Exposure to high levels of air pollutants has been linked to autism spectrum disorder (ASD) in children, according to the first national study performed on the topic, and published today by Environmental Health Perspectives (EHP). The study concludes that “perinatal exposure to air pollutants,” such as diesel, lead, manganese, mercury, methylene chloride, and other industrial byproduct pollutants, “may increase risk for ASD.”

Researchers considered associations between EPA data about levels of hazardous air pollutants and the time and place of birth, and ASD in children from data in the Nurses’ Health Study II, a long-running investigation on factors that affect women’s health. Other recent studies have reported associations between perinatal exposure to air pollution and ASD in kids. But the EHP study utilized a larger sample of women across the country.

According to the EPA, “Air pollution contains many toxicants known to affect neurological function and to have effects on the fetus in utero.” Women who lived in the most polluted sections of the sample, were up to two times more likely to have a child with ASD than those living in the least polluted areas.  However, the study concludes with the declaration that more research should be done.

“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 risk of autism,” study researcher and associate professor of environmental and occupational epidemiology at Harvard School of Public Health, Marc Weisskopf, told Live Science.

The cause of autism is not specifically known; however, it is “generally accepted that it is caused by abnormalities in brain structure or function.” The results of the study remained consistent after adjusting for other possible ASD risk factors, “such as parents’ income, education, and smoking during pregnancy.” But researchers point out that the findings show a link between exposure to air pollutants and ASD, not “a cause-and-effect relationship.”

Alisha is a writer and researcher for Ring of Fire.