Nearly 23 percent of American women of childbearing age met or exceeded the median blood levels for all three environmental chemical pollutants - lead, mercury, and PCBs - tracked in an analysis of data on thousands of women by Brown University researchers. All but 17.3 percent of the women aged 16 to 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 advance online Nov. 15 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.
The three pollutants 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 lead 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, who began the analysis as a doctoral student at the University of Rhode Island College of Nursing and has continued the research as a postdoctoral research associate for Brown University's Superfund Research Program with co-author Kim Boekelheide, professor of pathology and laboratory medicine. "It points out clearly the need to look at health outcomes for multiple environmental chemical co-exposures."
Most of the childbearing-age women - 55.8 percent - exceeded the median for two or more of the three pollutants.
Risks of exposure
Data were collected between 1999 and 2004 from 3,173 women aged 16 to 49 who participated in the Centers for Disease Control and Prevention National Health and Nutrition Examination Survey (NHANES). The survey was designed to represent the national population of 134.5 million women of childbearing age. Because the original study also elicited a wide variety of information on health behaviors, socioeconomic and demographic characteristics, Thompson and Boekelheide were able to identify specific risk factors associated with increased odds of having higher blood levels of lead, mercury, and PCBs.
They 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 to 39 had 12 times greater risk and women aged 40 to 49 had a risk 30 times greater than those women aged 16 to 19.
Thompson said women aged 40 to 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.