[Pharmwaste] interview on "low dose makes the poison" with Dr.
Laurie.Tenace at dep.state.fl.us
Wed Sep 9 12:56:09 EDT 2009
Low Dose Makes the Poison
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
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.
Pete Myers (Courtesy of Environment Health Sciences)
They do one thing at high doses and potentially something completely
different at low doses. So if you are dependent upon high dose testing which
is the way our system works, you will never see the low dose effects. And
what that means is all of the high dose testing that we've done for decades
have been blind to this type of effect.
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
YOUNG: And this is not even in the area where the safety system is designed
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
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
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.
Interestingly, we know that people today are experiencing increasing
frequency of allergic diseases like asthma and like allergies. And now we're
seeing that one possible mechanism of it could be our exposures to
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.
Waste Reduction Section
Florida Department of Environmental Protection
2600 Blair Stone Rd., MS 4555
Tallahassee FL 32399-2400
Laurie.Tenace at dep.state.fl.us
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