Pesticide link to autism suspected
A state study suggests two farm sprays may raise chances of having a child with the disorder.
By Marla Cone
Times Staff Writer
July 30, 2007
Women who live near California farm fields sprayed with organochlorine
pesticides may be more likely to give birth to children with autism,
according to a study by state health officials to be published today.
rate of autism among the children of 29 women who lived near the fields
was extremely high, suggesting that exposure to the insecticides in the
womb might have played a role. The study is the first to report a link
between pesticides and the neurological disorder, which affects one in
every 150 children.
But the state scientists cautioned that
their finding is highly preliminary because of the small number of
women and children involved and lack of evidence from other studies.
"We want to emphasize that this is exploratory research," said Dr. Mark
Horton, director of the California Department of Public Health. "We
have found very preliminary data that there may be an association. We
are in no way concluding that there is a causal relationship between
pesticide exposure of pregnant women and autism."
pesticides implicated are older-generation compounds developed in the
1950s and used to kill mites, primarily on cotton as well as some
vegetables and other crops. Their volumes have declined substantially
in recent years.
Examining three years of birth records and
pesticide data, scientists from the Public Health Department determined
that the Central Valley women lived within 500 meters, or 547 yards, of
fields sprayed with organochlorine pesticides during their first
trimester of pregnancy. Eight of them, or 28%, had children with
autism. Their rate of autism was six times greater than for mothers who
did not live near the fields, the study said.
senior scientist of Pesticide Action Network North America, a San
Francisco-based advocacy group, said the report adds to an existing
body of evidence that endosulfan and dicofol, already banned in some
countries, are harmful.
"This is one of the first papers that
links use of pesticide to incidence of a disease, and autism in
particular," she said. "The findings are very strong. This is a sixfold
risk factor in comparison to someone who is not exposed. There aren't
too many studies that come out like that."
Even though small
numbers of children were involved, "it is still one of those things
that make you sit up and pay attention," she said.
suggest that 7% of autism cases in the Central Valley during the years
studied — 1996 through 1998 — might have been connected to exposure to
the insecticides drifting off fields into residential areas. Births
during those years were analyzed because children born later might not
yet be diagnosed with autism.
Children with autism spectrum
disorders have impaired social and communication skills. The causes are
unknown, but because diagnoses have been increasing, scientists have
been exploring various environmental factors, including children's
vaccines and chemical pollutants.
"The good news is we've used
a new research technology to generate hypotheses and possible
associations, so we are making progress in the battle to get more
information" about the cause of autism, Horton said.
The goal of
the study was to "systematically explore the general hypothesis that
residential proximity to agricultural pesticide applications during
pregnancy could be associated with autism spectrum disorders in
offspring," the authors wrote in their study, published online today in
the scientific journal Environmental Health Perspectives.
scientists collected records of nearly 300,000 children born in the 19
counties of the Sacramento and San Joaquin river valleys. Of those
children, 465 had autism. The scientists then compared the addresses
during pregnancy to state records that detailed the location of fields
sprayed with several hundred pesticides.
For most pesticides, no
unusual numbers of autism cases were found, but the exception was a
class of compounds called organochlorines. Most, including DDT, were
banned in the United States several decades ago because they were
building up in the environment. Only dicofol and endosulfan remain.
The autism rate was highest for children of those mothers who lived the
closest to the fields and it declined as the distance from the fields
There is no other human or animal evidence that the
two chemicals can cause autism. But both affect nerves and the brain —
and cause reproductive effects and alter hormones in animal tests. In
addition, dicofol is a possible human carcinogen.
scientists concluded that "the possibility of a connection between
gestational exposure to organochlorine pesticides and autism spectrum
disorders requires further study."
A July report by the state
Department of Pesticide Regulation said endosulfan can spread far from
fields via the air and expose the public, based on air monitoring in
Fresno, Monterey and Tulare counties. The agency is likely to designate
endosulfan as a toxic air contaminant soon, and dicofol could follow.
That designation triggers a review by the agency to see whether steps
should be taken to minimize the chemicals drifting off fields into
Glenn Brank, spokesman for the pesticide
agency, said officials there are "very interested" in the new autism
data but say that "more work" on the potential link is needed before it
can carry much weight in assessments of the chemicals' risks.
two insecticides are now used much less often than in the years in
which the possible connection to autism was found. As a result, there
is less likelihood that pregnant women are exposed today. Nearly
774,000 pounds were applied in 1996, compared with 277,000 pounds in
2005, down nearly 64%, according to state records.
"In the past couple years, the bottom has dropped out of these two," Brank said.
Insects have built up resistance and cotton farmers have switched to new compounds.
The two chemicals are not found in household or yard pesticides. Traces
are found in food, but the study looked only at possible exposure from
the air. The chemicals are used most extensively in Fresno, Kings,
Imperial and Tulare counties. Dicofol is mostly used on cotton,
oranges, beans and walnuts. Endosulfan is used primarily in tomato
processing and on lettuce, alfalfa and cotton crops.
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