Nearly 300 chemicals linked to breast cancer-contributing hormones in everyday products
Elizabeth Gribkoff for Environmental Health News
Of those chemicals, 219 had not been previously identified
as potential carcinogens, Ruthann Rudel, director of research for the Silent
Spring Institute and co-author of the new study, told EHN. The findings come in
a study out this
week in Environmental Health Perspectives.
While scientists have known for decades that higher levels
of estrogen and progesterone are linked to breast cancer, experts say that
safety screening to test U.S. consumer products rarely looks at how chemicals
affect the production of those hormones.
"The way that chemicals are tested now, they are really
missing breast-related effects," said Rudel. "We have to do a much
better job checking for these effects when we test chemicals."
Environmental chemicals and hormone production
Scientists have historically used animal studies to understand whether chemicals pose a threat to humans. Animal studies take time and money, though, leading researchers and regulators to increasingly use high-throughput tests to more quickly screen chemicals for hormone disruption and other potentially disease-inducing effects.
With these high-throughput
tests, researchers expose cells and other molecules to chemicals to see whether
they trigger any changes.
Researchers from the Silent Spring Institute, a non-profit
that studies the environmental causes of breast cancer, decided to look
through 2018 EPA ToxCast safety data on
roughly 1,800 chemicals to see how many caused cells to increase estrogen and
progesterone.
Laura Vandenberg, associate professor of environmental
health sciences at the University of Massachusetts Amherst who was not involved
in the study, told EHN that one of the characteristics toxicologists commonly
look for is whether a chemical mimics
estrogen. To date, though, there has been little focus on whether
chemicals could actually cause cells to produce more estrogen or progesterone.
Rudel and a colleague found that 296 chemicals increased one or both of the hormones. Some of the hormone-increasing chemicals include the pesticide atrazine, the fungicide imazalil, and hair dye ingredient 1-4, benzenediamine.
Vandenberg said she was disturbed but not shocked to see that
so many of these chemicals increase hormone production in cells as "many
of these chemicals (like pesticides) were designed to be biologically active."
The Silent Spring researchers then looked through carcinogen and reproductive toxicity databases, like California's Prop 65 list, to see which of these chemicals were already on those lists.
The researchers found that roughly
a third had been identified as carcinogenic, toxic to development and
reproduction, or both. But they also found that many of the chemicals on their
list "hadn't been tested or evaluated," for impacts to those systems,
Rudel said.
Scientists have known for some time now that estrogen and
progesterone contribute to breast cancer because both hormones stimulate breast
cell growth, increasing the risk of uncontrolled cell growth and DNA damage.
Around 70% of breast cancer cases respond to these hormones, and treatment for
this disease commonly involves using drugs that inhibit estrogen.
"What we know is that a woman's own production of
estrogen is actually one of the biggest risk factors for breast cancer,"
Vandenberg said, adding that early puberty and delayed menopause, which give
the body more time to produce estrogen, have been linked to higher rates of
breast cancer.
Women’s health focus
Rudel said that their list of hormone-increasing chemicals
provides a good starting point for both toxicity and human exposure research.
"There hasn't been a super systematic approach to what chemicals should be
studied in breast cancer (epidemiological) studies," she added.
The researchers also found that even for chemicals that had
been previously scrutinized, past risk often didn't look at or dismissed
mammary gland impacts. For example, although a multi-generational toxicology
study showed that exposure to dichlorophenol, a chemical in some pesticides and
disinfectants, stiffened and whitened breast tissue in all doses, the authors
of that study didn't take those effects into consideration when determining
what a safe dose of that chemical is.
And a lot of the animal tests used by regulators only look
at a couple of the hundreds of ducts in the mammary gland, which is
"treated as sufficient—and it's not," Vandenberg said.
"My worry is that women's health always gets sort of
short shrift, and there's a little bit of an attitude of breast cancer as a
disease of the old, and therefore, it's not a priority for regulatory
agencies," she said, stressing that no one at those agencies had actually
said that.
How to limit your chemical exposure
Researchers also don't have a great sense of how we're
exposed to many of the chemicals on the list, Rudel added.
Silent Spring has a mobile app, Detox Me, that allows
people to scan consumer product barcodes and other features to try to minimize
their exposure to toxic chemicals.
