The study in California involved more than 500 children, finding those who were exposed to high levels of pollution were three times more likely to be autistic than children living in the cleanest air measured.
But experts have called the findings ‘very unlikely’ to show a causal link and remain unconvinced.
The Autism spectrum covers a range of social interaction disorders, including Asperger’s syndrome, that vary from mild to severe and are typified by problems with social skills and communication. Experts have questioned how pollutants change the brain’s development.
The study compared 279 children with autism and 245 without with the levels of pollution they were exposed to in the womb and during the first year of their lives. It concluded that children whose homes were exposed to the highest levels of pollution had a three times higher risk of having autism than those with the lowest.
Uta Frith, professor of cognitive development at University College London (UCL) said: "It seems to me very unlikely that the association is causal."
She added: “The study does not get us any further since it does not present a convincing mechanism by which pollutants could affect the developing brain to result in autism.”
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The study does not factor in other risk factors for autism, such as family history, and rather than being able to claim traffic pollution causes autism, it merely suggests there is a link of some kind.
Sophia Xiang Sun, from the University of Cambridge's autism research centre, said regardless of the study, cutting pollution would be beneficial to our general health.
"We know that traffic-related air pollution can contribute to many other diseases and conditions, and it is biologically plausible it also has a role in pathways of autism.
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"However, whether or not the potential association between autism and traffic-related air pollution exists, reduction of traffic-related air pollution would be good for public health."