Maternal Smoking and Exposure to PCB Chemical Linked to Low Birth Weight
March 24, 2017
Prenatal exposure to both cigarette smoke and environmental chemicals causes greater harm than exposure to each individually
Oakland, CA—Women who were exposed to higher levels of a toxic byproduct of a common PCB chemical and who also smoked during pregnancy had babies with significantly lower birth weight, according to a new study from the Public Health Institute published in the journal Reproductive Toxicology. This is the first-ever human study on the impacts of exposure to PCB byproducts—known as hydroxylated polychlorinated biphenyls (OH-PCBs)—during pregnancy.
“This study provides direct evidence that some of the impact of smoking is enhanced by co-exposure to this industrial chemical,” said one of the study’s authors, Barbara A. Cohn, PhD, of the Public Health Institute’s Child Health and Development Studies in Oakland, CA. “It is proof of the concept that something like smoke exposure and environmental chemicals can work together to create more damage than each could alone.”
OH-PCBs are secondary contaminants that are produced when the body breaks down PCBs. Although PCB production was banned in the U.S. in the 1970s, the chemicals do not readily break down once in the environment, so they remain widespread in air, water and soil, and in the bodies of wildlife and humans. Many women were exposed to high concentrations of PCBs in the 1960s, at a time when rates of cigarette smoking were also high.
The researchers found that:
- Independent of the mother’s maternal thyroid hormone levels and BMI, compared to nonsmokers, smokers had twice the mean concentration of the toxic byproduct 4-OH-CB107 and lower levels of its parent compound, PCB118.
- Among mothers who smoked, the birth weight of newborns with maternal concentrations of 4-OH-CB107 in the upper quartile was 316 grams (about 11 ounces) lighter than those with maternal concentrations in the lowest quartile.
- Maternal prenatal 4-OH-CB107 levels appeared to be influenced by maternal smoking and to contribute to lower birth weight among the babies of smokers.
Low birth weight is strongly linked to health problems later in life, including obesity, diabetes and cardiovascular disease.
"This paper shows that mixtures matter,” Cohn said. “It may also explain why some studies show stronger effects of chemical exposures than others. Our bodies are not exposed to chemicals and other environmental hazards in isolation, so the way we design studies should also look at combinations of exposures.”
PHI’s Child Health and Development Studies studied 20,754 pregnancies among women who were members of the Kaiser Foundation Health Plan in the Oakland, CA, metropolitan area from 1959 to 1967. Researchers analyzed stored blood samples taken from the mothers during pregnancy to measure levels of PCB and OH-PCB exposure in the womb, and examined medical records for data on four pregnancy outcomes: birth weight, gestational length, birth length and head circumference.
The researchers randomly selected 600 participants to be included in the study, and among these, 442 had OH-PCB measurements. Of this number, 76 smoked during pregnancy. There were no large or significant differences in infant birth weights, maternal smoking rates, occupation, race, body mass, or parity between those where OH-PCB measurements were available and those where measurements were not available because their serum had been assessed previously.
“Our findings should encourage new work on whether common exposures similar to cigarette smoke, such as air pollution, also collaborate with environmental chemicals to magnify potential harm,” Cohn said. “The answer to this question might help us target people or places where both types of exposures are highest in order to prevent harm.”
Other authors of the study include: Katrina Kezios, Yiwei Gu and Pam Factor-Litvak of the Mailman School of Public Health at Columbia University; Piera Cirillo of the Public Health Institute’s Child Health and Development Studies; and Darcy Tarrant, Myrto Petreas and Jun-Soo Park of the California Department of Toxic Substances Control.
The research was supported with funding from the National Institute of Environmental Health Sciences.
The study, “Hydroxylated Polychlorinated Biphenyl Metabolites (OH-PCBs), Maternal Smoking and Size at Birth,” is published online at http://www.sciencedirect.com/science/article/pii/S089062381630377X.
About the Child Health and Development Studies
The Child Health and Development Studies (CHDS) is a project of the Public Health Institute. CHDS is committed to investigating how health and disease are passed on between generations—not just by genes, but also through social, personal, and environmental surroundings.
About the Public Health Institute
The Public Health Institute, an independent nonprofit organization, is dedicated to promoting health, well-being and quality of life for people throughout California, across the nation and around the world.