New Chinese research has found a link between long-term exposure to air pollution from vehicle exhaust, industrial emissions, and other sources to an increased risk of children developing autism.

Carried out by researchers at the University of Chinese Academy of Sciences, along with the University of Birmingham, UK, and McGill University, Canada, the new study is the first to investigate the relationship between long-term exposure to air pollution and autism spectrum disorder (ASD) during early childhood in a developing country.

The researchers looked at 124 children with ASD and 1,240 healthy children who acted as a control group, examining them at different stages over a period of nine years.

The study focused on the health effects of three types of particulate matter -- PM1, PM2.5, PM10, which are all fine airborne particles found in emissions from factories, vehicular exhaust, construction activities and road dust.

The smaller the airborne particles, the better they are able to penetrate the lungs and enter the bloodstream, where they can cause a range of serious health conditions.

PM1 is the smallest in particle size, followed by PM2.5 and PM10. Few studies have been done on PM1 globally and there are no current safety standards for it.

The findings, published in Environment International, showed that exposure to fine particles (PM2.5) from vehicle exhaust, industrial emissions and other sources of outdoor pollution from birth to age three increased the risk of developing ASD by up to 78 percent.

The results are in line with previous studies which have already linked prenatal air pollution exposure to ASD in children.

"The causes of autism are complex and not fully understood, but environmental factors are increasingly recognised in addition to genetic and other factors," said study author Associate Professor Zhiling Guo. "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. 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."

Associate Professor Yuming Guo from Monash University, Australia, commented on the findings, saying, "The serious health effects of air pollution are well-documented, suggesting there is no safe level of exposure. Even exposure to very small amounts of fine particulate matter have been linked to preterm births, delayed learning, and a range of serious health conditions, including heart disease."