Dozens of pesticides linked with mammary gland tumours in animal studies

In an analysis of how regulators review pesticides for their potential to cause cancer, researchers at Silent Spring Institute have identified more than two dozen registered pesticides that were linked with mammary gland tumours in animal studies. The new findings are said to raise concerns about how the US Environmental Protection Agency (EPA) approves pesticides for use and their role in the development of breast cancer.

“We know pesticides like DDT increase breast cancer risk, so we decided to look into it,” said co-author Ruthann Rudel, an environmental toxicologist and Director of Research at Silent Spring. “After examining pesticide registration documents from EPA, we found two separate studies in which rodents developed mammary gland tumours after being exposed to triclopyr, yet for some reason regulators dismissed the information in their decision not to treat it as a carcinogen.”

When manufacturers apply to register a pesticide, EPA reviews existing studies and assigns the chemical a cancer classification (how likely or unlikely the chemical is to cause cancer). After reviewing triclopyr, the Silent Spring researchers wanted to review other pesticides.

Rudel and Silent Spring scientist Bethsaida Cardona reviewed more than 400 EPA pesticide documents summarising the health effects of each. They found a total of 28 pesticides linked with mammary gland tumours, with only nine having EPA acknowledgement of them as causing mammary tumours.

Rudel and Cardona also found that many of the pesticides in their analysis behaved like endocrine disruptors, by interfering with oestrogen and progesterone. “Breast cancer is highly influenced by reproductive hormones, which stimulate the proliferation of cells within the breast, making it more susceptible to tumours,” said Rudel. “So, it’s important that regulators consider this kind of evidence. If they do not, they risk exposing people to pesticides that are breast carcinogens.”

“In light of our findings, we hope EPA updates its guidelines for assessing mammary gland tumours by considering evidence that more completely captures the biology of breast cancer, such as the effects of endocrine disruptors,” said Cardona.

Rudel and Cardona recommend that EPA re-evaluate five pesticides in particular – IPBC, triclopyr, malathion, atrazine and propylene oxide – due to their widespread use and the evidence uncovered in the new analysis.

An EPA spokesperson said: “Per the agency’s cancer classification guidelines, the agency does not consider tumours that are not treatment related to be adverse.” EPA noted that it performs an independent review of studies conducted in mice and rats to evaluate the carcinogenic potential of pesticides. The results of the independent review are peer-reviewed by the Cancer Assessment Review Committee (CARC) which considers a variety of information and their recommendation is not based on the results of one study, but on the results of all studies that are available, according to EPA.

Pesticides are evaluated not only to determine if they cause cancer in laboratory animals, but also as to their potential to cause human cancer, EPA continued. For more information on this process, EPA said to please visit: https://www.epa.gov/…