Some plastics contain additives like bisphenol A (BPA) and phthalates. These have been found to be harmful in animal studies, said Dr. Wade V. Welshons of the University of Missouri in Columbia. And the Centers for Disease Control has detected them in the urine of a majority of the thousands of people it has tested in the United States.

BPA is approved by the Food and Drug Administration for use in polycarbonate packaging for all types of food "based on numerous safety tests," according to the Society of the Plastics Industry, a trade group. But Dr. Welshons said a re-evaluation is needed, focused on the last five years of research. Many plastic bags and wraps are made with 100 percent polyethylene, so Dr. Trasande and others call them safer.

Ms. Lilley began buying organic foods nine years ago, when she became pregnant with her first child. Since then, the newsletter from the Puget Sound Community Co-op, where she shops, combined with Web research, has persuaded her to buy wax paper bags, dye-free detergent and other cleaners that emphasize natural ingredients. "There's so much out there that I can't protect them from," she said of her children. "At least their home and the food they eat should be as safe as I can make it."

Scientists can detect toxic chemicals in remarkably small concentrations in the environment and in foods, and even in umbilical cord blood. But studies showing that certain chemicals in high concentrations are damaging to lab animals may not indicate similar health effects from the much smaller doses to which humans are exposed, said Dr. David Eaton, director of the University of Washington's Center for Ecogenetics and Environmental Health. "Of course we should try to keep toxins out of our air, food and water," he said, "but my motto is 'prudence without paranoia.' "

The difficulty for consumers is knowing which, if any, changes to make in what they buy. And the decisions don't stop at organic foods.

Expert opinions vary widely, and the gray area is vast. Dr. Charles M. Yarborough, a member of the Children's Health Protection Advisory Committee of the E.P.A., said there were almost no easy answers for parents. "It's hard to say something is dangerous or not dangerous," he said. "There are questions of exposure levels, the age of the child, the toxicity of the chemical and other factors." He added, "After all, water is toxic if you drink too much too fast."

Dr. Trasande says children are especially vulnerable to toxins because their body systems are developing. "Once they go off track, you can't hit the rewind button," he said. Because of their lower body weight and proximity to the ground, where residue may linger, children feel the effects of household chemicals more than adults, he said.

Jeffrey Hollander, president of Seventh Generation in Burlington, Vt., says he has witnessed a growing interest in his company's nontoxic, biodegradable household products, like laundry detergent. He attributes this in part to new parents who suddenly find familiar cleaners less attractive.