However, the researchers also found evidence of increased exposure to other phthalates that could pose similar health risks.
Phthalates are used to make plastic more flexible, and are found in items such as nail polish, fragrances, plastic products and building materials. In 2009, the U.S. Congress voted to ban some of the chemicals from children's products because of their disruptive effects on human hormones.
"Exposure to three of the phthalates that have been banned in children's toys has decreased over 10 years," said lead researcher Ami Zota, an assistant professor of environmental and occupational health at George Washington University's School of Public Health and Health Services.
For other phthalates, however, exposure has increased, Zota said. "[The increase is] probably because these new phthalates are replacing the phthalates that have been phased out," she said.
Some of these newer phthalates have been studied in animals and found to be just as harmful as the banned phthalates, Zota added. "We are uncertain about their potential human health effects," she said.
Zota said she thinks companies are replacing the banned chemicals with phthalates that haven't been banned.
Although she could not say whether all phthalates should be banned, Zota said the lesson of the continuing phthalate story is a simple one: "We need to do a better job of understanding the health and safety ramifications of chemicals before they're used in a widespread manner," she said.
The report was published online Jan. 15 in the journal Environmental Health Perspectives.
Some studies have linked phthalates to DNA damage in sperm and lower sperm quality in men. Other research has found that exposure among pregnant women might alter genital development in their male children. Exposure to phthalates also has been linked to thinking and behavioral problems in boys and girls, the researchers said.
In a statement, the American Chemistry Council, a trade association for U.S. chemical companies, said there is scant evidence that phthalates are harmful.
"Information collected by the U.S. Centers for Disease Control and Prevention over the last 10 years indicates that, despite the fact that phthalates are used in many products, exposure is extremely low -- much lower than the levels considered safe by regulatory agencies," the statement said.
"It is worth noting, however, that the [new study] tells us nothing about the migration rate of any particular [phthalate] from flexible vinyl; nothing about how the [phthalate] might break down in the environment; and nothing about whether minute amounts of the [phthalate] might present any sort of environmental or health issue," the statement added.
On the other side of the issue, Johanna Congleton, a senior scientist at the environmental-advocacy organization Environmental Working Group, said, "While we are pleased that the levels of certain bad actor phthalates have declined in the U.S. population, it is worrisome that the body burdens of other types of phthalates have increased."
"Research tells us that replacement phthalates may have similar health impacts, such as adverse effects on hormone signaling and male reproductive development," Congleton said." Swapping out one problematic chemical for another that may be just as bad is not the answer. Clearly we need better safety testing for chemicals before they come to market, so we can be sure that replacement chemicals are truly greener."
For the study, Zota and her colleagues looked at exposure to phthalates from 2001 to 2010 among 11,000 people who took part in the U.S. National Health and Nutrition Examination Survey.
The researchers found that almost everyone had been exposed to some phthalates, including those that had been partially banned.
Among all phthalates, three have been permanently banned in all children's products. Another three were temporarily banned, pending further study, from use in children's toys that might be placed in the mouth.
Zota's team found that exposure to permanently banned phthalates decreased.
However, exposure to the phthalates that were banned until further study is conducted (DnOP, DiDP and DiNP) actually increased. DnOP and DiDP exposure increased 15 percent and 25 percent, respectively, and exposure to DiNP increased nearly 150 percent. DiNP is being used to replace other phthalates, the researchers said.
In addition, the researchers found changes in exposures to the other two phthalates (DEP and DiBP), neither of which has been subject to federal restrictions. Exposure to DEP decreased by 42 percent since 2001, but tripled for DiBP.
Zota said consumers who are worried about exposure to phthalates should look for phthalate-free products, which are becoming more widely available.
Visit the U.S. Centers for Disease Control and Prevention for more on phthalates.
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