With the memory of the discredited autism-vaccine scare fresh in our minds, it can be easy to forget that there is still a great mystery surrounding the cause(s) of autism spectrum disorder (ASD). The incidence of diagnosed ASD has steadily increased throughout the decades, and while much of this rise can be tied to statistical magic and a greater awareness of its symptoms, many experts believe there are outside factors influencing its emergence, now believed to afflict one of every 68 children in America. One such proposed candidate has been air pollution. Now, a recent study from the University of Pittsburgh has lent more support to that theory, finding that exposure to fine particulate air pollution during pregnancy as well as throughout the first two years of the child's life may be associated with an increased risk of autism.

The study authors interviewed the families of over 200 children diagnosed with ASD alongside a similarly sized control sample in Southwestern Pennsylvania. They then approximated the mother’s and child’s exposure to levels of air pollution before, during and after pregnancy, specifically to particles of pollutant smaller than 2.5 millimeters in diameter, such as dirt or soot (PM2.5). After controlling for other possible risk factors like the mother’s age and smoking history, the authors found that there was a significant correlation between cumulative pollution exposure to later development of ASD. High exposure predicted a 50 percent increase in the rate of autism compared to low exposure. "Our data indicate that both prenatal and postnatal exposures to PM2.5 are associated with increased risk of ASD," the authors concluded.

As they further explain, their conclusions have been echoed by similar studies finding a pollution link to autism. But there are still a lot of unanswered questions about how exactly pollution exposure influences the rate of autism, believed to be caused by both environmental and genetic factors. And their results do not prove a direct cause-and-effect relationship between pollution and autism. "Our findings reflect an association, but do not prove causality,” said lead author Dr. Evelyn Talbott, professor of epidemiology at the University of Pittsburgh, in a press release. "Further investigation is needed to determine possible biological mechanisms for such an association."

Regardless, while pollution levels have somewhat abated over the years, there is a laundry list of known health dangers from overexposure, including asthma, cancer and decreased life expectancy. These risks and others have prompted advocates to push for more stringent environmental regulations. It seems that this study will only add more clean-burning fuel to that fire.

Source: Talbott E, Arena V, Rager J, et al. Fine particulate matter and the risk of autism spectrum disorder. Environmental Research. 2015