It’s also well established that Western women are beginning puberty earlier, and going through menopause later. Dr. Maida Galvez, a pediatrician who runs Mount Sinai’s pediatric environmental health specialty unit, told the symposium that American girls in the year 1800 had their first period, on average, at about age 17. By 1900 that had dropped to 14. Now it is 12.

A number of studies, mostly in animals, have linked early puberty to exposure to pesticides, P.C.B.’s and other chemicals. One class of chemicals that creates concern — although the evidence is not definitive — is endocrine disruptors, which are often similar to estrogen and may fool the body into setting off hormonal changes. This used to be a fringe theory, but it is now being treated with great seriousness by the Endocrine Society, the professional association of hormone specialists in the United States.

These endocrine disruptors are found in everything from certain plastics to various cosmetics. “There’s a ton of stuff around that has estrogenic material in it,” Dr. Goldfarb said. “There’s makeup that you rub into your skin for a youthful appearance that is really estrogen.”

More than 80,000 new chemicals have been developed since World War II, according to the Children’s Environmental Health Center at Mount Sinai. Even of the major chemicals, fewer than 20 percent have been tested for toxicity to children, the center says.

Representative Louise Slaughter, the only microbiologist in the House of Representatives, introduced legislation this month that would establish a comprehensive program to monitor endocrine disruptors. That’s an excellent idea, because as long as we’re examining our medical system, there’s a remarkable precedent for a public health effort against a toxic substance. The removal of lead from gasoline resulted in an 80 percent decline in lead levels in our blood since 1976 — along with a six-point gain in children’s I.Q.’s, Dr. Landrigan said.

I asked these doctors what they do in their own homes to reduce risks. They said that they avoid microwaving food in plastic or putting plastics in the dishwasher, because heat may cause chemicals to leach out. And the symposium handed out a reminder card listing “safer plastics” as those marked (usually at the bottom of a container) 1, 2, 4 or 5.

It suggests that the “plastics to avoid” are those numbered 3, 6 and 7 (unless they are also marked “BPA-free”). Yes, the evidence is uncertain, but my weekend project is to go through containers in our house and toss out 3’s, 6’s and 7’s.