A recent study has uncovered fresh evidence linking exposure to air pollution with an increased risk of developing autism.

The study of children in Shanghai found that exposure to fine particulate pollution, or PM2.5, correlated with a 78% increase in diagnoses of autism spectrum disorder (ASD). The evidence from the recent study, which monitored the children across a nine-year period, backs up findings from previous research.

A 2014 study of 116,430 pregnant women in the US concluded that increased exposure to PM2.5 during the third trimester doubled the risk of children developing ASD.

Both studies add to a mounting body of evidence linking breathing fine particulate pollution to a wide range of health problems including heart disease, stroke, lung cancer and acute respiratory infections.

The World Health Organization estimates that 7 million premature deaths each year are linked to air pollution.

PM2.5, which have a diameter of less than 2.5 micrometers and are commonly found in industrial flue gases, vehicle exhaust and coal fire fumes, are present at unsafe levels in cities across the world.

Image: Statista

Growing prevalence of autism

The US is one of many countries experiencing a sharp increase in ASD diagnoses, from one in 150 children in 2000 to one in 68 in 2010. While some have put the rise down to greater autism awareness, the link to airborne pollution might offer another explanation.

Although the causes of autism are not yet fully understood and remain the subject of research, the role of genetics has long been recognized.

Research into airborne particulates as an autism risk factor continues to gain traction, thanks to the Shanghai findings and other studies.

The tiny size of airborne particulates means they are easily able to reach deep into the lungs. They contain many of the harmful pollutants commonly found in car exhaust, such as nitrogen oxide, carbon monoxide, sulphur dioxide and heavy metals. These toxins can enter the bloodstream through the lungs and travel to organ tissues around the body.

Children appear to be particularly at risk of illnesses associated with particulate pollution. And the behavioral symptoms of ASD often appear early in development

China’s fight against smog

China is battling an air pollution crisis and has introduced strict measures in recent years to tackle its smog problem.

While the country’s push towards renewables and tighter environmental regulations is helping, there is evidence to suggest that years of exposure to air pollution has already taken a toll on the health of the population.

Of the three particulate categories covered in the Shanghai study – PM1, PM2.5 and PM10 – PM1 are the smallest and most likely to enter the bloodstream through the lungs.

Unfortunately they are also one of the most common and least regulated types of particulate pollution under current international rules.