Americans are exposed to phthalates and other potential endocrine disrupting chemicals, and the Environmental Protection Agency needs to study the cumulative effect of this exposure in determining the health risk, according to a report by the National Research Council, the premier U.S. scientific organization.
Because many chemicals share the ability to mimic hormones at low levels, the EPA needs to consider how various chemicals interact and affect the body. Now, the EPA typically reviews the health risk of chemicals based on the chemical structure of each compound, rather than common health impacts of multiple chemicals.
Several phthalates are to be banned in U.S. children's products in 2009 (though products for sale this Christmas are not subject to the ban), and Europe has gone farther by banning several phthalates used in cosmetics. For the first time, cosmetics makers will report their use of phthalates to the EPA, but it's still virtually impossible for consumers to determine which products contain phthalates from reading ingredient labels.
Here's how the NRC framed the need for a cumulative health assessment:
Recent animal studies have increased understanding of the potential risks from phthalates, although few human studies on the health effects of phthalates are available ... To decide whether a cumulative risk assessment is warranted, two factors needed to be determined: whether humans are exposed to multiple phthalates at any given time, and whether sufficient evidence exists linking exposures to similar adverse health effects. The committee established that recent studies have shown widespread human exposure to multiple phthalates, including in utero exposure.
Then, the committee reviewed animal research and found that exposure to various phthalates in lab animals produced similar health outcomes, including a range of effects on the development of the male reproductive system. The most notable effects in male rats are infertility, undescended testes, malformation of the penis, and other reproductive tract malformations. However, the severity of effects differs among phthalates; some exhibit less severe or no effects. Furthermore, the age of the animals at the time of exposure is critical to the severity of the effects. For example, the fetus is most sensitive. Given that multiple human exposures to phthalates occur and that research shows exposure to different phthalates leads to similar outcomes in lab animals, a cumulative risk assessment is called for, the committee said.
The animal studies reviewed by the committee also indicated that some phthalates reduce testosterone concentrations. Depending on when this drop occurs, it can cause a variety of effects in animals that are critical for male reproductive development. Other chemicals known as antiandrogens, which prevent or inhibit male hormones from working, can produce similar effects in lab animals. The committee recommended that phthalates and other chemicals that affect male reproductive development in animals, including antiandrogens, be considered in the cumulative risk assessment. A focus solely on phthalates to the exclusion of other chemicals would be artificial and could seriously underestimate risk, the committee emphasized.
Currently when conducting cumulative risk assessments, EPA often considers only chemicals that are structurally related, on the assumption that they have the same chain of reactions that lead to a final health outcome. That practice ignores how exposures to different chemicals may result in the same health effects. The conceptual approach taken for phthalates -- to consider chemicals that cause similar health effects -- should also be applied when completing any cumulative risk assessment, the committee said. For instance, EPA could evaluate the risk of combined exposures to lead, methylmercury, and polychlorinated biphenyls because all contribute to cognitive deficits consistent with IQ reduction in children.
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