Air pollution during pregnancy linked to autism risk

A major new study examining more than 2 million births in Ontario, Canada, has found that exposure to certain air pollutants during pregnancy is associated with an increased risk of autism in children.

Researchers analysed data from 2,183,324 births between 2002 and 2022, tracking children until age five to identify autism diagnoses. The study focused on  PM2.5, examining which specific components might be driving the connection to autism.

The findings revealed that two particular components showed the strongest associations: sulfate and ammonium. Pregnant women exposed to higher levels of these pollutants had children with elevated autism risk, with increases of 15% and 12% respectively for each standard unit increase in exposure.

Importantly, the research identified specific windows of vulnerability during pregnancy. The second and third trimesters – roughly weeks 14 through 36 – appeared to be the periods when exposure carried the highest risk. This timing coincides with crucial stages of foetal brain development, including the formation of neural connections and the organisation of brain tissue.

The study also found that exposure to ground-level ozone during a baby’s first year of life was also linked to autism risk, suggesting that environmental threats extend beyond the womb into early infancy, when the brain continues to develop rapidly.

Sulfate pollution primarily comes from coal-fired power plants, oil refineries and ships burning high-sulphur fuel. Ammonium stems from agricultural fertilisers and sewage treatment. These pollutants may trigger neuroinflammation and oxidative stress, potentially disrupting normal brain development.

The research revealed patterns of environmental inequality. The pollution-autism link was strongest in urban areas, particularly in low- and middle-income neighbourhoods with higher proportions of racial minorities, communities that tend to be located closer to highways and industrial facilities.

The researchers noted: ‘These findings highlight the need for public health strategies to reduce air pollution, particularly in urban and socioeconomically disadvantaged communities.’ 

The study’s large scale and detailed exposure data make it one of the most comprehensive investigations to date of how specific air pollutants and timing of exposure relate to autism risk. 

The full research can be read here.

Photo: Natalia Marcelewicz/Unsplash