"It is extremely important to conduct cumulative risk assessments to protect public health," said Dr. Sheela Sathyanarayana, acting assistant professor of pediatrics at University of Washington. "Unlike in scientific experiments, humans are exposed to multiple chemicals everyday," she said, so combining the chemicals "can help identify how these multiple exposures could be leading to health outcomes in the general population."

Swan and Sathyanarayana were not on the panel, but both have studied phthalates. Sathyanarayana's research linked babies’ phthalates to baby lotions, powders and shampoos. Swan and her colleagues reported in 2005 that the chemicals were associated with signs of feminized genitalia in newborn boys.

Tests conducted by the U.S. Centers for Disease Control and Prevention show that nearly all people, even newborns, carry traces of numerous phthalates in their bodies. Fetuses, infants and children are considered most at risk.

Europe and the United States have restricted phthalates in toys and other children's products, and the EU has banned some in cosmetics. But a variety of phthalates are still in a host of consumer products.

A child may ingest phthalates through chewing on a rubber duck, an infant may be exposed from intravenous tubes in neonatal wards, and a fetus may absorb them through his mother's use of perfumes, lotions, nail polishes and other cosmetics.     

Industry groups have argued that there is insufficient evidence to group phthalates together. But the panel of 13 scientists disagreed.

"Our committee concludes that there are common adverse effects" for many phthalates and "we believe that EPA should go ahead and conduct a cumulative risk assessment," Cory-Slechta said. She said the scientists found sufficient data, primarily from laboratory animal tests, to justify the new approach for phthalates immediately.

"There is a growing body of literature, particularly in rats, showing effects of phthalates on development of the male reproductive system," she said.

Several types of phthalates mimic or block testosterone and other androgens, which are the sex hormones that guide formation of testicles, sperm and other parts of the male reproductive system. In animal tests, exposure leads to infertility, malformed penises and abnormal testicles, which scientists call the "phthalate syndrome."

In the past, EPA has done cumulative risk assessments when substances were structurally similar in their chemical makeup or acted in the same way. But the committee says the EPA should instead group compounds according to "what they ultimately do"—the effects on human health, Cory-Slechta said.

The American Chemistry Council, representing industries that produce phthalates, said Thursday that it has "some reservations about how to conduct the cumulative risk assessment on substances" that do not act in the same way.

"This is remarkably ambitious and could be problematic for EPA considering that this essentially could result in a study without limits, financially or otherwise," said Chris Bryant, managing director of the group's Chemical Products & Technology Division.

"Congress has asked the Consumer Product Safety Commission to conduct a cumulative risk assessment on phthalates and there is a question as to whether a simultaneous EPA study would be redundant," he assed.

The chemical industry also wonders how this would be reconciled with another National Academy report earlier this month that advised EPA to more strongly focus its risk assessments for chemicals.

Cory-Slechta agreed that a cumulative assessment would mean a "real paradigm change for EPA" and "might prove somewhat challenging for them." One obstacle for EPA scientists is that not all phthalates have the exact same effects or the same potency.