DDT
linked to an increase in autism risk in new study
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| Will Trump act on his notorious need for revenge to bring DDT back on the market. DDT nearly wiped out the bald eagle. |
The discontinued
pesticide DDT is linked to an increased risk of autism, according to a new
study out of Columbia University Medical Center.
The study, published
today in the American Journal of Psychiatry, found that a mother's
exposure to DDT increased the risk of her child developing autism spectrum
disorder.
The study builds on
previous evidence that the environmental toxic is linked to developmental
impacts in children exposed in utero, and is significant as autism rates keep
growing in the U.S. and researchers don't yet know what causes the
disorder. Approximately one in 59 kids in the
U.S. has autism—up from one in 150 in the year 2000.
DDT was an insecticide heavily used in
the 1940s to 1960s but banned in 1972 in the US because of its impact on
wildlife and concerns over its effect on fertility, immune systems, hormones
and brain development.
The chemical takes a while to break down and accumulates in fatty tissue, so even though it has been banned for decades, people are still exposed through food—mostly seafood, Kristen Lyall, professor at the Drexel Autism Institute at Drexel University, told EHN. Lyall was not involved in the new study.
In the study,
researchers matched 778 cases of childhood autism with maternal blood samples
in Finland. The mothers' blood samples were tested for DDE, a metabolized form
of DDT, and for another banned toxic—polychlorinated biphenyls (PCBs). Women
with the highest levels of exposure to DDE were 32 percent more likely to have
a child with autism.
The association between
the increased risk and higher maternal exposure of DDE was significant for boys
but not girls. Autism is about 4 times more common in US boys, according to
federal data.
There was no link
between PCB exposure and autism rates.
Why the link?
It's not clear why DDE
increases the risk of autism but the researchers suggested two reasons.
The first is because
maternal exposure to DDT has previously been linked with premature birth and
smaller children—both risks for later developing autism.
The second reason is
that DDE has an effect on androgens, which are male sex hormones. DDE exposure
has been shown to cause problems with androgens' abilities to bind to their
receptors, Dr. Alan Brown, lead author of the new study and a professor of
psychiatry and epidemiology at Columbia University Medical Center, told EHN.
Like Brown, Lyall has
also looked at DDT and PCBs and autism risks, but her study, which was
published in 2017 in Environmental Health
Perspectives, found opposite results to Brown's. In her study,
it was the PCBs, not DDT, that were linked to an increase in autism.
Both Brown and Lyall are
quick to point out that both studies need to be repeated and neither
definitively means the chemicals caused the disorders.
Brown also pointed out
the differences between Lyall's study and his. Brown's studied women and
children in Finland and had a much larger population than Lyall's population,
which was based in California, he said. The differences in population may
attribute to the disparate findings, he said.
"It tells us about
the importance about studying different populations, and then to home in on
what might be different about this population to tell us even more about
autism," Brown said.
Brown said the lingering
legacy from DDT and PCBs should serve as cautionary tales for other compounds.