A study by the University of Southern California has found a
link between autism and pesticides.
The study does not prove that pesticides cause autism, but
does show that autism rates are higher where there are more pesticides used.
Pregnant women who
lived close to fields and farms where chemical pesticides were applied
experienced a two-thirds increased risk of having a child with autism spectrum
disorder or other developmental delay, the researchers say.
The associations
were stronger when the exposures occurred during the second and third trimesters
of the women’s pregnancies.
The large,
multisite California-based study examined associations between specific classes
of pesticides, including organophosphates, pyrethroids and carbamates, applied
during the study participants’ pregnancies and later diagnoses of autism and
developmental delay in their offspring. It is published online today in
Environmental Health Perspectives.
“This study
validates the results of earlier research that has reported associations
between having a child with autism and prenatal exposure to agricultural
chemicals in California,” said lead study author Janie F. Shelton, a University
of California at Davis graduate student who now consults with the United
Nations.
“While we still must investigate whether certain sub-groups are more
vulnerable to exposures to these compounds than others, the message is very
clear: Women who are pregnant should take special care to avoid contact with
agricultural chemicals whenever possible,” she said.
The study was
conducted by examining commercial pesticide application using the California
Pesticide Use Report and linking the data to the residential addresses of
approximately 1,000 participants in the Northern California-based Childhood
Risk of Autism from Genetics and the Environment (CHARGE) Study. The study
includes families with children between two and five diagnosed with autism or
developmental delay or with typical development.
It is led by
principal investigator Irva Hertz-Picciotto, a MIND Institute researcher and
professor and vice chair of the Department of Public Health Sciences at UC
Davis.
The majority of
study participants live in the Sacramento Valley, Central Valley and the
greater San Francisco Bay Area.
Twenty-one chemical
compounds were identified in the organophosphate class, including chlorpyrifos,
acephate and diazinon.
The second most
commonly applied class of pesticides was pyrethroids, one quarter of which was
esfenvalerate, followed by lambda-cyhalothrin permethrin, cypermethrin and
tau-fluvalinate.
Eighty percent of
the carbamates were methomyl and carbaryl.
For the study,
researchers used questionnaires to obtain study participants' residential
addresses during the pre-conception and pregnancy periods. The addresses then
were overlaid on maps with the locations of agricultural chemical application
sites based on the pesticide-use reports to determine residential proximity.
The study also examined which participants were exposed to which agricultural
chemicals.
“We mapped where
our study participants’ lived during pregnancy and around the time of birth.
“In California,
pesticide applicators must report what they’re applying, where they’re applying
it, dates when the applications were made and how much was applied,”
Hertz-Picciotto said.
“What we saw were
several classes of pesticides more commonly applied near residences of mothers
whose children developed autism or had delayed cognitive or other skills.”
