Researchers have identified 17 types of toxic chemicals that can lead to mammary tumors in animals, suggesting that cancer-prevention efforts should include warning women about avoiding exposure to these substances.

A new peer-reviewed study says that many chemicals demonstrated to cause mammary cancer in rats are linked to breast cancer in women.

The study, published in the National Institutes of Health (NIH) journal Environmental Health Perspectives, was conducted by scientists at the Silent Spring Institute.

According to the researchers, their findings validate and expand on findings from other leading authorities, including the International Agency for Research on Cancer (IARC), which has expressed that “it is biologically plausible that agents for which there is sufficient evidence of carcinogenicity in experimental animals also present a carcinogenic hazard to humans.”

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The chemicals the researchers identified are found in gasoline, diesel and other vehicle exhaust, flame retardants, stain-resistant textiles, paint removers, and disinfection byproducts in drinking water.

Gasoline and chemicals formed by combustion (for example, benzene and butadiene) are among the largest sources of mammary carcinogens in the environment, according to the researchers. Exposure comes from vehicles, lawn equipment, tobacco smoke, and charred or burned food. Other mammary carcinogens include solvents, such as methylene chloride and other halogenated organic solvents used in spot removers, specialty cleaners, and industrial degreasers; pharmaceutical hormones such as hormone replacement therapy; certain flame retardants; a chemical used in stain-resistant textiles and nonstick coatings; and styrene, which is in tobacco smoke and is also used to make Styrofoam. Drinking water can contain mammary carcinogens, such as byproducts of disinfection or solvents that are common well water contaminants.

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Lead study author Ruthann Rudel, M.S., research director of the Silent Spring Institute in Newton, Mass., told Healthline, “With so many women diagnosed with breast cancer, there is really an urgent need for prevention. We found that rodent studies are a good way to predict which chemicals can cause breast cancer in people.”

Emphasizing that it has been known that chemicals cause mammary tumors in rodents, Rudel said that very few of these chemicals are studied in women. “We found that when we do have studies in people, animal evidence is consistent with the human evidence. We expect this, but the review is evidence that the chemicals that cause mammary tumors in rodents are the important ones to pay attention to in people, either by reducing exposure or conducting follow-up studies.”

The researchers identified 102 priority chemicals and consolidated them into what Rudel dubbed “17 chemical groups” that are similar based on properties or their exposure sources.

“For people who are conducting big studies looking at breast cancer in women, many of them have blood or urine samples from these women that have been stored. Now, we’ve produced measurement methods so they can say, ‘I have some people who may be exposed to these five chemicals’ and use a method to measure exposure to them in blood. It’s a toolkit for researchers.”

Rudel explained that the study’s findings are important for product manufacturers and retailers, as well as for policy makers. “It’s something to consider in terms of chemicals to avoid or minimize in products, or look for alternatives. For policy makers, it’s an opportunity to develop programs to limit exposures to these chemicals and to encourage safer alternatives,” she said.

She added that there are programs in the U.S. that are monitoring chemical exposures in the population: “This list and these tools of measurement methods can help direct programs to look for exposures that may be really important for breast cancer. Who is highly exposed, are there certain occupations, are there certain age groups, and certain parts of the country?”

The National Institutes of Health is expected to incorporate the study’s recommendations in its study of 50,000 women on the causes of breast cancer.

Julia Brody, Ph.D., study author and executive director at Silent Spring Institute, said in a press statement, “Every woman in America has been exposed to chemicals that may increase her risk of getting breast cancer. Unfortunately, the link between toxic chemicals and breast cancer has largely been ignored.”

She added that reducing chemical exposures could save many women’s lives. “When you talk to people about breast cancer prevention, chemical exposure often isn’t even on their radar. Studies that address toxic chemical exposure account for just a drop in the bucket of money spent on breast cancer,” she said.

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  • Reduce exposure to fumes from gasoline. Limit exposure to exhaust from diesel or other fuel combustion, for example, from vehicles or generators. Don’t idle your car. Use electric, instead of gas powered, lawn mowers, leaf blowers, and weed whackers.
  • Use a ventilation fan when you cook and limit consumption of burned or charred food.
  • Don’t buy furniture with polyurethane foam; or ask for foam not treated with flame retardants. California’s decision to repeal its requirement that foam in furniture be flame-resistant is expected to result in an increased availability of flame retardant-free furniture in the U.S.
  • Avoid stain-resistant rugs, furniture, and fabrics.
  • Use a dry cleaner who doesn’t use PERC or other solvents; ask for “wet cleaning.”
  • Buy a solid carbon block drinking water filter.
  • Reduce exposure to chemicals in house dust by removing shoes at the door, using a vacuum with a HEPA filter, and cleaning with wet rags and mops.