Autism and Air Pollution

New findings suggest a mother’s exposure to traffic pollution might be a contributing factor to autism.

2015 UWM Research Report
February 2015

Autism isn’t caused by vaccines. It’s not contagious. There is certainly a genetic component to it. About its origins, epidemiologist Amy Kalkbrenner has this to add: “There is something about traffic-related air pollution that can be linked to autism rates. We’re not sure what exactly, but the latest research shows we’re on to something.”

Kalkbrenner’s landmark study, just published in the journal Epidemiology, showed that air pollution’s impact on autism rates in North Carolina is similar to results of pollution-autism studies in California – despite weather and climate differences between the two states.

These findings build on previous studies that have shed light on the origins of the world’s fastest growing developmental disorder. Kalkbrenner and her colleagues found that exposure to higher amounts of traffic-related air pollution might do the most damage to unborn children in the third trimester of pregnancy.

“This supports the hypothesis that environmental chemicals are part of the autism puzzle,” says Kalkbrenner, who is an assistant professor in UW-Milwaukee’s Joseph J. Zilber School of Public Health.

Kalkbrenner’s study zeroed in on PM10, airborne coarse and fine particulate matter that arises in part from traffic-related air pollution. A research team of eight evaluated mounds of medical records, covering pre-conception through the first birthday for 87,000 children in North Carolina and 77,500 in California born in the mid- to late 1990s. Key regions in each state were selected based on the team’s ability to simultaneously measure the level of particulate matter present and know which children had autism in these regions.

Researchers used a new, more exact tool to measure the levels of particulate matter in smaller slices of time, based on pollution at the family’s address during pregnancy. With this method, they were able to compare exposures during specific weeks of pregnancy. Approximately 1,000 children who later developed some form of autism spectrum disorder were then compared to all other children.

Better measurement tools and the two-state comparison are what make this study more likely valuable, Kalkbrenner says. Evidence for a link between a chemical exposure and a health impact like autism is more likely when it can be shown in more than one region.

“We’ve now had three solid studies saying the same thing. The evidence is pretty compelling that something is going on with air pollution and autism,” says Kalkbrenner.

“Our findings of greater susceptibility in the third trimester are consistent with other studies that demonstrate links between autism and altered brain network development, specifically synaptic connections that develop during the final months of pregnancy.”

Future research will dig deeper into the chemical components if the autism-pollution connection. What chemicals are most dangerous? When is their impact strongest?