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Researchers find pesticide spills, accidents may alter farmworkers’ DNA.
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Researchers find pesticide spills, accidents may alter farmworkers’ DNA.

Study of Iowa, North Carolina farmworkers finds high doses of pesticides can potentially impact DNA, triggering cancers later in life.

Farmworkers who have a high pesticide exposure event—such as a spill—are more likely to experience molecular changes on DNA that may lead to certain cancers, according to a large U.S. study of pesticide applicators in Iowa and North Carolina.


The research, part of the ongoing Agricultural Health Study that is monitoring the health of more than 57,000 private and commercial pesticide applicators in Iowa and North Carolina, adds to growing evidence that high exposure to certain pesticides may spur prostate and other cancers in people handling the chemicals.

“This lines up perfectly with what the National Cancer Institute is doing on the markers that increase the risk of cancer. It's a timely, relevant study," said Linda McCauley, dean and professor of Emory University's Nell Hodgson Woodruff School of Nursing. McCauley was not involved in the study.

Researchers have long suspected pesticides may play a role in the elevated cancer rates among farmers and others who apply pesticides.

Using data from the same Agricultural Health Study group, in 2003 researchers reported about a 14 percent higher prostate cancer incidence than the general population of men in Iowa and North Carolina. The fumigant methyl bromide was most strongly associated with prostate cancer. Use of chlorinated pesticides, such as DDT, was linked to cancer for applicators over 50 years old.

Then, in 2013, using the same study group, researchers found that men exposed to certain pesticides—fonofos (taken off the market in 1998), terbufos and malathion—were more likely to develop aggressive forms of prostate cancer.

The current study, published last month in the journal "Environmental and Molecular Mutagensis," sought to provide evidence on how pesticides might promote cancer. It included 596 male pesticide applicators. Men who experienced a “high pesticide exposure event," meaning a spill or other accident that would leave them highly exposed, were more likely to have elevated levels of DNA methylation in a gene linked with increased prostate cancer risk.

This type of exposure to pesticides would be “unusually high," said lead author Dr. Jennifer Rusiecki, an assistant professor of medicine at Uniformed Services University in Maryland.

Proper DNA methylation controls a number of important processes in our body, including regulating how genes are expressed. Certain genes, including ones examined in this study, commonly have elevated DNA methylation during certain cancers.

Almost a quarter of the men surveyed reported a high pesticide exposure event in their past. It's not entirely clear how the pesticides may induce these DNA changes. Rusiecki said it could be through oxidative stress, a molecular change that can damage DNA known as alkylation, or disruption of the body's hormones.

The new study was limited in that the high pesticide exposure was self-reported and wasn't specific to any particular pesticides, Rusiecki said, so it's unclear what the applicators were exposed to.

Farming carries other risk factors beyond pesticides as well. There are other exposures—gasoline and diesel emissions, solvents, dusts, oils and microbes—that are higher than the average person. Family history plays an important role in men's susceptibility to prostate cancer as well.

However the study bolsters what many researchers suspect, McCauley said.

“Our entire pesticide regulatory system is built on neurotoxicity and poisonings," she said. But many chemicals that don't necessarily prove acutely toxic can inconspicuously harm the body over time.

“There are changes that happen to the body before we kill the body," said McCauley, who helps communicate pesticide research to migrant farmworkers. “It's really sad how [farmworkers] are told 'don't worry, there's not a problem,' when they know that working around these chemicals cannot be healthy for them."

Personal protection equipment is not enough to protect farmworkers health, said Nishelle Harriott, science and regulatory director of Beyond Pesticides, which advocates for phasing out harmful pesticides.

“Long sleeve shirts, gloves are considered personal protective equipment," she said. “Those things wouldn't do much for someone breathing these chemicals in."

“Big setback"

Harriott's organization and many others have long pushed for the phase-out of harmful pesticides, but the new Trump Administration may make their job difficult.

The president has repeatedly talked about reducing government interference and regulation. His appointee for Secretary of Agriculture, Georgia governor Sonny Perdue, has been an advocate of pesticides in the past and voted to get rid of laws targeting agricultural pollution in his state.

Trump's pick to run the U.S. Environmental Protection Agency, which regulates and registers pesticides, is Oklahoma Attorney General Scott Pruitt, who has made a career fighting the agency over its regulation of pollution.

The U.S. Centers for Disease Control and Prevention found that Pruitt's home state leads the nation in pesticides deaths and illnesses, according to analysis of data from 2000 to 2010.

The EPA is currently reviewing a number of controversial pesticides, including glyphosate, atrazine and neonicotinoids. In the most immediate case, the agency has until March 31 to rule on Dow AgroSciences' chlorpyrifos, a chemical widely used on a variety of crops such as corn, asparagus, broccoli and soybeans. The agency's risk assessments found the chemical is not safe.

Over the past two decades many environmental groups have asked for a ban over concerns regarding impacts to children's development.

The new administration is a “big setback," said Emily Marquez, a staff scientist at the Pesticide Action Network.

“We have to make sure we're sticking up for people threatened by any policies that might affect people like pesticide applicators, or people that live near farms that use pesticides."

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