Volume 44, Issue 10, November 2014, Pages 277–318
Environmental Chemical Exposures and Autism Spectrum Disorders: A Review of the Epidemiological Evidence
Environmental Chemical Exposures and Autism Spectrum Disorders: A Review of the Epidemiological Evidence
- Available online 5 September 2014
In
the past decade, the number of epidemiological publications addressing
environmental chemical exposures and autism has grown tremendously.
These studies are important because it is now understood that
environmental factors play a larger role in causing autism than
previously thought and because they address modifiable risk factors that
may open up avenues for the primary prevention of the disability
associated with autism. In this review, we covered studies of autism and
estimates of exposure to tobacco, air pollutants, volatile organic
compounds and solvents, metals (from air, occupation, diet, dental
amalgams, and thimerosal-containing vaccines), pesticides, and organic
endocrine-disrupting compounds such as flame retardants, non-stick
chemicals, phthalates, and bisphenol A. We included studies that had
individual-level data on autism, exposure measures pertaining to
pregnancy or the 1st year of life, valid comparison groups, control for
confounders, and adequate sample sizes. Despite the inherent error in
the measurement of many of these environmental exposures, which is
likely to attenuate observed associations, some environmental exposures
showed associations with autism, especially traffic-related air
pollutants, some metals, and several pesticides, with suggestive trends
for some volatile organic compounds (e.g., methylene chloride,
trichloroethylene, and styrene) and phthalates. Whether any of these
play a causal role requires further study. Given the limited scope of
these publications, other environmental chemicals cannot be ruled out,
but have not yet been adequately studied. Future research that addresses
these and additional environmental chemicals, including their most
common routes of exposures, with accurate exposure measurement
pertaining to several developmental windows, is essential to guide
efforts for the prevention of the neurodevelopmental damage that
manifests in autism symptoms.
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