Exposure to traffic-related pollution during pregnancy and a child's first year of life appears to be associated with an elevated risk of autism, scientists found in an analysis released Monday.

Medical investigators, reporting in the Archives of General Psychiatry, found that children living in homes near the highest levels of traffic-related air pollution were three times as likely to have an autism spectrum disorder as children living in homes with the lowest exposures.

The key pollutants, researchers found, were vehicle-related particulate matter and nitrogen dioxide, a leading precursor of ozone, also known as smog.

Dr. Heather Volk of the University of Southern California based her conclusions on both a scientific model, which calculated proximity to major traffic thoroughfares, and federal air pollutant measures.

The ubiquity of fossil-fuel-powered motor vehicles, she and her team said, makes the link between high traffic and autism a genuine concern.

Volk's investigation is part of an emerging body of research probing a variety of environmental exposures that may play a role in the distinct disorders falling under the autism rubric.

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Researchers studied 279 children with an autism spectrum disorder and a control group of 245 youngsters who were autism-free. The team used mothers' addresses to estimate the particulate matter and nitrogen dioxide exposure during each trimester of pregnancy and for a child's first year of life.

Volk suggests her work may lead to "the identification of the biologic pathways that are activated in autism and to improved prevention and therapeutic strategies."

Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at the Steven and Alexandra Cohen Children's Medical Center in New Hyde Park, said the research, while compelling, will have to be replicated to decidedly confirm an association between pollutants and autism.

"Although this study provides further support for the notion that exposure to traffic-related air pollutants is a risk factor for autism, most children with autism do not live near highways.

"Undoubtedly, autism has many different causes and risk factors -- and only some of these are known at this time," Adesman said.

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Michael Seilback of the American Lung Association said Nassau and Suffolk both received grades of B on particulate matter in his organization's most recent State of the Air Report.

However, Suffolk received an F for high ozone levels. Seilback noted a grade could not be given to Nassau on ozone concentrations because the county has no monitor.

"Also, there's a caveat to those B grades," Seilback said. "There are areas across Long Island that may have higher levels [of particulate matter], especially near major thoroughfares where there's a lot of truck and diesel pollution."

Particulate matter tends to remain concentrated in areas where it's deposited; ozone travels, Seilback said.

Volk's study, meanwhile, isn't the first this year to show the deleterious effect of traffic pollutants on the brain. A study in February demonstrated declines in memory and a loss of attention span in older women.