The Dose Doesn’t Always Make the Poison
Many tin cans are lined with Bisphenol A, an endocrine disruptor. (Photo: Flickr Creative Commons, Aerrin99)
Many common household products contain chemicals that could be hazardous to human health. Now, a new report finds that for some chemicals, a very small dose can have a very large health effect. Host Bruce Gellerman talks to Laura Vandenberg, a researcher at Tufts University Center for Regenerative and Developmental Biology, about how exposure to small amounts of chemicals can act like hormones and have adverse health effects on humans.
GELLERMAN: From the Jennifer and Ted Stanley Studios in Somerville Massachusetts, it's Living on Earth. I'm Bruce Gellerman. Generations know Campbell's soup as comfort food:
[MUSIC OF CAMPBELL'S SOUP COMMERCIAL: "soup and sandwich go together....m'm, m'm good! Campbell's of course."]
GELLERMAN: But for months consumer advocates have complained that Campbell's is bad for you, not the soup but the can. They charge the chemical Bisphenol A, used to line soup cans, can mimic human hormones, and they cite studies linking BPA to hyperactivity, obesity and depression in kids, and heart disease and diabetes in adults.
To address those concerns, Campbell's has announced it's phasing out the use of the chemical in its cans, and the FDA, which has maintained BPA is safe at low levels, is reviewing the scientific evidence, and will announce its findings at the end of this month.
But BPA is just one of the many chemicals found in thousands of common products that scientists suspect can act like hormones. A new study, which reviews hundreds of research reports into these so-called endocrine-disrupting chemicals, is just out. The lead author is Laura Vandenberg, a developmental biologist at Tufts University.
VANDENBERG: The way that traditional toxicologists look at chemicals is they look at: does this chemical kill, or does this chemical prevent pregnancy completely. It doesn't address - does this chemical change the subtle organization of the brain? So we found chemicals that are working at that really low level, can take a brain that's in a girl animal and make it look like a brain from a boy animal, so, really subtle changes that have really important effects.
GELLERMAN: So it goes against the notion of 'the dose makes the poison.'
VANDENBERG: Exactly. So, when the dose makes the poison, the more of it that you're exposed to, the more toxic it is. In this case, very, very small doses act like hormones, and that's why they have effects at low doses.
GELLERMAN: So how small an amount are we talking about here?
VANDENBERG: We're talking about chemicals that can act in the part-per-billion or part-per-trillion level. So part-per-trillion would be 1/20 of a drop of water in an Olympic-sized swimming pool.
GELLERMAN: Or one drop in 20 swimming pools!
GELLERMAN: And these chemicals are in things that we're exposed to everyday?
VANDENBERG: Absolutely. So these are chemicals that are in our food and food packaging, they're in the things that we use to clean our bodies and our homes, they're in things that we spray on our lawns. So these are chemicals that are used for a very particular purpose, but they have adverse effects.
GELLERMAN: So, you mentioned lawn-care products, pesticides, detergents, cosmetics, what should the consumer look for?
VANDENBERG: It's very difficult. So, a lot of consumers think: How do I shop my way out of this problem? how do I avoid these chemicals in the grocery store? And the real problem is - we can't shop our way out of this problem. The real question is - can we buy products that don't contain hormonally active chemicals?
GELLERMAN: But if it doesn't say it on the labels...
VANDENBERG: That's exactly the problem. I would say that I'm fairly educated on this topic, but I'm not a chemist. And when I go to the store, I have no idea whether a product contains a hormone mimic.
GELLERMAN: What about the chemical BPA, Bisphenol-A. It was used in plastic, it was used to coat cans in the supermarket...
VANDENBERG: What we find is that there's overwhelming evidence in animals that BPA is associated with drastic changes in mammary gland development, also changes in the induction of mammary cancers, and changes in the sensitivity of the animal to carcinogens. So it makes you more sensitive to a carcinogen.
GELLERMAN: Well, there's a chemical called tamoxifen, people know it because it's used to treat breast cancer.
VANDENBERG: That's correct.
GELLERMAN: That has been suspected to have an estrogenic effect at very low doses, and that is suspected to be one of these chemicals that you're referring to.
VANDENBERG: So, tamoxifen is taken by women who have breast cancer, so it's a pharmaceutical. The idea is that women who take tamoxifen have to go through a period when it's building up inside their bodies. So, the first few weeks of when they start taking it at a low dose, it will actually cause their breast tumors to grow, so it's actually dangerous at low doses, until the amount in their body gets to a high level and it will kill those tumors. So for women who are taking tamoxifen, they normally go through a period of time that's quite uncomfortable for them, it's called tamoxifen flare. And during that period of time, their cancer is actually progressing before it can get to the point where that tamoxifen will start killing their cancer cells.
GELLERMAN: Your study was a meta-study, it was a study of studies.
VANDENBERG: That's right, this current study looks at lots and lots of chemicals.
GELLERMAN: So you looked at them at the animal level...
VANDENBERG: That's right.
GELLERMAN: The human level...
VANDENBERG: That's right.
GELLERMAN: ...and, the cellular level.
VANDENBERG: That's exactly right. Yeah, we were really trying to say - if we look at these chemicals as a whole - what can we learn from them? Do they have actions that are very specific to a chemical, so, is BPA special in some way, or is BPA representative of what a lot of these chemicals would do and act like?
GELLERMAN: What's the reaction you've gotten from industry, the chemical makers?
VANDENBERG: For years, the industry has argued that chemicals don't have an effect at these low doses. But now we have this huge body of evidence, all of these papers looking at hundreds of chemicals, and we're asking them now to reconsider that position; that, perhaps, chemicals are not safe at low doses.
GELLERMAN: So what does a regulatory agency like the FDA or the EPA, what are they left to do?
VANDENBERG: The way that regulatory science generally approaches chemical safety is by giving an animal a huge amount of a chemical, seeing how many animals die because of that huge amount of chemical, and then calculating what would be a "safe" amount of that chemical, but the safe amount is never actually tested. What we're asking them to do is to actually test chemicals at the dose that is suggested to be safe. It seems like a no-brainer, and yet it's not the way that chemical testing is currently done.
GELLERMAN: So, for the layperson, the take away message from your study is...
VANDENBERG: That chemicals that act like hormones are not safe at the doses that we're exposed to. There is no safe dose of a chemical that mimics a hormone.
GELLERMAN: Well, Dr. Vandenberg, thank you so much for coming in.
VANDENBERG: Thank you so much, it's been great!
GELLERMAN: Laura Vandenberg is a research fellow at the Tufts University Center for Regenerative and Developmental Biology. For more on her study, head to our website, loe dot org.
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