RISING WILDLIFE STERILITY: NOT ALL IT SEEMS

Edited by Douglas Harbrecht

Remember reports a few years ago of shrunken alligator penises and sterile panthers in Florida wetlands? They seemed to portend some mysterious new environmental danger. But follow-up studies suggest that evidence of a link between chemicals introduced by man into the environment and animal deformities may not be nearly as strong as once feared.

In a 1996 book hyped as a latter-day Silent Spring, scientists Theo Colborn and John Peterson Myers connected these problems and others to man-made chemicals in the environment. In their book, Our Stolen Future (written with journalist Dianne Dumanoski), they argued that pesticides, plastics, and other substances are capable of mimicking estrogen and other natural hormones. This witch's brew of chemicals was wreaking havoc on the biological world, causing everything from disappearing panthers to lower sperm counts and higher breast cancer rates in people, the book warned.

The idea that these chemicals are affecting people was controversial from the start. Some studies showed, for instance, that sperm counts aren't declining at all. But the animal data seemed on solid ground. In the years following a 1980 pesticide spill in Florida's Lake Apopka, most alligator eggs failed to hatch -- and males that did survive had abnormally small penises. Similarly, analysis of Florida panthers showed that males and females alike had alarmingly similar amounts of hormone levels. Scientists speculated that the males were being "feminized" by the chemicals in the environment, explaining why the big cats' testicles failed to descend normally -- and why they failed to produce enough new cubs to keep the species viable.

Now, however, some of the same scientists who raised the initial alarm have had a chance to do additional studies. And the link between estrogen-mimicking chemicals in the environment and problems with wildlife has suddenly become much more tenuous.

Timothy S. Gross, an animal physiologist with the U.S. Geological Survey's Biological Resources Div., did some of the original work on panthers and alligators. Since then, he has been able to collect about 10 times more data. His results, still unpublished, show that the warnings may have been misdirected.

In the case of the Florida panthers, Gross and colleagues were able to sample hormone levels from the big cats in Texas, South America, and zoos, where the animals have no reproductive problems. "Our hypothesis is that we'd find different hormone levels in these animals than in the Florida panthers," he explains. Not so. "We found no difference."

So there is nothing abnormal about the hormone levels in the Florida males. Then what is causing the Florida cats' problems? The leading hypothesis now is inbreeding.

For the Lake Apopka alligators, Gross and his co-workers tested the creatures for DDT, the most common pesticide in the lake. If the estrogen-mimicking idea was right, the female alligators with the highest levels of the pesticide and its by-products would have the most reproductive problems -- eggs that failed to hatch and offspring with deformed gonads.

The results: The alligators continued to have reproductive problems, but "we found no correlations with levels of DDT," Gross reports. The problems could still be caused by other chemicals, he says. But another idea being explored now is whether massive algae blooms, which also struck the lake at about the same time as the pesticide spill, could have played a role. The algae blooms produce toxins that can affect animal reproduction.

The lesson? "I believe endocrine disruption is still a potential problem in wildlife," says Gross. "But it's much more complicated than I originally thought."

By John Carey in Washington