NPR on precautionary principle.
NPR's exploration of the precautionary principal hits the right notes but gets a few key scientific details wrong.
Pegging a story around a quote from Senator Dianne Feinstein on why the precautionary principle justifies a ban of bisphenol A, NPR's Jon Hamilton interviews two scientists, Dr. Ted Schettler and Dr. Linda Birnbaum. They provide a more nuanced and substantive view of what the precautionary principle involves than the Senator's quick description. It's a good treatment of a complicated issue that is likely to become a common theme as Congress contemplates revising the decades-old laws used to regulate toxic chemicals.
Where Hamilton falls short is in two details of his summary of bisphenol A science:
He states: "BPA can act like a weak form of estrogen." This is based on outdated science which assumed that BPA and estrogen acted only through one specific mechanism, binding with an estrogen receptor in the nucleus of a cell. Via this mechanism, BPA appeared to be much weaker than the main human estrogen molecule, estradiol.
In the last several years research has revealed that both estradiol and BPA can also act through another mechanism, not within the cell's nucleus but instead on the cell's surface membrane. Acting through this mechanism, BPA is just as powerful as estradiol. And both are capable of provoking cellular responses at extremely low levels, less than one part per trillion. This pathway of action is linked to BPA's (and estrogen's) potential roles in disrupting insulin metabolism. Hence to continue to characterize BPA as a weak estrogen is out-of-date. It can be a powerful estrogen.
Hamilton's second mistake is in his characterization of levels of BPA used in animal experiments. He states: "high doses of BPA can cause reproductive abnormalities and cancer in animals." Actually, many studies using very low doses of BPA, doses that lead to blood concentrations in animals well below the levels common in people, are sufficient to cause a wide array of adverse effects in animals. This is summarized in a series of review articles and consensus statement emanating from a meeting of experts on BPA convened by the National Institute of Environmental Health Sciences and the EPA.
It doesn't take high doses of BPA to cause harm in animals. Very low doses suffice. That's one of the key differences between research on BPA and that conducted on most other contaminants. Many studies have been carried out using BPA exposures that are well within the range of what people experience. Correcting that misrepresentation casts a different light on the appropriateness of using the precautionary principle with BPA.
