April 29, 2008 - By Krista Conger
Bisphenol A - an estrogenlike compound in polycarbonate plastics and epoxy resin - has been popping up in the news a lot lately. On April 18, Canada announced that it would ban baby bottles containing bisphenol A beginning in mid-June. The action would make Canada the first country in the world to set exposure limits on the chemical. In addition, the U.S. National Toxicology Program, which is part of the National Institutes of Health, recently concluded that there is 'some concern' that fetuses, infants and children may be harmed by the amounts of bisphenol A that leach out of many brands of baby bottles, hard-plastic water bottles and food cans lined with epoxy resin. In the early 1990s, David Feldman, MD, and his team at the School of Medicine were the first researchers to identify and call attention to the possible impact of low levels of bisphenol A on human health. Science writer Krista Conger catches up with Feldman, an emeritus professor of endocrinology, to learn more.
1. How did you first identify bisphenol A?
Feldman: It was basically an accident; we were not looking for it. We study receptors for steroid hormones like estrogen, and wondered if they had originally evolved in yeast. Although that turned out not to be the case, we were looking for both receptors and hormones when we found what looked like an estrogenic molecule in the yeast tissue culture medium we grew the yeast in. However, the medium had been sterilized by autoclaving (a process that involves very high heat and pressure) in 'autoclavable' polycarbonate flasks. We identified the estrogenic molecule as BPA using mass spectrometry, and discovered it was present even in samples of pure water that had been autoclaved in the flasks. At that point we realized that we had identified a molecule that was leaching out of the plastic that, because of its estrogenic hormonelike properties, had the potential to be important and perhaps even dangerous to people who were eating or drinking out of containers made of this type of plastic, polycarbonate. Since polycarbonate has so many uses as a clear and strong plastic, it is ubiquitous in packaging food and beverages, and epoxy resin is used in lining metal cans.
2. What did you do next?
Feldman: We wanted to let people and governmental authorities know what we found. We sent samples to the company that made the polycarbonate flasks to warn them of the problem, but they couldn't find the bisphenol A. Our biological tests were more sensitive than the tests they were using, which were meant to identify levels of more than 25 to 50 parts per billion. Anything under that amount was considered to be safe. In contrast, we were picking up levels, and seeing estrogenic biological effects, at 5 to 10 parts per billion.
3. So, were the former regulations wrong? And why has it taken so long - nearly 15 years - to get attention?
Feldman: It's very difficult to know what 'safe' levels are. Although we published our findings in 1993, it was unclear for a long time how much of the bisphenol A was absorbed by humans, how fast it accumulated and even whether or not it was damaging to human health. In fact, to date there have been no studies showing that bisphenol A exposure affects human health. Although subsequent studies have shown that the levels to which humans are exposed do have adverse biological effects in laboratory animals, it would of course be unethical to conduct similar dosing studies in humans.
One thing we do know is that, in the 2003-04 National Health and Nutrition Survey conducted by the Centers for Disease Control, 93 percent of about 2,500 people ages 6 and above had detectable levels of bisphenol A in their urine. So almost everyone is exposed. We also know that bisphenol A is similar in chemical structure to diethylstilbestrol, a synthetic estrogen that has been linked to the development of vaginal cancer and other toxicities in the daughters of women who took the drug during the '50s and '60s to prevent miscarriage. So we know that it is possible for some of these synthetic estrogenlike compounds to have bad effects many years after initial exposure. We also need to remember that the effects of these so-called 'environmental estrogens' or 'endocrine disrupters' are additive. There are many different ways we can be exposed to these various compounds and they are cumulative.
4. Do you feel it is time for the individual consumer to take protective action?
Feldman: Well, I feel there's enough evidence to support a 'better safe than sorry' approach, particularly for fetuses, infants and children. Not only do they weigh much less than adults, making their relative exposure greater, but they are also still developing estrogen-sensitive breast and prostate tissue. In my opinion, the prudent thing for current or expectant parents or those planning a pregnancy to do would be to limit their child's exposure to bisphenol A by avoiding bottles and cups that are made of polycarbonate, and to microwave food in glass containers whenever possible. For adults, however, canned foods and beverages may be the most important source of bisphenol A.
Manufacturers are already responding to this change in consumer demand. For example, Nalgene has just announced that it will no longer make reusable drinking containers with plastic containing bisphenol A, and Wal-Mart will no longer sell baby bottles with bisphenol A. Once these major merchants begin demanding bisphenol A-free alternatives, we can hope the use of polycarbonate to package food and beverages will decline.
5. Have you changed your own habits in the lab or at home because of your bisphenol-A findings?
Feldman: Yes, to some extent. I do strongly advise my children to avoid exposing our grandchildren to bisphenol A. I don't microwave food in plastic containers, or wash the containers in the dishwasher because heat and some detergents cause leaching. I try to limit the amount of canned food I eat, or rinse the food before consuming the contents. Of course, we no longer autoclave laboratory materials in plastic. Overall, it is safest to try to be careful and avoid bisphenol A and other endocrine disrupters.
Stanford Medicine integrates research, medical education and health care at its three institutions - Stanford School of Medicine, Stanford Health Care, and Stanford Children's Health. For more information, please visit the Office of Communications website at http://mednews.stanford.edu.