Study identifies 485 breast cancer-linked chemicals in US pesticide products

EPA reviews individual ingredients only, not cumulative exposures or formulas

A peer-reviewed paper published in Environmental Health Perspectives, a journal of the American Chemical Society, identified at least 485 chemicals in US pesticide products linked to breast cancer. The findings raise questions about the safety of food and other products at a time when early-onset breast cancer rates are rising worldwide.

The research, by the Silent Spring Institute, a nonprofit, identified chemicals not only in agricultural pesticides but also in lice treatments applied to children’s scalps, in home lawn fertilizers, and in flea and tick treatments.

“Adding these exposures up gets pretty consequential and concerning,” said Jenny Kay, a paper co-author with the Silent Spring Institute. “We wanted to bring more attention to the pesticides in different products.”

Among the 485 chemicals identified, only about 145 are registered with the EPA as active ingredients, the researchers found. The remainder are classified as “inert” ingredients — substances added as surfactants or penetrating agents that help disperse the active ingredients or make them more absorbable. About 4,000 inert ingredients are approved for use by the EPA, including PFAS “forever chemicals.”

“They are not biologically inert, they are just called inert because they do not target the pest,” Kay said. “It is a regulatory blind spot.”

The EPA in 2023 rejected a legal petition to begin more stringent reviews of inert ingredients, according to Kay. The agency’s regulatory framework considers each pesticide ingredient’s individual health risks but does not consider the full pesticide formula or exposure to multiple pesticides, the paper states.

Federal health data from the National Health and Nutrition Examination Survey shows that 84 of the breast cancer-linked chemicals identified are present in the general population. Scientists said that figure is an undercount, since the survey does not track most of the 485 compounds identified.

The pesticide review is part of a broader systematic effort by the Silent Spring Institute to identify breast cancer-linked chemicals across the economy and everyday life. The institute previously identified about 500 such chemicals in common consumer goods and 462 in drinking water.

Beside skin cancers, breast cancer is the most commonly diagnosed cancer in the United States. Incidence rates have risen by 1% per year, according to the American Cancer Society, with the increase slightly faster — 1.4% — among women younger than 50.

Kay pointed to another regulatory gap: some hormone-disrupting chemicals cause disease at lower levels of exposure but not at higher levels, a pattern known as a “non-monotonic dose response.” That phenomenon, she said, has led the EPA to dismiss some chemicals’ risks and to ignore the possibility that those chemicals cause cancer at low levels.

The paper also notes that top officials in the EPA’s pesticide and chemical safety offices are former industry lobbyists, and characterizes the pesticide office as having been viewed as heavily infiltrated by industry and subject to its influence.

“I’m not in the head of EPA scientists, but I do worry a lot about industry pressure and the revolving door between EPA and industry employees because all of that factors into the way the EPA considers and regulates chemicals,” Kay said.

The Silent Spring Institute called for an expansion of California’s Proposition 65, which requires warnings for chemicals known to cause cancer or reproductive harm. The study identified 16 pesticides that are not listed under Prop 65 and the authors argue that adding those chemicals could discourage companies from using them.

Separately, a recent report found that about 25% of the nation’s water intake and roughly 675,000 wells draw water contaminated with dangerous levels of atrazine, a hormone-disrupting chemical linked to breast cancer. Water-filtration systems can remove many pesticides from water, with activated carbon and reverse osmosis among the more effective methods, though no system is perfect.

For consumers seeking to reduce exposure, the paper recommends buying organic produce or untreated products when possible. A Consumer Reports guide lists fruits and vegetables with typically high pesticide residues, including blueberries, watermelon, kale, and green beans.