[ 2011-04-21 ]

Pesticide exposure in womb may hurt child's IQ
Children whose mothers are exposed to high amounts
of certain pesticides while pregnant appear to
have lower IQs than their peers when they reach
school age, according to three government-funded
studies.

The pesticides, known as organophosphates, are
commonly sprayed on food crops and can be found in
trace amounts on berries, green beans, and other
fruits and vegetables sold in stores. The
pesticides have also been used in homes and
gardens, although their indoor use has been widely
restricted due to safety concerns.

Organophosphates, which kill pests by attacking
the nervous system, have previously been linked to
developmental delays and attention problems in
young children who were exposed in the womb. Now,
researchers in two different locations have found
that a child's IQ tends to decrease in proportion
to the mother's exposure while pregnant.

One of the studies followed hundreds of mostly
Latino mothers and children in California's
Salinas Valley, a center of commercial
agriculture. Many of the women were farmworkers,
or had family members who worked on farms.

When the women were pregnant, the researchers
tested their urine for several chemical
by-products of organophosphates -- a standard
means of gauging exposure. The mothers with the
highest levels of by-products, known as
metabolites, had children whose IQs at age 7 were
seven points lower, on average, than the children
whose mothers had the lowest levels of exposure.
(The average score is 100.)

"That's not unlike the decreases we see in
children with high lead exposure," says the senior
study author, Brenda Eskenazi, Ph.D., a professor
of epidemiology and maternal and child health at
the University of California, Berkeley. "It's
equivalent to performing six months behind the
average."

The children's own metabolite levels were not
linked to their IQs, however, which suggests that
prenatal -- rather than childhood -- exposure is
largely responsible for the trend, Eskenazi says.
Organophosphates, which pass from the mother to
fetus through the placenta and umbilical cord, may
be more damaging to developing fetuses than to
children, the study notes.

Similar trends are likely to be found outside
farming communities, the researchers suggest.
While the average metabolite levels of the
pregnant women in the study were substantially
higher than the national average, as many as 25%
of pregnant women in the general population have
levels above the study average.

Moreover, the findings are echoed by a second
study which was conducted in New York City and
followed 265 black and Dominican mothers and
children from low-income families.

In that study, researchers measured levels of the
organophosphate chlorpyrifos in the women's
umbilical cord blood. Chlorpyrifos, which has
since been banned for indoor use, was still
commonly used as a residential pesticide when the
women were pregnant.

Using the same IQ test as the California study,
the researchers found that when the children were
7, the IQs of those with the highest exposure in
the womb was roughly three points lower, on
average, than those with the lowest prenatal
exposure.

The joint findings are strengthened by the
differences in the locations, study participants,
and methods used to measure pesticide exposure,
says Bruce Lanphear, M.D., a professor of health
sciences at Simon Fraser University, in Vancouver,
British Columbia. "Because the results are so
consistent, we're more confident that the results
are not spurious," says Lanphear, who was not
involved in the research.

In both studies, the researchers sought to cancel
out other factors that can affect a child's IQ.
They controlled for the mother's education and
income, and observed the stimulation provided by
the child's home environment. The California study
also factored in the mother's exposure to lead and
toxic flame retardants.

Experts aren't sure how organophosphates might
interfere with fetal brain development, although
they do know that in insects the pesticides slow
the breakdown of acetylcholine, an important
neurotransmitter.

"There have been a lot of studies that indicate
that there are probably other mechanisms," says
the senior author of the New York City study,
Robin Whyatt, DrPH, a professor of clinical
environmental health sciences at Columbia
University's Mailman School of Public Health.

Genes may play a role, in fact. In the third
study, which also looked at children in New York
City, researchers found that the association
between organophosphate exposure and developmental
delays was more pronounced in children whose
mothers had a certain genetic variant that
influences an enzyme that breaks down
organophosphates.

The three studies appear in the April 21 issue of
the journal Environmental Health Perspectives. All
three were funded by grants from the Environmental
Protection Agency and the National Institute of
Environmental Health Sciences, among other
sources.

The average exposure to organophosphates is lower
today than it was when these studies began a
decade ago. Now that the indoor use of
organophosphates has been all but eliminated, the
main sources are direct exposure to commercial
agriculture and the traces found on supermarket
produce.

Eskenazi stresses, however, that pregnant women
should not stop eating fruits and vegetables.
"It's absolutely important that they have an
adequate diet in terms of the health of their
child," she says.

Still, she adds, "It's important that people wash
their fruits and vegetables really, really well --
and that means even fruit with a peel on it. It
should be washed before you peel it."

Source - health.com

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