Exposure to air pollution could cause autism and autism-like traits, according to a review examining the long-term effects of pollution exposure on autism spectrum disorder (ASD) during a child’s early life. 

Causes of autism are not fully understood and, while genetic factors are believed to account for more than half of those contributing to autism, environmental and other factors are increasingly being recognized as potential causes.

"The developing brains of young children are more vulnerable to toxic exposures in the environment and several studies have suggested this could impact brain function and the immune system," said Yuming Guo, from Monash University's School of Public Health and Preventative Medicine, in a statement. "These effects could explain the strong link we found between exposure to air pollutants and ASD, but further research is needed to explore the associations between air pollution and mental health more broadly." 

Publishing their work in Environment International, researchers reviewed multiple studies in humans and animals examining the long-term effects of pollution exposure on ASD in the womb and during a child’s early life looking specifically at the health effects of three types of particulate matter (the fine airborne particles that are byproducts of emissions from factories, construction, and vehicle pollution, among other things). The study incorporated a total of 124 children with ASD and 1,240 healthy children as controls. The team found that exposure to certain types of pollution can increase the risk of developing ASD by up to 78 percent. 

One such byproduct called dioxin causes changes – such as malfunctions of the mitochondria, thyroid gland, and nerve cell communication – that can result in autism. Dioxins are a byproduct of certain industrial processes like bleaching paper or making various pesticides and herbicides. Since they poorly degrade, dioxins accumulate in the environment and atmosphere and turn up in living organisms. People are most commonly exposed to them through animal-based foods like dairy or meat. And when a child is exposed to dioxins during their most vulnerable brain development phases, they appear to experience an increased risk of developing ASD or ASD-like traits.

However, the authors note that the presence of other pollutants likely affects the development of ASD, so it is difficult to say whether dioxins directly lead to the condition.  

Autism is a growing public health concern as more and more cases are detected each year, though partially because of our ability to more accurately diagnose the condition. In the last 50 years, more than 80,000 new synthetic chemicals have been developed, 3,000 of which are widely used and pose a risk to humans. Understanding how these chemicals impact human health could inform global standard policies meant to reduce harm in the future.