The Food and Drug Administration has quietly delayed a reassessment of the chemical BPA. BPA is a widely used additive. It's found in plastic bottles and food containers and it can mimic the hormone estrogen. Concerns have been raised recently about BPA's safety. FDA officials had promised an announcement by the end of November.

NPR's John Hamilton explains what's going on.

JOHN HAMILTON: Earlier this year, the FDA seemed poised to change its stance on BPA. Many food and beverage containers are made with the chemical. In June, the FDA's new chief, Margaret Hamburg, promised the agency would reconsider its position that BPA is safe.

And in August, the FDA science advisory board held a public hearing on BPA. It included testimony from a lot of people who think the chemical is not safe. Among them, Ellie Collinson of the Breast Cancer Fund.

ELLIE COLLINSON: The science is clear and the time has come to remove this toxic substance from our food supply.

HAMILTON: Jennifer Sass of the Natural Resources Defense Council.

JENNIFER SASS: FDA should list BPA as a substance prohibited from the use in human food.

HAMILTON: Olga Naidenko of the Environmental Working Group.

OLGA NAIDENKO: We feel that for BPA, they don't know enough to take action right now.

HAMILTON: And Elizabeth Hitchcock of the U.S. Public Interest Research Group.

ELIZABETH HITCHCOCK: The federal government should regulate this and other toxic chemicals to protect our children's health.

HAMILTON: The FDA was feeling a lot of pressure. Then in October, the National Institutes of Health announced that it would spend $30 million on a whole new round of BPA studies. Moreover, the new studies would address some perceived shortcomings in previous research. Since then, the FDA has gone silent on BPA. Its self-imposed November deadline came and went, and the agency has declined to offer an explanation or a new deadline.

Sarah Vogel of the Johnson Family Foundation says the prospect of lots of new BPA studies puts the FDA in an awkward position.

SARAH VOGEL: How do you make a decision when you want to have, of course, all the information in front of you? You also want to be health protective. You know this research is coming, but some of it is not going to be done for quite a while. So, you know, I think that's probably a difficult issue that FDA is having to weigh.

HAMILTON: Vogel is one of several dozen scientists who sent a strongly worded letter to the FDA this fall urging it act without waiting for more research. The authors of that letter include many academic researchers who have done studies on BPA. And many of those studies suggest BPA can cause problems like abnormal sexual development, at least in animals.

But Vogel says academic scientists generally haven't conducted the sort of studies that government agencies use to assess risk.

VOGEL: You have a scientific community that's asking hypothesis-driven questions. They're not thinking about setting a regulatory safety standard.

HAMILTON: That's made it hard for regulators to draw conclusions from these studies.

Wolfgang Dekant is a toxicologist at the University of Wurzburg in Germany. He was on a panel that reviewed BPA research a few years ago for the European Food Safety Authority. Dekant says the panel looked for studies that met certain criteria.

WOLFGANG DEKANT: For example, your study has to be reproducible. Your effects have to be consistent. Your statistics have to be correct. You have to use larger group sizes.

HAMILTON: Dekant says many of the studies just didn't measure up.

DEKANT: In addition, a number of other studies we have tried to repeat or replicate the effect of low dose studies, and who were usually statistically more powerful, have not been able to reproduce this data.

HAMILTON: Meanwhile, the larger studies, often paid for by industry, found no risk from BPA, even with exposures hundreds of times higher than most people get. So the European Union decided to do nothing.

In the U.S., regulators have been frustrated by another feature of these academic studies. Earl Gray, a scientist with the Environmental Protection Agency, says most academic researchers haven't used oral doses in their experiments. Instead, he says, they inject animals with BPA, also known as bisphenol A.

EARL GRAY: Bisphenol A when it's injected, bypasses a lot of the liver's metabolism and so you can see effects that you can't get with oral administration.

HAMILTON: That's why regulators, like the FDA, prefer studies in which animals are exposed to BPA the same way people are, by mouth. The new NIH-funded research should provide more of those studies and that would make a decision about BPA's safety easier.

John Hamilton, NPR News.

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