A study released in mid July, 2008 by
researchers at the University of California, Davis found that women exposed to high levels of polychlorinated biphenyls
(PCBs) are significantly less likely to give birth to male children than
women exposed to lower levels of the banned environmental pollutants.
The study, which appears in the open-access journal
Environmental Health, provides the strongest evidence to date that maternal
exposure to PCBs skews the ratio of male-to-female offspring in humans.
"These findings suggest that high maternal PCB
concentrations may either favor fertilization by female sperm or result in
greater male embryonic or fetal losses," says lead study author Irva
Hertz-Picciotto, an epidemiologist and professor of public health at UC
Davis. "The association could be due to contaminants, PCB metabolites or the
PCBs themselves."
The study measured the levels of PCBs in blood taken from
pregnant women during a San Francisco Bay Area study in the 1960s. The
researchers then compared the PCB levels in the women's blood with the
genders of their children. It found that, for every microgram of PCBs per
liter of serum, the chances of having a male child fell by seven percent.
"The women most exposed to PCBs were 33 percent less
likely to give birth to male children than the women least exposed,"
Hertz-Picciotto said.
PCBs are a group of pollutants widely used in industry as
cooling and insulating fluids until they were banned in the 1970s over
concerns about their toxicity and accumulation in the environment. They are
still ubiquitous in the environment and have been associated with adverse
effects on immune, reproductive, nervous and endocrine systems in people and
animals.
Hertz-Picciotto says that the study is also important
because it will help assess the health risks of populations currently
exposed to high levels of PCBs, like those that consume fish from
contaminated lakes or that live near former manufacturing facilities.
Other chemicals with molecular structures that are similar
to those of PCBs, like the flame retardants PBDEs (polybrominated diphenyl
ethers), are widely used in plastic casings of televisions, computers and
other electronics, and in foam products and textiles.
"PBDEs share many of the biochemical and toxicologic
properties of PCBs," Hertz-Picciotto said. "As the levels of these
substances rise in wildlife and human populations, studies like ours provide
an indication of the potential effects of these newer compounds."
Funding for the study was provided by grants from the
National Institutes of Health (NIH), the National Institute of Environmental
Health Sciences (NIEHS), the National Cancer Institute (NCI) and the
National Institute of Child Health and Human Development (NICHD).
