The BPA in your water bottle may be even more dangerous than you think.

A major new paper is raising the alarm about low-level exposure to endocrine disruptors, substances like bisphenol A (BPA) and phthalates that interfere with hormones in the human body. These endocrine-disrupting chemicals, or EDCs, are found in a vast array of everyday products like plastics, household cleaners, cosmetics, pesticides, upholstery, and paper receipts.

“The dose makes the poison” is a widely accepted tenet in the field of toxicology, suggesting that a substance’s impact on the body increases with the amount of exposure. Case in point: A drop of arsenic in a well may not produce any noticeable health problems; a generous pour mixed into lemonade can kill a man.

Get ready for a change in accepted dogma: A paper published in the journal Endocrine Reviews found that low doses of EDCs — amounts that average people are exposed to through consumer products every day — can have serious negative health impacts.

“This is the biggest and broadest review of this work that’s been done to date,” says Laura Vandenberg, lead author of the paper and a post-doctoral fellow at the Tufts Center for Regenerative and Developmental Biology. She and a team of 11 other scientists combed through 840 scientific studies that examined dozens of EDCs’ low-dose impacts.

“At high doses [like in industrial accidents], endocrine-disrupting chemicals can kill people, cause birth defects and severe malformations of fetuses,” says Vandenberg. “These studies overwhelmingly show that EDCs have actions at low doses, too. They’re not killing people, but instead they are changing the development of organs that can have permanent effects.” For example, low-level EDC exposure has been linked to cancers, obesity, infertility, neurobehavioral disorders, and immune-system issues, among other health problems.

Further complicating the picture, some EDCs produce one effect at a low level of exposure and a totally different effect at a high level, or even no effect at all — a relationship known as non-monotonicity.
To illustrate a non-monotonic effect, Vandenberg points to PCBs, compounds that, while no longer used regularly, still persist in the environment. “If you have the highest doses of PCBs, you’re not at the highest risk,” says Vandenberg. “It’s actually people who have moderate levels that are more likely to get things like cardiovascular disease.”

Another example is tamoxifen, a drug used to treat breast cancer. At high doses, this hormone disruptor inhibits breast-cancer growth. At low doses, it actually stimulates it.

“The assumption has always been that if a little is bad, a lot more is worse, and it’s all dose-related,” says Patricia Hunt, a reproductive biologist at Washington State University who was not involved with Vandenberg’s paper. “That’s not how hormones work, and that’s not how endocrine disruptors work. These non-monotonic dose responses aren’t a rare thing — they’re an expected thing for endocrine-disrupting chemicals.”

Of course, not everyone agrees with the assessment by Vandenberg et al. The American Chemistry Council, an industry group, isn’t convinced that low doses of endocrine disruptors harm human health. “[R]egulatory agencies around the world, which review extensive scientific data, have not confirmed the validity of low-dose effects or their relevance to human health,” ACC spokesperson Kathryn St. John said via email.

It’s no wonder the industry isn’t happy with the research: Getting EDCs out of plastics, pesticides, and other widely used products would be a massive undertaking.
“It’s terrible and it’s frightening, but in pretty much every aspect of our lives, we’re being exposed to these chemicals,” Vandenberg says.

She and other concerned scientists hope that this paper will spur regulation of EDCs, as well as more comprehensive research. “If regulators are going to read the paper and really pay attention to it, it should change the regulation of endocrine-disrupting chemicals,” says Shanna Swan, a professor of preventive medicine at the Mount Sinai School of Medicine. “I don’t think it’s avoidable after reading this — the way chemicals are regulated is not protecting health.”

Several states have already banned BPA in children’s products. More change is being driven by consumer pressure. Most baby-bottle makers have voluntarily phased out BPA, and some food manufacturers are starting to do the same. These are small steps forward on just one of dozens of EDCs Americans are regularly exposed to, but they show what’s possible with enough pressure.

“Regulatory agencies that are charged with protecting the American people and the world need to think about how we test chemicals for these low-dose effects,” says Vandenberg. “Can a chemical that mimics a hormone ever be used safely? We really believe that chemicals that act like hormones are not products that should be in our bodies. We need to think about phasing them out, replacing them and changing the way we test chemicals that are coming onto the market now.”