Science & Technology: BIOLOGY
IS YOUR REPRODUCTIVE SYSTEM IN DANGER?
The U.S. plans a controversial test of some 87,000 compounds
In September, the Environmental Protection Agency will start seeking public reaction to one of the largest environmental testing programs ever. Under congressional mandate, the agency proposes to screen some 87,000 compounds over the next two years, at a cost to the chemical industry of more than $100 million. It's all aimed at settling a scientific debate stirred up two years ago when some researchers argued that widely used chemicals might be having disastrous effects on the reproductive systems of both humans and animals.
But scientists are far from unanimous about the damage these chemicals might cause. Indeed, the most recent evidence suggests that the problem has been overstated. Granted, worrisome reports have continued to appear (table, page 108). Earlier this year, researchers reported that the ratio of male births to females in some groups is dropping. Girls were found to be reaching puberty much earlier. The incidence of male genital birth defects is rising, and rates of breast and testicular cancer are soaring. The most heated debate centers on a controversial set of data that may or not indicate that male sperm counts are declining worldwide; the latest analysis says they are.
While some researchers believe these findings are the result of exposure to at least a few of the chemicals the EPA is about to begin testing, others take a far more cautious position, arguing that the evidence is still highly uncertain. And new studies reported at the meeting of the American Chemical Society in August did little to resolve the debate.
Researchers reported finding a sharp decline in the amphibian population in areas of the Sierra Nevadas with heavy concentrations of pesticides. They found an increased incidence of non-Hodgkin's lymphoma in women with high levels of exposure to polychlorinated biphenyls (PCBs), a now-banned chemical used in insulation. On the other side, however, researchers said that no link was found between breast cancer and PCB exposure. Nor could the Food and Drug Administration find evidence to support the theory that some chemicals were seeping from packaging into food.
The EPA's daunting task is to settle the issue--despite the fact that scientists have yet to agree on the best ways to test for these chemicals. "This is a very controversial issue at the cutting edge of science, and the EPA is right in the middle," acknowledges Gary E. Timm, a senior technical adviser to the agency's chemical division.HUGE UNDERTAKING. The cause of all this concern is a class of synthetic chemicals referred to as endocrine disruptors. They are suspected of doing damage by chemically mimicking hormones and interfering with the endocrine system, which controls reproduction and other bodily processes. The compounds range from such widely recognized chemicals as DDT and PCBs, banned in the U.S. and Europe, to chemicals used in virtually every plastic container and detergent (table). Similar hormone-mimicking chemicals also occur naturally in whole grains, soybeans and many fruits and vegetables, part of the reason that some critics say the concern is overblown. If the synthetic chemicals are guilty as charged, it would be a huge undertaking to phase them out; most have become part of the very fabric of modern life.
Scientists have been studying potential endocrine disruptors in earnest for the past decade. But the issue was blown into the public eye by the 1996 book Our Stolen Future, written by Theo Colborn, a biologist with the World Wildlife Fund, and two co-authors. The authors gathered a wealth of data on birth defects, sexual abnormalities, and reproductive failures and blamed the problems on chemical exposures. The book, with a foreword by Vice-President Al Gore, set off a public and congressional debate that led to the law requiring the EPA testing program.
But several of the studies cited in the book turned out to be seriously flawed. The most controversial, first published by Danish researchers in 1992, concluded that male sperm counts had fallen throughout the industrialized world from 1938 to 1990. The study was based on a review of 61 scientific papers from around the world, covering nearly 15,000 men. When other researchers reanalyzed the data, using different statistical measures, they found no decline. The latest reanalysis, published late last year in the journal Environmental Health Perspectives, used several mathematical formulas aimed at determining regional differences and backed up the original conclusion--that "strong and significant sperm density declines were seen overall in the United States and Europe but not in non-Western countries." The researchers, from the California Health Services Dept., did find large intraregional differences. But their study did not look for a cause, and further studies are needed to determine whether endocrine disruptors are responsible.
Science is still a long way from making such a determination. Chemists admit to being mystified as to why certain chemicals appear to interact with the endocrine system, and there is no surefire way to screen for them. Also to be determined is whether these chemicals affect humans and animals differently, the amount of exposure required before a chemical becomes dangerous, and the effect on fetuses. "The science is moving very, very slowly," says Timothy P. McNeal, a senior researcher with the FDA. "We still don't have good, definitive data, so interpretation is difficult."FALSE POSITIVES? Even so, the EPA has no choice but to forge ahead. The Food Quality Protection Act of 1996 requires it to screen all chemicals found in food and drinking water for endocrine disruptors. The EPA plans to start this year by sorting through some 87,000 chemicals in common use, narrowing them down to 15,000 that are the most likely to disrupt the endocrine system. By the end of 1999, the agency plans to test all 15,000--at a cost to the manufacturers of about $200,000 per chemical--to see which are most likely to interfere with hormones. Then comes a third round of tests on the strongest suspects, looking at their impact on lab animals, at a cost of about $2 million each.
Chemical industry advocates are already on the offensive. Christopher J. Borgert, president of the Florida-based consulting firm Applied Pharmacology & Toxicology, says the EPA's screening tests are likely to be unreliable--and will create a lot of false positives. "This is clearly a situation where the policy and politics got way ahead of the science," complains environmental lawyer Terry F. Quill of the Washington law firm Beveridge & Diamond.
But plenty of scientists argue that the potential dangers are too worrisome to wait. "Look how long it took to agree on global warming," says Dr. Ana M. Soto of Tufts University School of Medicine, who started studying endocrine disruptors in 1989 after chemicals contained in plastic test tubes spoiled her estrogen experiments. "On this we cannot wait until the data is here," says Soto. "I'm speaking as a citizen, not a scientist."
Scientists, though, tend to be cautious. John Brock, a biologist with the Centers for Disease Control, says he knows firsthand the dangers of a rush to judgment. To his surprise, he recently found a fivefold increase in non-Hodgkin's lymphoma among women exposed to high levels of PCBs, but no strong association between PCBs and breast cancer. "Although I'm very concerned about these chemicals, we have to be very cautious in how we proceed," Brock says. But even he feels the EPA must move ahead with its testing plan. "We're doing this for our children and our children's children." Which could be worth a lot more than $100 million.By Catherine Arnst in BostonReturn to top