The study was carried out by Michigan State University using data from three separate studies in which PCB levels were measured in the bodies of men who ate fish taken from Lake Michigan. PCB pollution has plagued the Great Lakes for years.

The research revealed that – as well as the more well-known dangers of PCBs, such as being possible carcinogens – of the 208 children born to the men in the study after 1963, more than 57% were boys.

“We do not wish to say that having a baby boy is bad, it’s just that there were more of them,” said MSU Associate Professor of Epidemiology Wilfried Karmaus, who directed the study. “A change in the proportion of boys to girls, however, indicates that environmental contaminants may play a role in human reproduction.”

“However, we did not detect that the PCB levels of mothers affected the number of boys or girls,” said Karmaus.

The research is published in the Journal of Occupational and Environmental Medicine.

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