BPA

BPA, short for bisphenol A (and yes, bisphenols B and C do exist as well as a plethora of others) is a regular topic in the news. The New York Times had an article last week summarizing some of the work at attempting to determine the safety of the chemical at the levels that people are being exposed to it. The article's title "In Feast of Data on BPA Plastic, No Final Answer" should give you an idea of the discussion.

Modern Plastics, September 2010, p. 12 (available online) has two perspectives, one from Dr. David Feldman who first discovered that BPA had estrogen-like interactions on yeasts, and one from Steven Hentges of American Chemical Council.

Dr. Feldman's arguments are not convincing. His central argument is that DES, diethylstilbestrol (shown below) is structurally similar to BPA, and that when DES was used as a drug to prevent miscarriages, 20-30 years later the girls were later found to have an unusually high rate of vaginal cancers.

The structural similarity is easily seen although certainly there are plenty of examples that medicinal chemists can provide of structurally similar chemicals having wildly different properties in the body, but I think an even stronger argument is that the exposure to the DES was so much higher than any exposure to BPA. The dosing levels were in the 5 to 25 mg range, perfectly appropriate for a drug, but not anywhere the exposure levels that people can incidentally pick up from PC bottles. These exposure levels are in the microgram or submicrogram range.

Additionally, Dr. Feldman states that the binding strength at the estrogen receptor site is 1000 to 2000 times less than estradiol, which at least partially explains why DES has to be dosed at such high levels compared to the levels of hormones in the body.

I'm not sure that Dr. Feldman was the best person to provide this perspective on the potential hazards. By his own admission he is no longer an active researcher in the field, having moved on to other areas. And I certainly can understand that he may well have additional support for his position that editorial constraints did not allow space for. I still would recommend the Modern Plastics article however, as there is no shrill fearmongering to be found anywhere in it.

(All pictures courtesy of Wikipedia.)