By Raloff, Janet
Science News , Vol. 158, No. 10
Ingredients of common plastics, may harm boys as they develop
Phthalates. Difficult to spell and harder to sound out, this class of compounds would be forgettable if the name didn't keep popping up in debates over the safety of intravenous-blood bags, food packaging, and children's toys.
Phthalates have become ubiquitous in modern society. Some of these oily substances find use as solvents, but most serve as softeners that make rigid materials turn flexible. Worldwide, manufacturers produce an estimated billion pounds of phthalates annually.
Despite a half century of apparently safe use, several environmental and health groups and the U.S. Consumer Product Safety Commission in late 1998 called for the manufacturers of toys, baby pacifiers, and medical supplies to remove the most toxic of these chemicals from their products. At that time, scientists had linked cancer in adults to heavy exposure to some phthalates, animal studies had indicated that phthalates never cause organ damage, and chemists had demonstrated that phthalates could leak from plastics during use.
At least a few phthalates also have the potential to disrupt boys' reproductive development. Or so a federally appointed "panel of experts" has just concluded after 15 months of deliberation and a review of some 1,000 studies.
The new phthalate review was commissioned by the National Toxicology Program's Center for the Evaluation of Risks to Human Reproduction (CERHR). It was the first project of this 2-year-old center, which is part of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C.
The review focused exclusively on the compounds' potential for causing birth defects or reproductive abnormalities. Over the past 3 years, animal experiments have indicated that low exposures can grossly alter the organs that in adults produce and deliver sperm.
The evaluators noted, however, that low phthalate concentrations show damage to animals only when the exposure takes place during some precise window of vulnerability. This period in test animals approximately corresponds to the end of a woman's first trimester of pregnancy, a time when many women don't yet realize they're carrying a child.
Several health and environmental advocacy groups have trumpeted the panel's assessments, renewing their call for a phaseout of targeted products containing certain phthalates. The CERHR panel itself didn't go that far. In fact, the group argued that panic is unwarranted.
Except for data on the most widely used phthalate, di-2-ethylhexyl phthalate (DEHP), much of the human-exposure and reproductive-toxicity data now available are rather preliminary or sketchy, the panel observed. Moreover, could identify only a few, relatively small populations that might encounter significant exposures during periods when vulnerable tissues are developing. And, in at least some cases, it concluded, any risks from phthalate exposure might be outweighed by the benefits such products offer.
Still, notes panel chairman Robert J. Kavlock, who directs reproductive toxicology at the Environmental Protection Agency in Research Triangle Park, "I don't think we gave a clean bill of health to any [phthalates]. We didn't say there was no risk."
Though his panel slogged through nearly 600 studies on DEHP and almost as many for another six phthalates, it didn't find answers to many pressing questions about developmental toxicity. Lingering doubts about the phthalate's toxicity, after so many studies, "seems to speak to the fact that somehow the right studies weren't being conducted," observes CERHR director Michael D. Shelby.
One reason, Kavlock notes, is that researchers had designed most phthalate studies to evaluate risk of cancer or infertility in adults exposed to the chemicals in the workplace.
"Most of those data were also 20 years old or more," adds panelist Paul M. …