29 November 2012
Fetal pollutant "burden" increases with age
Most women exceed the median blood level for multiple environmental pollutants (lead, mercury, and PCBs) that could damage the brain development of fetuses and babies, say Brown University researchers. All but 17 percent of the women aged 16 - 49 were at or above the median blood level for one or more of these chemicals, which are passed to fetuses through the placenta and to babies through breast milk. The study, published in the journal Environmental Research, identified several risk factors associated with a higher likelihood of a median-or-higher "body burden" for two or more of these chemicals.
Lead, mercury, and PCBs are of greatest interest because they are pervasive and persistent in the environment and can harm fetal and infant brain development, albeit in different ways, said study author Dr. Marcella Thompson. But scientists don't yet know much about whether co-exposure to these three chemicals is more harmful than exposure to each chemical alone. Most researchers study the health effects of exposure to an individual chemical, not two or three together. "Our research documents the prevalence of women who are exposed to all three of these chemicals," said Thompson. "It points out clearly the need to look at health outcomes for multiple environmental chemical co-exposures."
Interestingly, the researchers found several statistically significant risk factors. The most prominent among them was age. As women grew older, their risk of exceeding the median blood level in two or more of these pollutants grew exponentially to the point where women aged 30 - 39 had 12 times greater risk and women aged 40 - 49 had a risk 30 times greater than those women aged 16 - 19.
Thompson said women aged 40 - 49 would be at greatest risk not only because these chemicals accumulate in the body over time, but also because these women were born in the 1950s and 1960s before most environmental protection laws were enacted.
One risk factor significantly reduced a woman's risk of having elevated blood levels of the pollutants, but it was not good news: breastfeeding. Women who had breastfed at least one child for at least a month sometime in their lives had about half the risk of exceeding the median blood level for two or more pollutants. In other words, Thompson said, women pass the pollutants that have accumulated in their bodies to their nursing infants.
Although the study did not measure whether women with higher levels of co-exposure or their children suffered ill health effects, Thompson said, the data still suggest that women should learn about their risks of co-exposure to these chemicals well before they become pregnant. A woman who plans to become pregnant in her 30s or 40s, for example, will have a high relative risk of having higher blood levels of lead, PCBs, and mercury. "We carry a history of our environmental exposures throughout our lives," Thompson concluded.
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Source: Brown University