Air pollution exposure in early life linked to autism

By Sally Robertson, B.Sc.Nov 29 2012

Exposure to air pollution in early life or during pregnancy puts children at risk for autism, show study findings.

Children exposed to high levels of traffic-related air pollution were more likely to develop autism than those exposed to low levels, report Heather Volk (University of Southern California, Los Angeles, USA) and colleagues.

Similarly, exposure during this time to high levels of regional particulate matter less than 2.5 µm (PM_2.5) and 10 µm (PM₁₀) in diameter was also associated with risk for autism.

"Our study draws on a rich record of residential locations of children with typical development and children with autism across California, allowing us to assign modeled pollutant exposures for developmentally relevant time points," says the team.

Using birth certificates and residential history questionnaires, the team established the addresses of 524 children (aged 24-60 months when enrolled) during each trimester of their mother's pregnancy and for their first year of life. The California Line Source Dispersion Model was then used to estimate locally varying ambient concentrations of nitrogen oxides contributed by freeways, nonfreeways, and all roads located within 5 km of each child's home.

Other traffic-related pollutants including elemental carbon and carbon monoxide are almost perfectly correlated with estimates for nitrogen oxides, explain Volk et al. "Thus, our model-based concentrations should be viewed as an indicator of the traffic-related pollutant mixture rather than of any pollutant specifically."

The US Environmental Protection Agency's Air Quality System data were used to assess exposure to PM_2.5, PM₁₀, and nitrogen dioxide.

As reported in the Archives of General Psychiatry, children living in homes with the highest levels (31.8 parts per billion [ppb]) of traffic-related air pollution were significantly more likely to have autism than those from homes with the lowest levels (9.7 ppb or less), at an odds ratio of 3.1, after adjustment for age, gender, and demographic and socioeconomic variables.

Highest versus lowest levels of traffic-related air pollutant exposures during pregnancy were also significantly associated with autism risk during all three trimesters.

Similarly, the highest versus lowest levels of exposure to PM_2.5, PM₁₀, and nitrogen dioxide during gestation or the first year of life were associated with a significantly increased risk for autism among the children, with the smallest effects present in the first trimester for each pollutant.

"Diesel exhaust particles and polycyclic aromatic hydrocarbons (commonly present in diesel exhaust particles) have been shown to affect brain function and activity in toxicological studies," note the researchers.

"The public health implications of these findings are large because air pollution exposure is common and may have lasting neurological effects," concludes the team.

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