You’re in a crowded bar near the airport and your co-worker is trying to tell you something important. She wants you to do something before you drive her car to the garage for her. She is heading out of town. But you can’t hear her over the din from the crowd. It’s too noisy, too much cross talk. Later you discover she was telling you the gas gauge is broken and the tank almost empty. But you know that. After you ran out of gas on the freeway. Now imagine you are a developing fetus. Genes in your nervous system are turning on and off in a precise sequence in response to what’s going on in your developing brain. Your neurons are growing, making new connections, responding to the cues from other parts of the system that are also developing. The signals that coordinate this involve very tiny amounts of chemicals coursing through the blood stream. Hormones, like the the estrogens. But there’s a lot of noise from artificial chemicals that also stimulate cells, but not in response to a coordinated development plan. Chemical noise from the environment.
That’s the concern about environmental endocrine disruptors. They are like the din in the crowded bar and we worry that important signals will be missed or misinterpreted or the noise will be mistaken for a message. One of the most ubiquitous of the endocrine-like noises comes from a chemical found in plastics, bisphenol-A (BPA):
It’s hard to avoid bisphenol A. One of the highest-volume chemicals in commercial production, it’s the starting material used to make polycarbonate plastics. Those are the hard, clear plastics used in baby bottles, flatware, watercooler bottles, and the work bowls of food processors. Bisphenol A (BPA) also serves as an essential ingredient of epoxy resins used to line food and beverage cans and even to seal cavity-prone teeth.
But BPA doesn’t stay put. It inevitably leaches into foods and people’s mouths, such that traces of the chemical now show up in everyone’s body. (Janet Raloff, Science News)
Scientists on two different panels of the NationalToxicology Program of the National Institute of Environmental Health Sciences have looked at the large scientific literature on BPA and come up with slightly different conclusions. One panel did not consider animal studies involving injected BPA on the grounds this was not the usual route of exposure. It bypasses metabolism by the liver. The other panel included those studies (some 200 of them, for a total of 700). The first panel was less concerned, although it did make and exception for concerns “that exposure to the chemical might perturb neural development in the womb or shortly afterward.” Quite an exception. The second panel was more alarmed, pointing to animal data associating BPA and effects that “alter rodents’ and other lab animals’ sex-specific behaviors, perturb developmentally important hormones, boost fat cell numbers and their accumulation of lipids, foster precancerous changes in cells, and induce insulin resistance, a harbinger of diabetes.” The reports of the two NTP panels will be merged and a final assessment to be issued later. Good luck.
Meanwhile more reports are coming out about BPA effects on animals at doses comparable to those to which people are exposed. The range of reported effects is broad and hard to integrate. It is likely they all reflect one or a few basic biological mechanisms, but what that might be we don’t know as yet. While it might also be true that the risk to most people is small, the ubiquity of exposure — almost everyone — is such that even rare effects can come up fairly often. Thus an effect of one in a million per year is still 300 people a year in a country with a population of 300 million. So the risk may be appreciable to the population without being particularly high for any specific individual. But there aren’t any human epidemiological data as yet.
So pretty much we don’t know about the risk to people. But the word is getting around and the market will likely be a more powerful lever than the absent government regulators. My daughter has already ditched all the plastic baby bottles for her new baby (I had nothing to do with it; she read about BPA on one of the many “mommy blogs”). She ordered glass ones through Amazon because the store was all sold out.
One of the iconic scenes in recent American film is when the young Dustin Hoffman in The Graduate is taken aside by the family friend at his graduation party for some friendly career advice: “I just have one word for you,” the friend whispers in his ear. “Plastics.”