New research published in the open access journal, Environmental Health: a Global Access Science Source suggests that women exposed to polychlorinated biphenyls are less likely to give birth to boys. The results 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. These findings add to a growing body of evidence suggesting that environmental pollution may be responsible for changes in the proportion of male births around the world. 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. PCBs are man-made chemicals, used until the late 1970's as coolants and lubricants. Manufacture of PCBs was stopped in the US over twenty years ago because of concerns about contamination in the environment and effects on health. 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.
For much of the twentieth century the global proportion of male births has been declining. Some animal studies suggest that exposure to PCBs may lower the proportion of male offspring produced by a mother. However human studies have yet to show any conclusive effect of PCBs. In an attempt to examine the effects of PCB consumption on the gender of newborns, Marc Weisskopf from the Harvard School of Public Health and Henry Anderson and Lawrence Hanrahan from the Wisconsin Department of Health and Family Services investigated the PCB levels in the blood of parents from the Great Lakes region.
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.
The results show a clear connection between high levels of PCBs in the blood of women and a reduction in their chance of conceiving a boy. The research team conclude, "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. 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."
The results of this study add to an increasing body of evidence that chemical pollutants can have effects on the chances of giving birth to a boy or a girl. However caution is needed when interpreting the results of this study as blood samples were taken some time after conception.
