Exposure to routine agricultural pesticides before birth and during the
first year of life is linked to increased
risk of autism spectrum disorder (ASD) compared with infants of women
with no such exposure, according to a study published in The BMJ.
The researchers say their findings support efforts to prevent
exposure to pesticides during pregnancy to protect a child's developing
‘Pregnant women are advised to avoid common agricultural pesticide exposure to protect developing baby's brain from autism and intellectual disability.’
Experimental studies have suggested that common pesticides can
affect normal brain development, and environmental exposures during
early brain development are suspected to increase risk for autism
spectrum disorders in children.
But studies examining pesticide exposure in the real world and risk of ASD are rare.
So researchers at the University of California used registry records
to identify 2,961 patients with a diagnosis of ASD - including 445 with
ASD with accompanying intellectual disability - and 35,370 healthy
("control") patients of the same birth year and sex.
Participants were born between 1998 and 2010 in California's Central
Valley, a heavily agricultural region, and 80% of cases were male.
Data from the California state-mandated Pesticide Use Registry were
then integrated into a geographic information system tool to assess
prenatal (before birth) and infant exposures to 11 commonly used
pesticides (measured as pounds of pesticides applied per acre/month
within 2 km of their mother's residence during pregnancy and exposure
during developmental periods defined as yes vs no).
These pesticides were selected because of their high use and evidence indicating toxic effects on brain development.
After adjusting for potentially influential factors, the researchers
found modest increases in ASD risk among offspring exposed to several
pesticides (including glyphosate, chlorpyrifos, diazinon, malathion,
permethrin, bifenthrin and methyl-bromide) before birth and during the
first year of life, compared with controls.
Associations were strongest in those with ASD and intellectual
disability, which represents the more severe end of the autism spectrum.
This is an observational study, and as such, can't establish cause,
and the researchers point to some limitations, such as relying on
patient records for details about diagnoses, and being unable to examine
Nevertheless, they say their study is by far the largest
investigating pesticides and autism spectrum disorder to date and their
findings back up earlier work in this field.
"Our findings suggest that ASD risk may increase with prenatal and
infant exposure to several common ambient pesticides that impacted
neurodevelopment in experimental studies," they write.
They call for further research to explore underlying mechanisms in
the development of autism. However, from a public health and preventive
medicine perspective, they say their findings "support the need to avoid
prenatal and infant exposure to pesticides to protect the developing
In a linked editorial, Amanda Bakian and James VanDerSlice at the
University of Utah agree that reducing exposure to pesticides during
pregnancy "is sensible public health policy" but they point out that
this "might be close to impossible for some populations."
Future research exploring underlying biological mechanisms and
individual susceptibilities in other regions of the world "may help to
translate these study findings into more refined public health actions
for pregnant women residing in areas of high pesticide use," they