Prenatal Exposure to Air Pollution Linked to Autism Risk

Pregnant women exposed to high levels of air pollution while pregnant are twice as likely to have a child with autism when compared to women in areas with low pollution, a new study from Harvard School of Public Health (HSPH) found.

The study, published in the journal Environmental Health Perspectives, is the first large national study to examine the link between the two and included data from Nurses' Health Study II, a long-term study based at Brigham and Women's Hospital involving 116,430 nurses beginning in 1989.

From the group, the authors studied 325 women who had a child with autism and 22,000 women whose child did not have the disorder.

They then looked at associations between autism and levels of pollutants at the time and place of birth using air pollution data from the U.S. Environmental Protection Agency to estimate the mothers' level of exposure at the time of pregnancy.

After adjusting for factors such as income, education and smoking during pregnancy, the results showed that women who lived in 20 percent of locations with the highest levels of diesel particulates or mercury in the air were twice as likely to have a child with autism than those who lived in the 20 percent of areas with the lowest levels.

This was true for other kinds of pollution as well, including lead, manganese, methylene choride and combined metal exposure. And while most pollutants were associated with autism more strongly in boys than girls, the authors said this finding should be further examined as there were few girls with autism in the study.

"Our findings raise concerns since, depending on the pollutant, 20 percent  to 60 percent of the women in our study lived in areas where risk of autism was elevated," Andrea Roberts, lead author and research associate at the USPH department of social and behavioral sciences, said in a press release.

The results, while significant, are not altogether surprising as exposure to diesel particulates, lead, manganese, mercury, methylene chloride and other pollutants are known to affect brain function and a developing baby.

Furthermore, two previous studies found associations between air pollution during pregnancy and autism in children, but those studies looked at data from just three locations in the United States.

Senior author Marc Wesskopf, associate professor of environmental and occupational epidemiology at HSPH, argues the study's findings should act as an impetus to other researchers to examine the subject.

"Our results suggest that new studies should begin the process of measuring metals and other pollutants in the blood of pregnant women or newborn children to provide stronger evidence that specific pollutants increase the risk of autism," he said. "A better understanding of this can help to develop interventions to reduce pregnant women's exposure to these pollutants."