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Air pollution raises autism risk

by Christian Nordqvist

Pregnant women exposed to high levels of air pollution are twice as likely to have a child with autism compared to women exposed to low levels, scientists from Harvard School of Public Health (HSPH) reported in Environmental Health Perspectives (June 18th edition)

The authors claim that theirs is the first large nationwide study to examine associations between air pollution and ASD (autism spectrum disorder) rates across the United States.

Lead author Andrea Roberts, a research associate in the HSPH Department of Social and Behavioral Sciences, said: 

"Our findings raise concerns since, depending on the pollutant, 20% to 60% of the women in our study lived in areas where risk of autism was elevated."

Previous studies have shown how methylene chloride, lead, mercury, manganese, diesel and other particulates found in polluted air can affect the physical and neurologic development of the fetus and baby.

Two studies have already demonstrated a link between air pollution exposure during pregnancy and ASD risk. However, they only examined three locations in the country.

Roberts and colleagues gathered and examined data from the Nurses' Health Study II, which began in 1989 and included details on 116,430 nurses. They focused on data on 325 women who gave birth to a child who was eventually diagnosed with an autism spectrum disorder and 22,000 others whose children did not have the disorder.

The team analyzed environmental data from the EPA (US Environmental Protection Agency) to estimate how much air pollution the mothers were exposed to while pregnant. They also factored in some possible confounders, such as smoking during pregnancy, education and income. The main aim was to look at links between autism spectrum disorders and pollution levels at the time and place of birth.

Diesel and mercury levels linked to autism risk in offspring

The authors found that the 
pregnant mothers living in the 20% of areas with the most air pollution had twice the risk of having a child with autism, compared to those living in the 20% of locations with the lowest levels. The researchers focused on levels of diesel particulates and/or mercury in the air.

Methylene chloride, manganese and lead also raised autism risk

Regarding other pollutants, such as lead, methylene chloride, manganese, and combined metal exposure, a 50% higher risk of autism in offspring was found among those who had been living in areas with the highest levels during their pregnancy, compared to those with the least exposure.