Can PCBs harm boy birthrate?

Adding to a growing body of evidence that suggests environmental pollution may have an impact on the proportion of male births around the world, a new study from the US states that women exposed to polychlorinated biphenyls may be less likely to give birth to boys.

The results, published in the open access journal Environmental Health: a Global Access Science Source​ come from a study of mothers and fathers around the Great Lakes region of the United States who have eaten large quantities of contaminated fish. Contamination of the Great Lakes with polychlorinated biphenyls (PCBs) has led to the concentration of these chemicals in the fatty tissue of fish, particularly large predator species favoured by sport fishermen.​

Manufacture of PCBs, man-made chemicals used until the late 1970's as coolants and lubricants, was stopped in the US over twenty years ago because of concerns about contamination in the environment and effects on health. According to the journal article, eating fish from the Great Lakes has been associated with a reduction in the birth weight of babies, a shortened menstrual cycle, reduced fertility, and neurologic disorders.​

Although human studies have yet to show any conclusive effect of the impact of PCBs on the proportion of male offspring produced by a mother, Marc Weisskopf from the Harvard School of Public Health and Henry Anderson and Lawrence Hanrahan from the Wisconsin Department of Health and Family Services set out to investigate the PCB levels in the blood of parents from the Great Lakes region in a bid to understand the possible PCB impact on newborns.​

The researchers interviewed sport fishing charter boat captains to identify those that had eaten large quantities of potentially contaminated fish. Randomly selected members of the community who lived in a similar geographic area and were of a similar age as the charter boat captains were also contacted to identify individuals with very low consumption of fish caught in the Great Lakes by sport fisherman.​

Blood samples were taken from charter boat captains and their spouses who reported the highest levels of fish consumption and selected members of the community. Comparing the levels of PCBs found in the blood samples of their volunteers with the gender of their children allowed the research team to establish the effects of PCB consumption on the chances of conceiving a boy or a girl.​

According to the scientists, their findings suggest a clear connection between high levels of PCBs in the blood of women and a reduction in their chance of conceiving a boy.​

"Our data suggest that maternal exposure to PCBs before pregnancy, in this case primarily through consumption of contaminated fish from the Great Lakes, is associated with a decrease in the sex ratio of offspring," concluded the team. "There was some suggestion in our data that some levels of paternal exposure to PCBs may increase the sex ratio, but these results were weak and not consistent," they added.​

Despite the findings, the scientists warn that caution is needed when interpreting the results of this study as blood samples were taken some time after conception.