By Rachel Ehrenberg, Science News
Keeping plasticizers in their place has always been a slippery task. The compounds that add flexibility to harder plastics may also migrate from these materials, raising health concerns about human exposure via medical devices or children's toys.
Now, scientists working with the widely used plasticizers known as phthalates have locked down these compounds, preventing them from migrating. The research, published in the March 9 Macromolecules, may lead to improved versions of hard plastics that don't leach their ingredients.
The research team, led by Helmut Reinecke of the Institute of Polymer Science and Technology in Madrid, Spain, worked with the phthalate known as DEHP (Di(2-ethylhexyl) phthalate). They first added a compound incorporating a sulfur group to DEHP and then mixed this decorated phthalate with polyvinyl chloride (PVC). The sulfur bumped a chlorine atom aside, double-bonding the phthalate to the PVC backbone.
The scientists then tested the material by putting it in a solvent that typically prompts migration of phthalates. "In our case it is impossible to get it out," says Reinecke. They detected no trace of free phthalates even after five hours of soaking; usually after three hours, he says, all of the phthalate would be released.
Tying down the phthalate does change the properties of the PVC, comments polymer scientist James Summers, a consultant in Bay Village, Ohio. Such additives can make materials leathery, where rubbery is preferred.
The 1999-2000 National Health and Nutrition Survey, which takes a periodic snapshot of the health and nutritional status of people living in the United States, detected phthalate metabolites in more than 75 percent of the population. Several studies have suggested that phthalates meddle with hormonal pathways and disrupt boys' reproductive development.
In 2009 the Environmental Protection Agency added phthalates to a list of "chemicals of concern." The Consumer Product Safety Improvement Act of 2008 also banned some phthalates from children's toys.
New work adds to the list of concerns: Jennifer Weuve of the Rush University Medical Center in Chicago and colleagues report finding a weak link connecting phthalate exposure and endometriosis, a condition where uterine tissue grows outside the uterus and can cause infertility and other problems. The link, reported in an upcoming issue of Environmental Health Perspectives, is not strong, but intriguing, says Weuve.
Preventing phthalate migration is important, she notes. "It at least addresses the mechanism by which we think people are being exposed."