By Paul D. Thacker, Science News
Despite research on rats that shows the placenta
can block certain combustion-related pollutants, researchers have
found that a marker of secondhand cigarette smoke accumulates
at greater levels in the plasma of fetuses than that in mothers.
They also discovered that cancer-causing benzo[a]pyrene (BP) has
more harmful effects on fetal than on maternal DNA. This study
bolstered previous findings in Poland, where women were exposed
to secondhand smoke and levels of BP that were 30 times higher.
Corresponding author Frederica P. Perera, director
of the Columbia Center of Children’s Environmental Health
at Columbia University, says the results are a concern, because
exposure to BP has been linked to DNA damage and increased risk
“This study demonstrates that the fetus is
more susceptible to DNA damage from combustion-related pollutants
than previously thought,” says Perera.
Researchers from the Columbia Center and the Center
for Disease Control and Prevention tracked 265 nonsmoking mothers
and their newborns in New York City. The mothers are exposed to
significant air pollution in their neighborhood, where the average
ambient BP concentration was less than 0.5 nanograms per cubic
meter of air. Perera says higher levels can be found in California
and many European cities. This study was published in the July
issue of Environmental Health Perspectives (Environ. Health Perspect.
2004, 12, 1133–1136).
The researchers found that 45% of newborns had
detectable BP-DNA adducts, as did 41% of mothers. The levels of
adduct formation were similar in mother and child: 0.24 adducts
per 100 milllion nucleotides in mothers and 0.22 adducts per 100
million nucleotides in newborns.
Cotinine, a metabolite of nicotine, was detected
in the serum of 47% of newborns and 44% of mothers. The levels
were also quite similar, at 1.7 nanograms per milliliter (ng/mL)
in newborns versus 1.28 ng/mL in mothers. The higher levels of
cotinine in newborns indicate that the effects of environmental
tobacco smoke are only slowly cleared from the fetuses’
Previous research on the same cohort of New Yorkers
found that elevated levels of BP-DNA adducts in combination with
secondhand smoke correlated with poor birth outcomes, including
smaller head circumference and lower birth weight.
“We know that there is a lot of smoking in
these neighborhoods, but you would think that with nonsmoking
mothers that these babies would be protected,” says Ellen
F. Crain, professor of pediatrics at the Albert Einstein College
of Medicine. “What I find interesting about this study is
that we’re finally starting to look for a mechanism for
some of the outcomes we find clinically.”