Pesticides used near farm communities tied to rare but deadly childhood cancer

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Children whose mothers lived near farms and fields treated with certain pesticides during pregnancy have a higher risk of a deadly cancer that is most commonly found in infants before their first birthday, according to a new study. 

The new study, published in the Environmental Research journal, found that pregnant women in California who lived near areas that were treated with insecticides — flonicamid, cypermethrin or permethrin — or a now-banned fungicide called benomyl were more likely to have babies that would suffer from neuroblastoma, a cancer of the nerve cells that is seldom diagnosed after the age of five. 

While considered rare — there are about 600 to 800 new cases each year in the US — it is the most common cancer in infants and accounts for about 15% of US child cancer deaths each year. 

Previous studies have found an association between some pesticides and neuroblastoma, but this is the first to examine links between prenatal exposure from specific sprayed pesticides near the home and the disease. 

“Just knowing the pesticides broadly might be linked to cancer doesn’t provide an actionable strategy,” said Julia Heck, senior author of the study and a professor and epidemiologist at University of North Texas. “We wanted to know which are the bad actors.”

Heck and colleagues looked at data of more than 200,000 children born in California from 1998 to 2016, including 199 children who had neuroblastoma. They used the state’s pesticide use reporting system to estimate the mothers’ exposure to dozens of different pesticides that have previously been linked to cancers. Prenatal exposure to flonicamid, cypermethrin, permethrin and benomyl was associated with a 33%, 53%, 24% and 20% increased risk, respectively, for neuroblastoma after birth compared to babies that had no estimated exposure to those pesticides.

“Just knowing the pesticides broadly might be linked to cancer doesn’t provide an actionable strategy. We wanted to know which are the bad actors.” – Julia Heck, University of North Texas

Flonicamid and cypermethrin are largely used to kill insects on cotton and some crops. The most recent data on use shows that both are sprayed in California’s Central Valley. Cypermethrin use declined sharply since peak use in the early 1990s. Permethrin, used to control insects on crops and at orchards, is heavily used in California’s Central Valley region, and is also commonly used to control mosquitoes via treated clothing or sprays. 

Amy MacPherson, deputy director of outreach and communications for the California Department of Pesticide Regulation (DPR), said the study’s use of proximity to pesticide applications as a proxy for exposure is “a useful starting point, [but] it does not account for important factors such as the chemical properties of individual pesticides, actual exposure levels, or other potential risk factors for neuroblastoma.”

She said while cypermethrin and permethrin tend to bind to soil — making them less likely to become airborne — the state included them in its pesticide air monitoring effort published in 2023. Both “were detected only a handful of times, and always at trace levels far below DPR’s health-based screening levels,” she said. Flonicamid was not included in the report. 

Benomyl was banned in the US in 2001 due to concerns over how toxic it was. Heck said finding benomyl’s potential link to neuroblastoma decades after its ban shows how difficult it is to study pesticides’ health harms. 

“There are bans, pests become resistant, pesticide companies come out with new formulations,” Heck said. “It’s hard to stay on top of something that changes so fast.”

Suspected carcinogens

In its most recent human health assessments the US Environmental Protection Agency (EPA) classified both flonicamid and permethrin as having “suggestive evidence of carcinogenic potential” and cypermethrin as a “possible human carcinogen.”

The agency, however, did not assess potential hazards from nearby spraying of permethrin or cypermethrin, saying there is no need because exposures from people using it around their home, which were assessed, would be greater. For both chemicals the agency concluded “there are no risks of concern” for residential uses or from spray drift from the chemicals. 

For flonicamid, however, the agency acknowledges “spray drift is a potential source of exposure to individuals who are located in close proximity to pesticide applications.” 

The EPA could not be reached for comment on the new study because of the federal government shutdown. 

Heck said she hopes the work catches the attention of the EPA or international bodies like the World Health Organization to better address pesticide harms. “We’re trying to add evidence that will ideally allow them to take action,” she said. 

MacPherson said DPR reviews new studies like this one as part of their ongoing oversight.

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