Farmworkers apply the fumigant 1,3-Dichloropropene to a field in Salinas, Calif.
Farmworkers apply the fumigant 1,3-Dichloropropene to a field in Salinas, California. Credit: Sam Hodgson for CIR

Dow AgroSciences has violated a California law by failing to warn a Central Valley community that it was exposed to risky levels of a cancer-causing pesticide, according to a new lawsuit by the Center for Environmental Health.

The suit alleges that the chemical company should have given notice to the residents of a community in Shafter, California, when growers used 1,3-Dichloropropene, a popular but toxic pesticide manufactured exclusively by Dow.

Although warning signs are routinely posted at the edge of the fields after 1,3-D is applied, the lawsuit claims that Dow should directly notify residents when the chemical is being used nearby.

“Despite the fact that Defendants expose pregnant women, children and other individuals to 1,3-D, Defendants provide no warnings whatsoever about the carcinogenic hazards associated with 1,3-D exposure,” the lawsuit says.

The Center for Environmental Health brought the case under a law commonly known as Proposition 65, which requires the state to maintain a list of chemicals that cause cancer, birth defects and reproductive problems. The law also says that businesses must notify the public when a significant amount of a Prop. 65 chemical is released into the environment.

Under Prop. 65, the term “significant amount” has a specific definition: For carcinogens, it’s a level where someone who comes into contact with the chemical over 70 years – which is considered a lifetime of exposure – would have more than a 1-in-100,000 chance of getting cancer.

That’s the central issue that this case will turn on: Were Shafter residents put at extra cancer risk and then not warned about it?

Normally, that’s a hard thing to prove, especially when it comes to pesticides. It is extremely difficult to prove causation between toxins like 1,3-D and specific cases of cancer, and the lawsuit does not claim that any specific Shafter residents have been made ill by the pesticide.

But it turns out that Shafter, the city at the heart of this lawsuit, is one of six places where the state of California has placed monitors to track pesticides in the air. The idea behind the monitors is to make sure that the state’s regulations are working.

In the past four years, the monitor in Shafter has picked up levels of 1,3-D that, when averaged together, have gone beyond what the California Department of Pesticide Regulation believes will keep residents under that 1-in-100,000 chance of getting cancer.

The department’s most recent air monitoring report says that if things continue this way, the cancer risk for residents would be nearly two times higher than the state’s public health target.

Caroline Cox, research director at Oakland-based Center for Environmental Health, said that according to her read of the state’s air monitoring results, Dow should have done more to warn residents about 1,3-D in Shafter, as Prop. 65 requires.

“You have to provide warnings before there is significant exposure of a toxic chemical and measuring the exposure for pesticides is complicated,” Cox said. “But here is one case where we have the state collecting data about exposure and that data is showing that it’s too much.”

The Department of Pesticide Regulation declined to comment on the lawsuit.

David Sousa, a manager at Dow AgroSciences, said in a written statement that additional warnings were not necessary and the suit has no merit. “The science is clear that 1,3-D does not present a health risk at levels of potential exposure associated with normal product use in accordance with all legal requirements,” he wrote.

By definition, exposure to toxic chemicals does in fact carry a health risk. In the case of 1,3-D, it’s a poisonous gas that’s injected into the soil before a crop is planted as a way to clear the earth of disease or pests. Popular with strawberry and sweet potato growers, the fumigant is invisible, and evaporates easily. If it escapes from the ground, it can linger near houses, schools and businesses, where people can inhale it.

And the state has a history of allowing growers to use 1,3-D at levels that its own scientists don’t believe are sound.

After alarming levels of 1,3-D were detected in the air in 1990, the California Department of Pesticide Regulation pulled it from use. The state then created a special regulatory system to limit how much 1,3-D could be used in a year in each community. Nevertheless, at the behest of Dow, state regulators agreed to create a loophole that allowed the pesticide to be used in some places at twice or three times the limit in some years, as our previous investigation showed.

This loophole was challenged by the state’s own scientists, but they were ignored. As a result, for more than a decade, over 100 California communities were put at higher risk for cancer than the state thought was acceptable.

Notably, the community in Shafter was not one where excessive 1,3-D was used. It also is not among the places in California where 1,3-D use is the highest.

Cox of the Center for Environmental Health said that this shows that there are other California communities – like those where growers took advantage of the 1,3-D loophole or other communities in Shafter close to farm fields – that potentially also warrant Prop. 65 warnings. The issue, she said, is that “we just don’t have the air monitoring data to back it up.”

Bernice Yeung can be reached at Follow her on Twitter: @bmyeung.

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Bernice Yeung is a reporter for Reveal, covering race and gender. Her work examines issues related to violence against women, labor and employment, immigration, and environmental health. Yeung was part of the national Emmy-nominated Rape in the Fields reporting team, which investigated the sexual assault of immigrant farmworkers. The project won an Alfred I. duPont-Columbia University Award and a Robert F. Kennedy Journalism Award and was a finalist for the Goldsmith Prize for Investigative Reporting. Yeung also was the lead reporter for the national Emmy-nominated Rape on the Night Shift team, which examined sexual violence against female janitors. That work won an Investigative Reporters and Editors Award, the Society of Professional Journalists Sigma Delta Chi Award for investigative journalism, and the Third Coast/Richard H. Driehaus Foundation Competition. Those projects led to ​​her first book in 2018, “In a Day's Work: The Fight to End Sexual Violence Against America's Most Vulnerable Workers.”  

A former staff writer for SF Weekly and editor at California Lawyer magazine, Yeung has had her work appear in a variety of media outlets, including The New York Times, The Seattle Times, The Guardian and PBS FRONTLINE. She has a bachelor's degree in journalism from Northwestern University and a master's degree from Fordham University, where she studied sociology with a focus on crime and justice. She was a 2015-16 Knight-Wallace fellow at the University of Michigan, where she explored ways journalists can use social science survey methods in their reporting. Yeung is based in Reveal's Emeryville, California, office.