Monday, October 15, 2007

Polycarbonate plastics: if only toxicology could be that clear

An ongoing debate about the health impacts of bisphenol A (BPA), the ubiquitous chemical used in production of polycarbonate - that hard clear plastic we use for eating, drinking, and storing food – continues, according to a recent article by Janet Raloff published in the September 29 issue of Science News. Her analysis provides good insight into why we often hear conflicting reports when it comes to environmental and health impacts of chemicals.

Raloff reports on the conflicting results of two different panels recruited by the National Toxicology Program (NTP) and charged with reviewing and evaluating the potential developmental and reproductive impacts of BPA. While one panel “labeled ‘as confident’ its assessment that BPA at low doses has had negative effects on experimental animals,” and that such findings were suggestive of impacts in humans, the other panel “concluded that current BPA exposures appear to pose little risk to humans.”

According to Raloff, one of the differences cited in this analysis, leading to conclusions ranging from don’t use the stuff if you don’t have to, to it’s a non-issue, were concerns about the basic experimental design used by scientists evaluating BPA. When laboratory animals are exposed to experimental chemicals there is often a trade-off between ensuring exposure to the chemical, verses exposing the animal in a realistic manner. Way back when, when I was interested in the effects of PCBs in fish populations, I’d load up syringe and inject. Now unless fish were mainlining PCBs (and concentrations in some wild fish were certainly suggestive of that!) clearly this wasn’t realistic. But, what it did provide us with was an exposure where we were sure that PCBs got to where we wanted them to go. Confident of our exposures (we’d also do some chemical analysis – which was the most costly part of the study back then, and so something toxicologists would like to avoid if at all possible), we could more efficiently get down to our intended business, evaluating the effects. Our option would have been to develop food with amounts of PCBs that fish would eat in amounts that we could somehow measure (you ever watch fish eat? Biting off pieces of food, letting the rest drift to the bottom, possibly snatched up by less aggressive fishes), that wouldn’t leave us with gallons of toxic water to cleanse in the end. The fact is there are often good reasons to use the needle, although as pointed out by the panels, there are limitations to these kinds of unrealistic exposures, one of them is interpreting experimental results to a broader range of more realistic exposure scenarios.

Raloff outlines other differences in the panels, for example, she writes that the panel which concluded impacts are likely, had either worked with the chemical or similar chemicals, while the panel that came to nearly an opposite conclusion “were selected precisely because they had no direct BPA experience and, therefore, no obvious vested interest in judging the quality of the data on the chemical.” Fair enough, I suppose. You’d hope scientists can see past their own interests, although I’ve always thought it’d be interesting to see a study correlating the evaluation of experimental data with sustained funding for a particular subject over a period of time.

For more details on the subject, the article is available on the Science News site, and, according to Raloff, “ultimately, NTP will issue a single report that integrates conclusions from both panels, along with any new information on BPA that comes to light during the next few months.” Now that ought to be an interesting read.


Dori Digenti said...

Hi, friend,

I just started a new website at AND just linked to, you've done a lot of work here -- can't wait to read...

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