Inquiry Turns To Humans On Pollutant, Hormone Tie

· Bisphenol A, used as a building block for hard plastic goods like bottles and as a resin to line food cans, has been connected in some experiments to abnormal sexual development in male lab rodents, as well as a predilection for obesity. Officials from the chemical and pesticide industries have vigorously criticized these results, saying that other studies have shown the chemical to be harmless.

· Treated sewage, which carries human estrogen and birth-control pill components excreted in waste, has been linked to "feminized" male fish in waters around the world. In the St. Lawrence River in Canada, a recent study found that a third of male minnows had female characteristics. Another example might be the Potomac, though the cause of its problems has not been officially pinpointed. The EPA and sewage-plant officials have said they are working on ways to better clean the wastewater.

The study of endocrine disruptors began in the late 1980s and early 1990s, with scientists struggling to add up such oddities as male birds with female organs in the Great Lakes and sexual defects in Florida alligators.

They eventually found that some chemicals were turning on hormone switches in the body's endocrine system that trigger biological processes. Others blocked the switches so natural hormones couldn't get through.

That revelation meant that a pollutant could be harmful even if it wasn't poisonous and didn't cause cancer. Even small doses could cause major damage, if they came at a key time when hormones were guiding pregnancy or early development.

"We have to ask different questions," said John Peterson Myers, an activist and former scientist based in Charlottesville. He joined with scientist Theo Colborn and writer Dianne Dumanoski to write a book laying out their concerns, 1996's "Our Stolen Future."

Today, despite the wealth of studies in animals, the implications for human health are unclear. One of the most dramatic studies examined the sons of mothers whose bodies contained phthalates. It found no major birth defects but did show that the higher the phthalate level, the greater chance that the boys' bodies would show subtle signs of being "undermasculinized," according to researcher Shanna Swan, director of the Center for Reproductive Epidemiology at the University of Rochester.

Still, that falls well short of a smoking gun: Humans are not laboratory rats, so scientists say it is exceedingly hard to craft a study that shows a particular chemical caused a particular problem, and not genetics, diet or some other factor.

"They're nowhere near cause-and-effect," L. Earl Gray Jr., a senior research biologist at the EPA, said of human studies. "We're showing correlations and associations" between pollutants and human health effects, he said, but no indisputable sign that one causes the other.

Officials from the chemical and pesticide industries have vigorously defended their products, saying they see no reason for concern about products in the environment interfering with human hormones.

Some scientists have also pointed out that human diets have always included some estrogen-like compounds: They occur naturally in wine and soy-based products, for example.

Stephen H. Safe, a professor of veterinary physiology and pharmacology at Texas A&M University, said that overall, despite our poor diets, "what does the data say about our health in this country? We're living longer . . . You know, where are these endocrine threats?"

Still, concerns that human health might be in danger have led to recent bans on certain phthalates in young children's toys imposed by the European Union and the City of San Francisco.

Activists in the United States have attacked the EPA for what they believe is a delayed response to the problem. The agency has defended itself by saying that it has spent millions on other research programs looking at ways to identify and limit endocrine disruptors and that it hopes to begin the long-delayed chemical testing program next year.

Some activists fear that damage is already being done. They caution avoiding plastic baby bottles, which could contain bisphenol A, and reducing consumption of animal fat, where some environmental pollutants can concentrate.

"I feel terrible because we haven't moved on this faster," said Colborn, the activist who has served as an unofficial leader among endocrine-disruptor researchers. "This is a transgenerational problem that is undermining the integrity of humans."

But Paul Foster, an official who evaluates risks to human reproduction at the National Institute of Environmental Health Sciences, said it was hard to give useful advice at this point because the chemicals being investigated are so ubiquitous.

"There's very little that they can do," said Foster, whose agency is part of the National Institutes of Health. "That's why you can't be too alarmist about it, because you can't stop people living."