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 The greater the exposure to fine particulates emitted by fires,
vehicles, and industrial smokestacks the greater the risk, found the
study, published online in Environmental Health Perspectives.
Earlier research also found an autism-pollution connection,
including a 2010 study that found the risk of autism doubled if a
mother, during her third trimester, lived near a freeway, a proxy
for exposure to particulates. But this is the first to examine the
link across the United States, and "provides additional support" to
a possible link, said Heather Volk of the University of Southern
California Children's Hospital, who led earlier studies.
U.S. diagnoses of autism soared to one in 68 children in 2010 (the
most recent data) from one in 150 in 2000, government scientists
reported in March. Experts are divided on how much of the increase
reflects greater awareness and how much truly greater incidence.
Although the disorder has a strong genetic basis, the increasing
incidence has spurred scientists to investigate environmental
causes, too, since genes do not change quickly enough to explain the
rise.
The Harvard study included children of the 116,430 women in the
Nurses' Health Study II, which began in 1989. The researchers
collected data on where the women lived while pregnant and levels of
particulate pollution. They then compared the prenatal histories of
245 children with autism spectrum disorder to 1,522
normally-developing children, all born from 1990 to 2002.
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There was no association between autism and fine particulate
pollution before or early in pregnancy, or after the child was born.
But high levels of exposure during the third trimester doubled the
risk of autism.
Evidence that a mother-to-be's exposure to air pollution affects her
child's risk of autism "is becoming quite strong," said Harvard
epidemiologist Marc Weisskopf, who led the study, suggesting a way
to reduce the risk.
It is not clear how tiny particles might cause autism, but they are
covered with myriad contaminants and penetrate cells, which can
disrupt brain development.
Last year the Environmental Protection Agency, citing the link to
asthma, lung cancer and cardiovascular disease, tightened air
quality standards for fine particulate pollution. States have until
2020 to meet the new standards.
(Reporting by Sharon Begley; editing by Andrew Hay)
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