Herman-Giddens, however, believes that these arguments do not invalidate her finding that girls are entering physical puberty much earlier, regardless of when they start their periods.

"It's sad," says Herman-Giddens now. "I think children ought to be children a little longer than the third grade. And if it keeps getting younger and younger, it will make the whole public health issue even more of a crisis than it already is. We don't know the long-term health effects that could occur."

Since the first reports about Herman-Giddens' findings, the idea of little girls becoming little women at a disturbing pace has become something of an obsession for researchers, the media and environmentalists, who have been frantically theorizing about what may be the cause. Herman-Giddens believes it's possible that even crude sexual imagery in magazines, on TV and in film could be provoking early puberty. Blame also has been assigned to the weight increase in American children and, perhaps most bizarrely, to little girls picking up stepfathers' pheromones in the absence of their biological fathers.

The impact of environmental estrogens has been something of a dark-horse theory -- until now. The Emory University study gives new force to the idea that these chemicals are the chief culprits in the controversial early puberty trend.

While Marcus stresses that we cannot be sure that other endocrine disruptors will affect girls in the same way as PBBs, she believes that we shouldn't wait until the link is well established before taking precautions. "It would be prudent to reduce our exposures now [to endocrine disruptors] rather than wait until we're sure of the damage," says Marcus, "because the only way to be sure of the damage is when the damage is already done."

PBB is one of many chemicals known as environmental estrogens -- a class so prevalent in the environment that even though some (like DDT) are banned, they still show up in our water and in the fish that we eat. There are thousands of chemicals in use today and many of those haven't been tested for estrogenic properties, but we know that environmental estrogens can be found in sunscreen lotions, plastic baby bottles, hair straighteners and nail polish. They are in the lining of food cans and in the fillings of our teeth. They have even been found in drinking water in Britain -- traceable to the hormones in birth control pills transmitted through urine into the water table and to fish. At this point, all of us have low levels of them coursing through our blood.

Artificial estrogens and estrogenic pesticides are important because they can mimic the effects of the actual estrogen in the body. Puberty begins when estrogen levels are at a peak; the way to stop a girl from reaching puberty is to give her drugs that block estrogen. Theoretically, the way to speed up puberty is to introduce more estrogen.

"I'm afraid for the next generation," says Dr. Gina Solomon, assistant clinical professor of medicine at the University of California at San Francisco and senior scientist at the Natural Resources Defense Council. "Adults are in some way resilient; we can be exposed to fairly high levels of pollutants without as much of a health effect as a fetus would get. What I'm concerned about is the mothers who are being exposed today without knowing it, exposing their fetuses and infants."

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