Joining Tom Philpott on the anti-BPA bandwagon, the New York Times columnist Nick Kristof had an op-ed Sunday detailing the mounting evidence against the hormone disrupting chemical. One comment in particular summed up the debate nicely:

“When you have 92 percent of the American population exposed to a chemical, this is not one where you want to be wrong,” said Dr. Ted Schettler of the Science and Environmental Health Network. “Are we going to quibble over individual rodent studies, or are we going to act?”

One of the problems we face when it comes to regulating toxic substances is that the EPA and the FDA aren’t generally able to apply a strong “precautionary principle” the way regulators do in Europe. In essence, a strong precautionary principle would allow our government to act even when, as stated in a European Commission document, “scientific evidence is insufficient, inconclusive, or uncertain.” In those cases, advocates for a particular substance would need to demonstrate unequivocally the substance’s safety. Instead, we require almost total scientific consensus regarding a substance’s danger before the EPA or the FDA will act.

As a result, a great part of the scientific debate over BPA becomes “quibbles over individual rat studies” — and over the rats themselves. The best explanation of the Great Rat Debate comes from a must-read February 2009 Fast Company article about the shadowy network of so-called “product defense firms” that are used by industry to sow fear, uncertainty, and doubt over any research that questions the safety of commercial products:

The largest and most influential industry studies [of BPA] have been conducted by Rochelle Tyl of the Research Triangle Institute, a private lab in North Carolina. Tyl’s first BPA study, published in 2002 at a cost that Tyl puts at around $2 million (also funded by the Society of the Plastics Industry), examined three generations of rats and found no adverse effects at low doses. Yet here, too, there are questions of protocol. The study used a rat strain called the CD Sprague-Dawley, which has been shown to be insensitive to synthetic estrogens like BPA. (A Japanese study found that the CD Sprague-Dawley rat can withstand a dose of synthetic estrogen more than 100 times greater than what a female human can tolerate.) As of early 2007, of the 29 studies that have shown no harm due to BPA, 13 have used the CD Sprague-Dawley rat. Nonetheless, when the FDA declared BPA “safe” this fall, it relied almost exclusively on Tyl’s work — a shortcoming that the agency’s science board publicly criticized in October.

With the government’s National Institute of Environmental Health having announced a new set of BPA studies, there was concern that those same estrogen insensitive rats would be used, thus guaranteeing a “false negative” result in industry’s favor.

Rat. I recently spoke with John Bucher, associate director of the government’s National Toxicology Program, the group overseeing the research. He confirmed to me that while the new government-funded BPA studies would not use the CD Sprague-Dawley rats, they would use the NCTR Sprague-Dawley rat, derived from the CD strain back in the 1970s. While they may have similar names, they are supposedly very different rats. The CD Sprague-Dawley rat is bred and sold exclusively by the lab services company Charles River. The NCTR Sprague Dawley rat has rather been bred by the National Center for Toxicological Research for almost 40 years. Said Bucher, “we’ve used this rat for estrogenic compounds in many different studies and we are confident that it is estrogen sensitive.”

The theory goes that the CD strain is estrogen insensitive because these rats have been bred for size, since the faster the rats grow the quicker they can be sold. Meanwhile, these oversize rats are fed a soy-based feed. Soy is high in phytoestrogens (recall the ongoing debate over soy in infant formula). Such breeding practices are in the opinion of some a recipe for growing estrogen insensitive rats. The NCTR strain has not been selected in the same way (i.e. the rats display a much greater range of sizes) nor is it fed so much soy and is thus more sensitive to estrogen.

But according to Dr. Frederick vom Saal, a leader in the study of endocrine disruptors in humans, the difference between the two rat strains is minimal. He questions why the FDA has endorsed another rat study instead of one using mice, given that the rat in question appears to be “5000 times less sensitive than mice” to synthetic estrogens. Vom Saal, along with other leading scientists, recently sent a strongly worded letter — available here for the first time — to the FDA protesting this very decision [PDF] and calling on the FDA to halt the new rat trials.

But as Dr. Urvashi Rangan — director of technology policy at Consumers Union, whose recently released study of BPA in food started this latest round of media attention — observed to me, the whole issue of estrogen sensitivity in rats is beside the point.  The existing studies contain all the evidence of BPA’s danger that we need. As she put it, “you already have solid grounds to take precaution today and get it out of food substances.”

And thus are we brought back to our lack of a precautionary principle and the fact that the FDA still refuses to endorse a ban based on the existing science. And whatever uncertainties may still exist, there is one branch of government that can, if it so chooses, let the precautionary principle guide its decisions. I’m talking about Congress, of course. A majority vote is all that’s needed to ban any substance on the planet. Rather than wait for the new studies, which will take years to complete, Congress should simply act now and ban BPA on principle. The precautionary principle, that is.