPR capped the amount of 1,3-D growers that could apply within an approximately 36-square-mile area called a township. DPR did not include a township cap in the 2024 regulations because the agency anticipated that setbacks and other additional requirements could reduce both acute and cancer risks. Still, a court order left the cap in place until January, when the professional bystander rule went into effect.
One township in Kern County has already exceeded the previously mandated annual township limit, and several townships in Kern and Merced counties are approaching that limit in the first quarter of this year alone, according to state records. As a 2024 Inside Climate News analysis found, a disproportionate burden of pesticide exposure falls on immigrants with limited English proficiency, who make up the majority of California’s farmworker population.
DPR’s McPherson attributes the increased application of 1,3-D to “an unusually high amount of replanting of vineyards and orchards in Kern County,” which occurs only about once every 10 to 20 years.
He said DPR is monitoring areas with relatively high usage in the first quarter, but needs to see a full year’s worth of data before drawing “any meaningful conclusions.”
DPR has announced plans to accelerate sustainable pest management in 2024, with a top priority goal of eliminating the negative impacts on human health and the environment associated with pesticide use. It does not include a list of priority pesticides.
Katten, of the California Rural Legal Assistance Foundation, is troubled by the increase in 1,3-D emissions after regulators remove the cap. “They were saying everything was going to be fine because things were trending down, but obviously that’s not the case,” Katten said. “Their sustainable pest management efforts have not yet borne fruit.”
In a recent meeting with DPR, Weller told staff members that the agency had previously worked to reduce the use of fumigants in California. “Are you still interested in it?” he asked.
No one said yes, he said.
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Lisa Gross is a reporter for Inside Climate News based in Northern California. She is the author of the Science Writer’s Handbook of Investigative Reporting and a contributor to the Science Writer’s Handbook. Both were funded by the National Science Writers Association’s Peggy Gershman Ideas Grant. She has covered science, conservation, agriculture, public and environmental health and justice for many years, with a focus on the misuse of science for private gain. Prior to joining ICN, he worked as a part-time journal editor for the open access journal PLOS Biology, a reporter for the Food & Environmental Reporting Network, and produced freelance articles for numerous national publications, including The New York Times, Washington Post, Discover, and Mother Jones. Her work has received awards from the Society of Healthcare Journalists, the American Society of Journalists and Authors, the Society of Professional Journalists NorCal, and the Society of Food Journalists.
