Cancer risk doubles for Iowa, NC pesticide applicators who used carbaryl, study finds

Listen to the audio version of this article (generated by AI).

Pesticide applicators in North Carolina and Iowa who sprayed the insecticide carbaryl often during their career have a higher risk of getting stomach, esophageal, tongue and prostate cancers, according to new research led by the National Cancer Institute (NCI). 

The research is the first to link the pesticide to stomach cancer, but it builds on many previous studies that have found carbaryl — often marketed under the brand Sevin — increases risk for multiple other cancers. The chemical is used to kill aphids and other insects on various farm crops, as well as insects such as ants, fleas and ticks in turf and home gardens. 

“This is the largest and most comprehensive prospective evaluation of carbaryl and cancer risk to date,” the authors wrote.

The researchers used data from the US government-funded Agricultural Health Study about pesticide use by farmers and other licensed pesticide applicators in Iowa and North Carolina. The data includes self-reported pesticide use from 1993 to 1997 and from 1999 to 2005.

“This is the largest and most comprehensive prospective evaluation of carbaryl and cancer risk to date.” – Study authors

Study senior author Laura Beane Freeman, a senior NCI investigator, said the researchers not only looked at how many days applicators reported spraying the carbaryl, but factors that might impact exposure, such as what personal protective equipment they did or didn’t use and how they applied the pesticide.

The researchers also looked at state cancer registries in 2014 for North Carolina and in 2017 for Iowa. 

Applicators who reported the most days spraying carbaryl and intense exposure were about twice as likely to develop stomach cancer compared to those who reported they never sprayed it. The highest exposure group also had a 52% higher incidence of esophageal cancer and 91% higher incidence of tongue cancer compared to those who reported they never sprayed carbaryl, the study found. 

The highest exposure group had a 56% higher incidence of prostate cancer for exposures that were more than 30 years prior to the cancer being diagnosed. 

It is “tragic that we allow products like this to be registered for use and we keep them on the market despite mounting evidence of health harms,” said Alexis Luckey, the executive director of Toxic Free NC, which has advocated for pesticide reform in the state for nearly four decades.

“Pesticide applicators and farmworkers in the fields … pay the highest price in this flawed system,” Luckey said.

Pesticides and cancer 

Numerous studies have linked carbaryl to various types of cancer. And a 2021 regulatory safety data sheet for the chemical, made and sold for years by Bayer in the Sevin brand, warns that the product is “suspected of causing cancer.” 

The new study adds to growing evidence that many commonly used farm chemicals are making people sick. In a national analysis last year, researchers found pesticide exposure may rival smoking for cancer risk. 

“These results are not surprising,” Luckey said. 

Just last month, researchers started conducting “listening” sessions around Iowa as part of a new project to investigate potential environmental causes for what some call a cancer “crisis” in the state, which has the highest rate of cancer in the nation and is only one of two US states where cancer is increasing. 

“Pesticide applicators and farmworkers in the fields … pay the highest price in this flawed system.” -Alexis Luckey, Toxic Free NC

Freeman said more work is needed to better understand how carbaryl might cause cancer. However, the insecticide has been shown to react with nitrate and nitrites — both of which people can consume from food and water, especially in heavily agricultural areas — to form cancer-causing compounds. Some studies suggest carbaryl can damage DNA and chromosomes as well, which could lead to cancers.

Brandon Herring, a spokesperson for the North Carolina Department of Agriculture & Consumer Services, said the agency hasn’t reviewed the study but that it “serves as a reminder of the established safety guidance, such as application rates and methods, that are on each pesticide’s label. We encourage people to follow that guidance.” 

Carbaryl regulation 

There are 61 registered pesticides on the market that contain carbaryl, according to the US Environmental Protection Agency. While the insecticide is still widely used in the US, Europe banned all uses in 2007 over cancer concerns. 

The researchers in the current study estimated that roughly 700,000 pounds of carbaryl are applied in the US each year on farm crops. Freeman said an estimated two million pounds are applied near buildings, and on turf, pastures and roadways annually. 

It’s not just humans that could be at risk: the EPA is changing labels on carbaryl products after the US Fish and Wildlife Service found that it “was likely to jeopardize 78 listed species and adversely modify 14 critical habitats when used as currently registered.” 

The new labeling, scheduled to be completed by the end of the year, is designed to reduce runoff and drift, and will alert applicators to restricted and sensitive areas. 

Drexel Chemical Company and Tessenderlo Kerley, Inc., two agricultural companies that produce carbaryl products, did not return requests for comment on the new study.

Featured photo: US Forest Service employee spraying carbaryl. (Credit: USFS)