Low Dose Makes the Poison
Air Date: Week of September 4, 2009
The endocrine disrupting chemical bisphenol-A, or BPA, lines many food and beverage containers, from baby bottles to canned veggies.
Modern toxicology doesn't typically test chemicals for what they do at low doses. But, sometimes, small amounts of substances can be harmful to human health, especially when it comes to the hormone-mimicking chemicals known as endocrine disruptors. Pete Myers, chief scientist of Environmental Health Sciences, talks with host Jeff Young about what tiny exposures of common chemicals do in our body, and why regulatory agencies don't test low doses
CURWOOD: It’s Living on Earth. I’m Steve Curwood.
YOUNG: And I’m Jeff Young.
When toxicologists test a chemical’s safety they typically use high doses to find health problems. But that approach has missed the potential dangers of some substances that can be hazardous in tiny amounts. They’re known as endocrine disruptors because they mimic or block hormones. Some, like bisphenol A, and phthalates, are common ingredients in plastics and other consumer items.
Recently, the Government’s National Institute of Environmental Health Sciences published a paper challenging regulators to change chemical safety tests to reflect this emerging scientific understanding about low doses. Dr. J. Peterson Myers is the lead author.
MYERS: Our regulatory safety net, the FDA or the EPA, the all depend upon a core assumption – that when they test at high doses those tests will reveal what’s happening at low doses. The problem is that when you’re dealing with contaminants that behave like hormones, it doesn’t work that way.
YOUNG: Why is it that these chemicals can start to show problems at low doses instead of at high doses?
MYERS: What hormones and these contaminants do is at very low doses they turn on and off genes. Genes are being turned on and off trillions of times a second throughout your lifetime. And the orchestration of that is absolutely vital to life. If the genes get turned on or off at the wrong time, that’s gonna lead to a problem. You’re gonna lack a protein that might be important for example in suppressing a tumor or in controlling the growth of your heart. And the body’s control system for these genes is designed to function at really, really low levels.
YOUNG: How low are we talking about?
MYERS: We’re talking parts per trillion to parts per billion to low parts per million.
YOUNG: And this is not even in the area where the safety system is designed to look.
MYERS: The safety system is not designed to look there. It starts at parts per thousand and rarely gets to low parts per million and never gets to parts per billion.
YOUNG: So we’ve all heard the phrase “the dose is the poison.” And that really is the assumption that a lot of toxicology is working on.
MYERS: It’s an assumption that’s been around since the 16th century. It was based upon work by a guy named Paracelsus in Switzerland. And the way the tests work today is we think that by testing at high doses we’re gonna see everything. So that once we get to a dose that’s intermediate and we don’t see anything, we’re golden.
But the science is telling us that at really low doses as contaminants mimic hormones. They can have effects that are totally unpredictable by what happens at high doses. And now we’re watching as toxicology is overturned by new science from endocrinology. Endocrinology is the study of hormones and its only because endocrinologists brought their skills and knowledge into this field and began asking these new questions that we began seeing the results like this beginning about a dozen years ago.
YOUNG: So it’s emerging science, but it’s not brand spanking new. Why haven’t we been looking for this sort of response when we’re trying to determine whether or not a substance is safe?
MYERS: I should emphasize that it’s not even close to brand spanking new. It’s solid in endocrinology. This is something that physicians have to structure their drug deliveries around. They know that at low doses you can cause effects that don’t happen at high doses. In fact, you can cause the opposite effect.
And the best example of that is a compound called Tamoxifen that’s used by physicians to cure breast cancer. It works at high doses to suppress the growth of the breast cancer tumor. That’s exactly what you want it to do. But at a level about a million fold beneath that toxic dose, it turns on genes that are responsive to estrogens and causes to breast tumor to grow. And if you only to the classic experiments of high doses until you don’t find and effect, you miss this.
YOUNG: And are we beginning to see that that’s happening, that the findings from endocrinology are indeed being put to work in our safety system?
MYERS: Well, not yet. There’s a battle underway today over bispenol A. The low dose experiments say it’s risky and we shouldn’t be using it with food products. But to date the agency reviews of bisphenol A have basically depended upon traditional high dose experiments by contract laboratories, and have not been willing to pay attention to the low dose studies published by academic scientists doing this new research.
Another endocrine disrupting compound that has been shown to have these different effects at low doses than at high doses are some of the phthalates, a common plasticizer added to plastic to make it pliable and soft. This fascinating work showing that at really low doses phthalates alter our responsiveness to allergens. They make us hyper allergic. So the standard tests that are used to assess toxicity don’t even begin to tell you about this effect of phthalates.
YOUNG: So maybe that gives us some insight into why the bisphenol A issue is so hard fought. It’s about more than just BPA.
MYERS: It is about more than just BPA. BPA itself is a big deal. You do the calculation and it’s worth about $800,000 an hour. You can buy a lot of lawyers to defend your product with $800,000 an hour in revenue. But BPA is the poster child of this low dose debate. And if BPA is regulated based on low dose effects, it explicitly acknowledges that the regulatory system has been blind to these types of effects. And BPA is not the only one that’s gonna have to be re-examined.
YOUNG: Now EPA has been taking some steps in this direction. Give me an assessment of what the environmental protection agency’s been doing in terms of these endocrine disrupting chemicals?
MYERS: Very little. There’s a program that’s been underway mandated by the Food Quality Protection Act of 1996 that instructed the EPA to develop testing and screening criteria for endocrine disrupting compounds. And just this past year, it identified candidates to measure. Congress actually expected them to be measuring these things within a few years and here we are 13 years after the passage of that act and EPA has just identified what candidates they should look at. And it’s a small incomplete list.
YOUNG: That's Dr. Pete Myers, CEO and chief scientist of the non-profit Environmental Health Sciences – that paper on endocrine disrupting chemicals is at our website, loe.org.
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