Fine particulate air pollution may be linked to an increased risk of developing childhood autism, according to a new study.

At least, that's if exposure occurs during pregnancy through the first two years of a child's life, University of Pittsburgh researchers reported in the journal Environmental Research.

Autism spectrum disorder (ASD) is a condition that affects one in 68 children, with reported cases having risen nearly eight-fold in the last two decades. While a wealth of evidence has refuted the claim that vaccines can lead to childhood autism, now it appears that air pollution may play a small role.

"Autism spectrum disorders are lifelong conditions for which there is no cure and limited treatment options, so there is an urgent need to identify any risk factors that we could mitigate, such as pollution," lead study author Evelyn Talbott said in a press release. "Our findings reflect an association, but do not prove causality. Further investigation is needed to determine possible biological mechanisms for such an association."

Talbott and her colleagues studied the families of 211 children with ASD and 219 children without ASD born between 2005 and 2009. They took into account where the mothers lived before, during and after pregnancy, and thus were able to estimate individual exposure to a type of air pollution called PM2.5.

This type of pollution refers to particles found in the air that are less than 2.5 micrometers in diameter, or 1/30th the average width of a human hair. PM2.5 includes dust, dirt, soot and smoke. And because of its small size, PM2.5 can reach deeply into the lungs and get into the blood stream.

Based on the child's exposure to concentrations of PM2.5 during the mother's pregnancy and the first two years of life, the research team found that children who were more exposed to particulate air pollution had roughly a 1.5-fold greater risk of developing ASD.

This study isn't the first to suggest a link between PM2.5 and autism. In addition, previous research has revealed an association between ASD and increased levels of air toxics, including chromium and styrene.

"Air pollution levels have been declining since the 1990s; however, we know that pockets of increased levels of air pollution remain throughout our region and other areas," said Talbott. "Our study builds on previous work in other regions showing that pollution exposures may be involved in ASD. Going forward, I would like to see studies that explore the biological mechanisms that may underlie this association."

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