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While the consensus favors a fat connection, other explanations haven't been ruled out. One is chemical pollution in the food chain--specifically, DDE, a breakdown product of the pesticide DDT, and PCBs, once used as flame retardants in electrical equipment. Both chemicals are plausible suspects because they mimic hormones that play a key role in the development of the reproductive system. Beyond that, says Dr. Walter Rogan, an epidemiologist at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., both chemicals are ubiquitous in the environment, and they persist in the body for years after exposure.
For that reason, he chose PCBs and DDE for one of the very few large, long-term studies of chemical exposure and puberty in humans. Rogan and his colleagues began with some 600 pregnant women, measuring concentrations of the chemicals in their bodies. When their babies were born, the researchers then measured levels in the mothers' breast milk. Finally, the team monitored the children as they grew and entered puberty.
The most prominent effect, reported last spring in the Journal of Pediatrics, was that boys exposed to DDE and girls exposed to PCBs were heavier than their unexposed peers at age 14. The study also noted an intriguing fact: girls with high prenatal PCB exposure tended to hit the first stages of puberty a bit earlier than others. Rogan stresses that the numbers were too low to be statistically significant. "If there is an effect of environmental chemicals on puberty," he says, "it's pretty small, because we studied these kids in detail over a long period of time, and we didn't see it." But, Rogan adds, "I can't rule it out."
Could other substances besides PCBs and DDE influence sexual development? Perhaps, Rogan says. But few compounds are as persistent and pervasive. Hormones given to livestock, for instance--another frequently invoked possibility--break down very quickly in the body. "I have not studied the effects of hormones in beef or dairy cattle," Rogan says. "It's not something I'm running out to study either."
What merits another look, some researchers believe, is a suite of chemicals used to make plastics. One is Bisphenol A, or BPA. Like DDE and PCBs, it is a chemical cousin of estrogen's, and it has been shown to affect the reproductive systems of lab mice. Another category of plastics ingredients, phthalates, may have played a role in a rash of cases of very early puberty in Puerto Rico back in the 1980s, with girls as young as 2 growing breasts and pubic hair. And while no cause has yet been determined, a study published last month suggests that a possible culprit could be phthalates, which are used, among other things, to make plastics flexible. It's by no means an ironclad case, however, and the plastics industry doubts that there's any link. But, says Rogan, "what went on in Puerto Rico is a good question and one that needs more study."