Air Date: Week of October 20, 1995
Science and medical reporter David Baron of member station WBUR examines the latest scientific findings on chemicals that disrupt human and animal hormone systems. Recent discoveries by government scientists point to a blocking of the bodies androgens; a key breakthrough in scientific understanding of this health puzzle.
CURWOOD: This is Living on Earth. I'm Steve Curwood. For years, the big human health concern about such environmental toxins as pesticides, PCBs, and dioxins, has been their power to cause cancer. But increasingly, scientists are becoming worried that these chemicals, many of which contain chlorine, are disrupting animal and human hormone systems. This can lead to major problems in the areas of brain function, immune systems, and the ability to reproduce. The trouble is, science couldn't say exactly how they work in the body. For example, much evidence suggests that some of these chlorinated compounds can mimic the female hormone estrogen. Yet they don't look chemically much like estrogen. Now government scientists believe they have figured out how some of these chemicals interfere with reproductive function. David Baron of member station WBUR reports.
BARON: Scientists have compiled a long list of compounds that can disrupt the hormonal or endocrine systems of laboratory animals, and may be responsible for health effects in wildlife and even people. These chemicals, called endocrine disrupters, include components of plastic, industrial pollutants such as PCBs, dioxins and furans, and pesticides such as DDT, methoxychlor, and endosulfan. Researchers have been particularly concerned about chemicals that appear to interact with reproductive hormones. Even at low doses, some of these chemicals can trigger the development of feminine traits in male animal embryos in the laboratory. And these substances have been blamed for disrupting sexual development in wild populations of fish, birds, and other animals. Some scientists suspect the chemicals might also be responsible for human reproductive problems in the offspring of women exposed to the compounds, perhaps causing reported increases in the rate of undescended testes in baby boys and testicular cancer in men, as well as in apparent decline in sperm counts. Because some of these chemicals mimic the female hormone estrogen, they've been dubbed environmental estrogens. Research into these chemicals is at a very early stage, and there's a great deal of uncertainty over what impact they have on human health. There have also been big questions about exactly how they do their damage.
GRAY: It was clear that many of the chemicals that had endocrine-like effects were not estrogens, and so it's been sort of puzzling.
BARON: Toxicologist Earl Gray believes he and his colleagues have now solved part of that puzzle. Gray, who studies endocrine disrupters at the US Environmental Protection Agency's Health Effects Research Laboratory in North Carolina, has taken a new look at chemicals that seem to have feminizing effects.
GRAY: There's no question that focusing just on estrogens is too simplistic.
BARON: Hormones such as estrogen are chemical messengers that work by binding with receptors in cells, like a key fitting into a lock. If a hormone or a chemical that mimics a hormone successfully opens that lock, it can trigger a host of changes in the body. Estrogen, for instance, causes the development of breasts and controls menstrual periods. But Gray points out some chemicals can latch onto hormone receptors without triggering a response, but still causing problems in the cell.
GRAY: It's like sticking the wrong key in the lock and jamming the lock. So the lock and key mechanism is now occupied and stuck. But you can't get the door open.
BARON: So here's what Gray and his colleagues speculated. Perhaps some of the problems in humans and wildlife attributed to estrogen-like compounds in the environment are really due to chemicals blocking male hormones, such as testosterone. These chemicals are called anti-androgens.
GRAY: And no one was aware that environmental anti-androgens existed.
BARON: Gray and his colleagues have now shown conclusively that they do exist. They found 20 anti-androgens so far, and one of the most potent is a common pollutant. DDE is a breakdown product of the pesticide DDT. While DDT was banned in the United States more than 20 years ago, it continues to be used in many developing nations. DDE is found in the environment around the world and accumulates in the human body. The EPA scientists reported recently that DDE blocks the androgen receptor of both rats and humans . Male rats exposed to DDE as embryos developed nipples, which male rats normally don't have, as well as feminized genitals. This discovery has caused scientists to reexamine their old observations in a new light. University of Florida zoologist Lou Guillette has been studying deformed alligators in Lake Apopka, a large body of water in central Florida contaminated with DDE and other chemicals. Guillette had originally attributed the deformities in the animals to pollutants acting as estrogens.
GUILLETTE: But things bothered me, and that was is that one of the other things that we began to notice was that many of the males had abnormally small penises, and we know that penis development is testosterone dependent. That is, having elevated levels of estrogen probably wouldn't cause that effect. But they fit perfectly well under a scenario of depressed androgen because of an anti-androgen present.
BARON: Scientists like Guillette now suspect many of the effects they had attributed to the feminizing influence of environmental estrogens might really be due to the demasculinizing influence of anti-androgens. This seemingly subtle distinction represents a major change in thinking, say scientists. Even skeptics of claims that endocrine disrupters pose a major threat to people, such as toxicologist Steven Safe of Texas A&M University, consider the new EPA findings important.
SAFE: This paper is significant in that it opens up a whole new area that people didn't know existed before.
BARON: Safe cautions it's still too soon to conclude that endocrine disrupters are harming people, but he encourages further study. University of Missouri biologist Fred Vom Saal adds that the discovery of anti-androgens suggests scientists should look more broadly at many hormone systems that might be disrupted by pollutants.
VOM SAAL: For instance, the hormone progesterone, the adrenal hormones. We don't know whether these chemicals can also interfere with other hormone systems because nobody was really looking at anything except for the possibility of them acting like estrogen.
BARON: Vom Saal argues many chemicals that had been ruled out as endocrine disrupters because they had no apparent estrogenic effect must now be reconsidered. The EPA is hoping to boost funding for research into endocrine disrupters with new grants slated to be given next year, but scientists aren't banking on that money. If Congressional Republicans succeed in their efforts to cut a billion dollars or more from the EPA's budget, researchers fear it could be a long time before they're able to determine if environmental estrogens, anti-androgens, and other endocrine disrupters are harming human health. For Living on Earth, I'm David Baron reporting.
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