Bisphenol A has gotten a much higher profile in recent years, as the "BPA-free" label adorns an increasing number of water bottles and baby products. News headlines regularly hint at possible connections between BPA and a lengthening list of health problems. But the ingredient is still common in plastics, food can liners -- and in our bodies.
The chemical can be found in 93 percent of Americans, according to a guide released Monday by the nonprofit Environmental Working Group and the Keep-A-Breast Foundation. And BPA is just one of many everyday chemicals that even at very low levels could harm our bodies by mimicking or blocking the natural hormone messengers responsible for everything from sleep and metabolism to growth and reproduction.
"We're seeing more and more of these chemicals," said Johanna Congleton, senior scientist with EWG.
The groups' new "Dirty Dozen" guide to what they deem the worst endocrine-disrupting chemicals lists ingredients that can be found in rocket fuel, brake fluid, flame retardants, herbicides and non-stick frying pans, as well as notorious carcinogens and neurotoxins such as lead, arsenic and mercury.
"It's not just BPA," Congleton said. "Dioxin, for example, interacts with receptors in charge of development in the womb, the way the digestive system works, puberty. At the same time, we're exposed to a mixture of these chemicals."
But not everyone is convinced that endocrine disruptors pose a public health risk, and the science is complicated, to put it lightly. With widespread debate about tighter regulation of toxic chemicals, including endocrine disruptors, the stakes are high for both industry and society -- much as they were when criticisms first arose over lead paint and tobacco.
Proposed European Union policy, for example, could influence the global manufacture of endocrine disruptors. That debate escalated this July when 18 scientists published an editorial arguing that the EU rules, outlined in a leaked draft, were "based on virtually complete ignorance of all well-established and taught principles of pharmacology and toxicology." An onslaught of charged responses from hundreds of doctors and toxicologists ensued. Meanwhile, an investigative report by Environmental Health News in September found that 17 of the 18 authors of the original editorial had industry ties.
Andrea Gore was the lead author of one response, published in the September issue of Endocrinology, which pointed to "thousands of published studies," as well as recent reviews by the United Nations and World Health Organization, that found endocrine disruptors are "active at very low doses and can induce a range of adverse health outcomes many of which are not examined in traditional toxicology assays."
"There's so much evidence now that for people to deny this is happening, in my opinion, is very disingenuous," said Gore, a professor of pharmacology and toxicology at The University of Texas at Austin.
"You can always find a paper that contradicts a finding," she added. "But if you have one out of 101 papers finding something, that's very different than 100 of 101."
One of the more controversial topics in the field is the possibility that even tiny amounts of endocrine disruptors can profoundly affect the body. A small perturbation in the balance of natural hormones, experts note, has long been known to pose potentially devastating health consequences.
"We've understood for some time the importance of having normal hormone levels," said Gore. "We need the right levels at the right times to lead healthy lives."
This is particularly critical during certain periods of development, such as during fetal development. The Endocrine Disruptor Exchange, which is now celebrating its 10-year anniversary, has released an updated chart identifying "critical windows of development" during which a growing fetus is especially sensitive to tiny doses of hormone mimics.
Regulations, however, have been traditionally written to identify general thresholds for safe exposures, explained Carol Kwiatkowski, executive director of the nonprofit research group and an adjunct at the University of Colorado Boulder. If future rules go against the familiar paradigm of "the dose makes the poison" in favor of acknowledging no safe threshold for the chemical class, the implications could be vast.
"Endocrine disruptors turn everything on its head," added Kwiatkowski, "and that makes people nervous."
Accumulating evidence also suggests that exposure to endocrine disruptors could pass harm down to later generations. A study published in January found that descendants of rats exposed to BPA developed disease. The third generation had "significant increases" in pubertal abnormalities, testis disease, ovarian disease and obesity. Another suspected endocrine disruptor, DDT, made headlines last week after the release of a study suggesting the insecticide may have played a role in high rates of obesity among rats three generations after exposure.
Industry representatives, in response to questions from The Huffington Post, remained critical of the proposed EU regulations and emphasized uncertainties in the science over BPA, phthalates and other chemicals highlighted in the new guide.
"Unfortunately, recent EU proposals for regulating endocrine disruptors are based on a narrow, hazard-based approach that offers only a one-sided and incomplete view of potential health and environmental risks," Scott Jensen, spokesman with the American Chemistry Council, told HuffPost in a statement. "ACC believes the best approach is one that is risk-based and considers both hazard characterization and exposure."
"ACC is committed to constructively engaging with the scientific community and regulatory agencies to enhance the scientific understanding of chemicals and how they may interact with the endocrine system," he added, noting the group continues to advise the U.S. Environmental Protection Agency on screening and testing chemicals.
Experts consulted by HuffPost agreed that many questions about the actions and adverse effects of endocrine disruptors remain unanswered. The point of disagreement seems to hinge on how best to proceed based on the available evidence.
Laura Vandenberg, an endocrine disruptor researcher at the University of Massachusetts, Amherst, expressed her frustration with the pace of policy and the influence of industry.
"We see some of the same tactics: hiring experts, seeding doubt, well-planned press releases," she said, citing previous battles waged over lead and cigarettes. Endocrine disruptors pose a far more complicated challenge, given the sheer breadth of the implicated products and their potential health impacts.
While Vandenberg cheered the efforts of the Environmental Working Group in raising consumer awareness about the dozen chemicals and how best to avoid them, she said the new guide also further rouses her impatience with regulators.
"We're still having the conversation about what consumers should be doing, when realistically consumers can't avoid these chemicals," added Vandenberg, who was among 41 scientists who authored another rebuttal to criticism of the EU proposal. "A mom shouldn't have to be a chemist to go to the grocery store."
Joel Tickner, an environmental health expert at the University of Massachusetts, Lowell, discussed the difficulty of controlling these products at the policy level.
"We're exposed to a lot of endocrine disruptors. The effects are cumulative," said Tickner. "There's really no way to regulate chemicals in products easily without substituting."
But that doesn't mean manufacturers should swap out BPA for something like bisphenol S, a close chemical cousin that has shown signs of similar, if not greater, toxicity. Rather, Tickner echoed previous calls for a new green chemistry, in which products are designed from the ground up to minimize the use of hazardous substances.
Vandenberg is in the initial phases of starting her own lab, which she pledges will not focus on BPA. "If you look at how much money, time and effort has gone into this one chemical, it's ridiculous," said Vandenberg, who has spent years studying BPA.
"We know enough about this chemical," she said. "We know its effects at low doses. We know its concerning effects on organs. The evidence is overwhelming."
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