FRIDAY, Feb. 15, 2002 (HealthDayNews) -- By most accounts, the toxic chemicals known as PCBs are bad news. They're suspected of causing memory loss, stunted growth and cancer.
However, scientists now think they may cause something else -- a bumper crop of baby boys.
A study of Great Lakes fishermen found that fathers exposed to high levels of PCBs are significantly more likely to have male children than other fishermen. However, the chemicals seem to have no effect when only mothers are exposed.
The meaning of the findings isn't clear, but the toxins may have more biological effects than people realize, says lead author Wilfried Karmaus, a professor of epidemiology at Michigan State University.
"Having boys is not a disease, and being a boy is not a disease," Karmaus says. "But this shows that PCBs may interfere with human reproduction."
Polychlorinated biphenyls (PCBs) were widely used in electrical equipment and hydraulic fluids until the federal government banned them in the late 1970s because of suspicions they may cause cancer. Due to toxic waste dumping, PCBs were prevalent in the Great Lakes, and they contaminated fish that were eaten by people.
PCBs remain in the Great Lakes, at levels far beyond those considered safe. However, experts say the levels are much lower than they were in the 1970s because of clean-up efforts.
Researchers examined three studies that looked at PCB levels in people who ate fish taken from Lake Michigan. The subjects were initially studied from 1973-1974, 1979-1982 and 1989-1991.
In the new study, researchers tried to find people who had high levels of PCBs. By the summer of 2000, Karmaus and his colleagues had found 101 of the original families studied.
They then asked the family members about the genders of children they had as far back as 1963. "We were interested in the health risks for the second generation," Karmaus says.
The 101 families had 208 children, and 57 percent were male. Men with high levels of PCB concentrations -- at least 8.1 micrograms per liter of blood -- were more likely to father boys.
The Michigan State researchers also looked at a comparison group of fishermen who did not have high PCB levels; 45 percent of their kids were boys.
Normally, 52.5 percent of babies are male. But infant males are weaker than females, and have a higher infant mortality rate. As the babies grow, the ratio of males-to-females eventually becomes near one-to-one as some of the males die.
Previous studies gave conflicting results about whether PCBs affect the gender of babies, Karmaus says.
The new findings appear in the February issue of the Journal of Occupational and Environmental Medicine.
The researchers found no links between mothers with high PCB levels and higher numbers of baby boys or girls, Karmaus says.
"There must be some kind of influence that's carried with the sperm [from fathers]," he says.
It's not clear when the PCBs change the gender ratio, Karmaus says. "It may be that the loss of girls during pregnancy from conception to birth is higher," he says.
"During pregnancy, about 60 to 70 percent of all conceptions are lost, most very early," Karmaus explains. "They cannot survive. It's a normal selection process."
Dr. Walter J. Rogan, an epidemiologist who studies PCBs for the National Institute of Environmental Health Sciences, urges caution in interpreting the Michigan State research. Scientists next need to turn to animal studies to figure out whether PCBs actually do affect reproduction, he says. In the studies, PCBs would be fed to animals to see if they give birth to higher numbers of males or females.
Scientists have historically "tried to observe things in people, and then try to figure out why those things happen [back] in the lab," Rogan says.
What To Do: For more on the dangers of PCBs, visit Health Canada or the U.S. Environmental Protection Agency.
