New research finds 485 chemicals in US pesticide products linked to breast cancer

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

What the review found

The researchers found the chemicals not only in pesticides used on crops, but also in lice treatments applied to children's scalps, home lawn fertilizers, and flea and tick treatments. Only about 145 of the identified chemicals are registered with the Environmental Protection Agency (EPA) as active ingredients, which the authors say points to the use of inert status or other loopholes.

The review also covers hundreds of so-called “inert”, or inactive, ingredients that typically do not undergo a thorough safety review. They are usually added as surfactants or penetrating agents; about 4,000 inert ingredients are approved by the EPA, among them PFAS, known as “forever chemicals”.

A regulatory blind spot

The EPA considers each ingredient's individual health risks and does not assess the whole formula, or combined exposure to multiple pesticides. “They are not biologically inert, they are just called inert because they do not target the pest,” said Jenny Kay, a co-author with the Silent Spring Institute non-profit. “It is a regulatory blind spot,” she added. The EPA in 2023 rejected a petition to review inert ingredients more stringently.

Kay also pointed to hormone-disrupting chemicals that can cause disease at lower levels of exposure but not higher. “Adding these exposures up gets pretty consequential and concerning,” she said. “We wanted to bring more attention to the pesticides in different products.”

Why it matters

Besides skin cancers, breast cancer is the most commonly diagnosed cancer in the US. Incidence has risen by about 1% per year, according to the American Cancer Society, and slightly faster among women younger than 50 (1.4%). Federal NHANES data shows 84 of these chemicals are present in the general population, though scientists say that is an undercount.

The review is part of a broader effort by the Silent Spring Institute to map where people are exposed to such chemicals. It identified about 500 in consumer goods and 462 in drinking water, and called for expanding California's Proposition 65. A recent report also 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.