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NC Scientists in the Middle of the BPA Debate

The FDA ruled late last week not to ban plastic additive bisphenol A (BPA) from many products on the market. But local scientists find the data on BPA are more troubling. Also, see our Q&A with NIEHS director, Linda Birnbaum.

By Stephanie Soucheray

Researchers in North Carolina now find themselves squarely in the middle of a scientific controversy after a ruling by the Food and Drug Administration on Friday.

That’s when the FDA shot down a petition by the Natural Resources Defense Council (NRDC) to ban bisphenol A (BPA) from food packaging. In a 15-page letter, the FDA said current research failed to prove that BPA, a compound found in the lining of canned food, water bottles, receipts and countless other products, was dangerous to human heath.  But local scientists said this is not the last word on BPA.

chemical structure for bisphenol A (BPA)

Chemical structure for bisphenol A (BPA)

“There are numerous ongoing studies that will likely yield critical new data over the next several months,” said Heather Patisaul, a professor of biology at NC State Univeristy. “That data could influence future decisions by the FDA and other regulatory agencies.”

BPA is commonly used to make polymers and resins in plastic, but it was originally developed as a synthetic estrogen. In recent years, scientists have found that BPA can mimic that hormone in the body, and have found links between BPA exposure to diabetes, aggression and infertility, prompting everyone from environmentalists to mommy bloggers to call for a ban on BPA.

In an email detailing the FDA’s decision, Doug Karas, a spokesman for the agency said, “The FDA denied the NRDC petition because it did not provide the scientific evidence needed to change current regulations.” Karas cited several studies which showed that BPA was not found in the fetuses of pregnant rodents exposed to BPA at levels 1,000 times greater than normal human exposure. Karas also noted that data shows the humans metabolize BPA quickly and efficiently.

Though the science sounds reassuring, researchers in North Carolina say it’s faulty logic for chemicals like BPA that mimic hormones, so-called endocrine disrupters. With endocrine disruptors, the old rules of toxicology regulation might not be enough to provide a clear picture of risk.

“The problem is endocrine disrupters, like BPA, can have different effects at high and low doses,” said Patisaul. “We used to think the dose makes the poison, the lower the dose the less likely to get sick, but endocrine disrupters don’t work that way, and current toxicity testing is not designed to deal with this class of compounds.”

Patisaul’s lab tries to understand how BPA influences sex-specific brain development in rodents. She’s one of the dozens of grantees funded by the the National Institute of Environmental Health Sciences (NIEHS) through $30 million of government stimulus to research BPA and its possible endocrine-disrupting effects. Her lab has shown that female rats who’ve been exposed to BPA experience accelerated puberty and infertility, while their male peers display more anxiety and aggression.

Though she said she wasn’t surprised by the FDA’s decision, she said the news shows the larger problem with our regulatory agencies.

“The BPA controversy illustrates how badly we need a more nimble risk assessment strategy for endocrine disrupting chemicals,” Patisaul said.

Rats in the Pattisaul Lab at NC State University.

Rats in the Patisaul Lab at NC State University. Part of the controversy over BPA has to do with levels of exposure in animals vs humans. Image courtesy Patisaul Lab, NCSU

Pete Myers, chief scientist and CEO of Environmental Health Sciences, said a brief lesson in regulatory toxicology illuminates the BPA/endocrine disruptor/FDA controversy: To measure the safety of a chemical, scientists experiment with a very high dose and decrease until they reach a response dose that shows no difference in reactions between the exposed and controls. They then divide that dose by about 1,000.

“That’s the reference dose considered safe,” said Myers. “But it’s never tested.” The problem is hormones and compounds that act like hormones can have very powerful effects at very low doses, exactly where the compound is considered “safe.”

Linda Birnbaum, the director of the National Institute of Environmental Health Sciences located in Research Triangle Park, said her agency knows that extremely low doses of endocrine disruptors, like dioxin, can be harmful to health. “We know that many hormones are active in the parts per trillion parts per million level,” said Birnbaum.

And, like hormones, endocrine disruptors don’t need to “build-up” in the body to have powerful effects.

“Many of our hormones have very, very short half-lives, right?” said Birnbaum. “But they’re constantly being secreted. We’re being exposed to these in a more pulsatile fashion, so you have peaks and valleys, but you have lots of exposure.”

Birnbaum said the FDA’s reading on BPA’s quick exit from the body is as example of how old toxicology thinking is being applied to endocrine disruptors. “You have these doses of BPA that pass through your body really quickly and people can say, see, it passes quickly and is cleared quickly, there’s not a lot of effect,” said Birnbaum. “But there might be long term effects of a quick pass of the chemical, how do you build models to test that?

It’s a question that Joseph Braun, a research fellow in environmental sciences at Harvard, has dealt with for years. Braun did his PhD at UNC-Chapel Hill, where some of his work focused on BPA.  Five years ago, he began following a group of Cleveland-area women in their second trimester of pregnancy.  He and his team tested their urine for BPA in the second and third trimesters, and followed their children for five years to see if prenatal BPA exposure effected childhood behavior.

“Girls born to women with higher BPA levels exhibit more behavior like hyperactivity, aggression and depression,” said Braun, who plans on following the group until their eighth birthdays.

Braun said women with higher levels of BPA in their urine were those who reported eating a lot of canned vegetables or were smokers. Women with high exposure also included those who worked as cashiers, because BPA is commonly used as the coating on thermal paper receipts. But Braun said getting an accurate picture of BPA exposure is a challenge.

“BPA exposure is really difficult to test,” said Braun. “It has a short half-life, about six hours, and is excreted in the urine very quickly.” Still, his research points to the vulnerability of the fetus to even small amounts of BPA.

Braun said the writing is on the wall for BPA, because consumer anxiety will prompt more and more manufacturers to stop using BPA in their products.

“It will be a good PR move for industry to remove it from products,” Braun said.  “The problem is, what will it be replaced with?”

John Bucher, the associate director of the National Toxicology Program, said one of the reasons his agency spends so much money on BPA is so that it can identify other types of scientific endpoints for endocrine disruptors in the future.

“We’re setting the groundwork for changing how we do things,” said Bucher.  By “we,” Bucher said he meant the field of toxicology.

NIEHS head Birnbaum said her agency’s grantees are already changing the testing paradigm for endocrine disruptors.

“Our grantees, and the FDA, are going to take the standard kind of toxicological testing paradigm and expand it by using a much broader range of doses and by looking at many other kinds of responses that are not looked at in standard toxicity testing,” said Birnbaum.

According to Myers, a new testing paradigm is desperately needed.

“How many BPA battles can we have?” asked Myers.  “It’s extremely costly to a lot of different parties, including the FDA, and its just one molecule.  We have to get past of molecule by molecule approach to testing the safety of compounds.”

And although Myers, like Braun and Patsiaul, agrees that the consumer tide has already pulled away from BPA, he said it would be a long time before the environment is BPA-free.

“BPA is cheap and it generates revenues,” said Myers. “We probably have the widest exposure through receipts. It’s very hard to go through the day without encountering BPA.”

And it may be even harder to go a day without hearing about it. The FDA emphasized that the BPA story wasn’t over, and their statements were only to be taken as  a rebuff of the NRDC’s request. The agency plans an updated safety review of BPA within the year.

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