Men who eat fish with pcbs likely to father boys
Men who eat fish from the Great Lakes, which are laced
with such toxic industrial chemicals as PCBs, conceive
a disproportionately high number of sons, according to
The strange effect that PCBs seem to have on sex ratios
is poorly understood, but is too significant to pass off
as mere coincidence, said Wilfried Karmaus, a professor
of epidemiology at the University of Michigan.
He suggested the effect might be due to a disruption
of hormone levels in the male reproductive system, which
has been documented in other, more severe cases of PCB
Dr. Karmaus followed nearly 400 families who regularly
ate various fish -- walleye, carp, salmon, trout, among
others -- they caught in Lake Michigan. Of the 208 children
born to the men with the highest PCB content in their
blood, 57% of them were boys.
This figure is statistically far higher than the worldwide
average sex ratio in which about 52% of newborns are male.
Females outnumber males in most populations, though, due
to their longer average lifespan and lower mortality rates.
Strangely, the mother's exposure to PCBs had no significant
effect on sex ratios, despite the close physiological
contact between mother and fetus.
"Being a boy is not a disease," said Dr. Karmaus, the
lead researcher on the report in the current Journal of
Occupational and Environmental Medicine, "but we can show
that there are some health effects on human reproduction
Dr. Karmaus said the phenomenon of skewed birth rates
is likely mirrored in fishermen on each of the Great Lakes.
PCBs, or polychlorinated biphenyls, were in wide industrial
use from the 1930s to the 1970s, figuring as ingredients
in paints, caulking and electrical coolants and insulators.
Concern about their toxic effects led to a continent-wide
ban on importing and producing PCBs in 1977, but the persistent
chemicals decompose at such a slow rate that they are
still found at dangerous levels in Great Lakes fish.
The Ontario Ministry of the Environment has issued specific
warnings about PCBs in fish and their harmful effects
on expectant mothers, but their guide to edible sport
fish does not mention effects on male reproductive health.
Mike Wade, a toxicology researcher at Health Canada,
said Dr. Karmaus' findings are the latest in the controversial
field of sex ratio studies, and they fly in the face of
"The more boys per girls, in my experience, is kind of
novel," Dr. Wade said. "Usually it's the other way around
with occupational or drug related factors. For example,
guys who are taking chemotherapy tend to have fewer boys
The explanation for the skewed birth rate around Lake
Michigan is probably hormonal, Dr. Karmaus said, but PCBs
may also have some as-yet-unknown toxicological effect
on the male fetus, which is known to be more fragile than