A Resolution of Sorts on Bisphenol-A (BPA)

"All paid jobs absorb and degrade the mind." -- Aristotle, with thanks to the Biomes Blog, which is probably a lame excuse for why I struggle with how to blog about important but difficult-to-make-interesting-or-compelling topics such as bisphenol-A in polycarbonate plastics. There’s been plenty of handwringing about cancer, developmental health effects, obesity, etc, from BPA exposure, since the National Toxicology Program (NTP) issued its draft Brief last month (read it here if you dare). Some of the best handwringing is in these articles in Discover, including this nicely-done interview with Philip Landrigan (never heard of him? Shame on you.), who refers to environmental chemicals in general as a vast, uncontrolled human exposure study.

The NTP’s Brief on BPA says nothing new about this substance, really, but the document does that with great authority. The NTP stated, “yes”, people are being exposed to BPA. The NTP stated that BPA can possibly affect human reproduction. Effects on reproduction and development have been observed in laboratory animals at low doses that are within the range of human exposures. These include effects related to neural and behavior alterations, precancerous lesions in the prostate and mammary glands, altered prostate gland and urinary tract development, and early onset of puberty in females. The NTP says there is scientific controversy regarding the interpretation of these low dose effects, but follows with the statement, “[w] hen considered together, the results of “low” dose studies of bisphenol-A provide limited evidence for adverse effects on development in laboratory animals.”

There are a myriad of reasons for why these studies doesn’t give direct answers about bisphenol-A risks, and the NTP’s brief goes on at length, and the even longer and more complex expert report at greater length, about: whether or not adverse effects are reproducible, which is influenced by factors such as the strain of animals studied, animal care and feeding, experience of the investigator in low-dose endocrine methods and the source of funding for the study; are the results biologically plausible, a question that is embroiled in a controversy about the applicability of a dose-response relationship (the gold standard in toxicology as to whether or not exposure to a chemical causes adverse effects) to endocrine disruptors; are the observed effects really adverse effects, etc. Once again, we’ve studied the daylights out of a chemical (as with dioxin, perchlorate and TCE), and still don’t seem to have a definite answer about whether or not it poses significant health risks.

You would think that the risk management thing we need to do here seems reasonably clear. Low levels of this stuff is in the bloodstreams of nearly everyone. There are hints of evidence that similar levels tested in laboratory animals produce adverse effects, though as with all laboratory animal evidence, we don’t really know what that means for humans. The kinds of adverse effects that might be associated with exposure to BPA could extend into the next generation – if it does cause developmental behavioral effects, you might speculate about the implications of a generation of adults with behavioral and learning disabilities. We might be on our way there now, which is why initiatives such as the National Children’s Study are of critical importance.

However, as stated before, the uncertainties in the assessment of BPA don’t point directly to a decision. The easy answers (be precautionary and ban all uses; don’t be hasty, the evidence doesn’t indicate a problem) aren’t the optimal ones. At the end of the day, the most extensive risk assessment in the world isn’t going help inform a decision if the affected public isn’t going to think clearly about its values and choices; and it’s clear that we’re not good at making risk-informed decisions where uncertainty is present.

The lesson from all of this is that the debate over BPA health effects is one about values and politics, not science. It’s probably true that the precautionary principle is incoherent as a decision making tool. At the same time, inaction is a decision, and in the case of restricting BPA from food and beverage containers, one that might have long-term consequences that are severely adverse and virtually irreversible.

We seem to be groping towards a resolution, no thanks to our moribund Congress and regulatory agencies. There’s a little bit of market transparency for parents regarding BPA in plastic food and drink containers for newborns and small children. Nalgene, a major manufacturer of plastic containers is phasing out use of BPA. Though it’s expected to take several months to complete the phase out, Nalgene is, ha ha, claiming it’s products are BPA free now. I suppose it’s a victory of sorts, but I’m not going to get too excited until I see evidence that body burdens are decreasing.