PCB levels were taken from men who fished in Lake Michigan
Scientists in the US looked at data from three studies in which levels of polychlorinated biphenyls (PCBs) were measured in the bodies of men who ate fish taken from Lake Michigan.
More than 57% of 208 children born to the men, were boys, a paper in the Journal of Occupational and Environmental Medicine reveals.
PCBs are among a number of environmental contaminants that have plagued the Great Lakes for years.
Professor Wilfried Karmaus, who led the study, said: "We do not wish to say that having a baby boy is bad. It's just that there were more of them.
"A change in the proportion of boys to girls, however, indicates that environmental contaminants may play a role in human reproduction."
PCBs have been linked to liver and kidney cancer, birth defects and more recently to hindering babies' brain development in the womb and after birth.
Although they are now banned, these chemicals, which disrupt the human hormone system, were once widely used in industry as coolants and lubricants.
Long-term threat
They are still being leaked into the environment from old electrical equipment. Once there, they do not readily break down, and pose a long-term threat.
They are usually found in our food, and naturally accumulate in fat, with high concentrations in meat and oily fish.
Friends of the Earth (FoE), which is spearheading a Safer Chemicals campaign, said the US study reinforced the dangers of PCB exposure.
FoE biochemist Dr Michael Warhurst said: "This is another piece of research raising concerns about PCBs.
"In our view, we should not be contaminating our bodies with any long-lived chemicals.
"The lesson of PCBs is that even if you think a chemical is safe now, you may change your mind in 20 years' time."
The US team restricted its research to children born after 1963 and to families where PCB levels were detectable in both fathers and mothers.
This amounted to a total of 208 children from 101 families. They found men with PCB concentrations of at least 8.1 micrograms per litre of blood were more likely to father boys.
Professor Karmaus said: "We did not detect that the PCB levels of mothers affected the number of boys or girls."