Air pollution is another environmental factor that may harm the developing brain. One of the latest studies to explore this connection was published in Environmental Health Perspectives in March.3 Researchers from several universities compared 245 children with ASD and 1,522 controls to investigate the association between autism and gestational exposure to different sizes of particulate matter.

Fine particulate matter (PM2.5), which comes from sources like cars and power plants, is less than 2.5 micrometers in diameter, while coarse particulate matter (PM10-2.5), like dust from a road, has a diameter between 2.5 and 10 micrometers. Particles smaller than 10 micrometers can accumulate in the lungs, and the fine particles may pose the most danger because their size gives them deeper access.4

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According the results, maternal PM2.5 exposure was associated with a 57% increase in a child’s odds of having ASD, while no significant association was found between ASD and PM10-2.5 exposure.

“Potential mechanisms include the influence of particulate matter on the developing brain, in terms of inflammation and effects on the development of the immune system,” study co-author Raanan Raz, PhD, a visiting scientist at Harvard’s T.H. Chan School of Public Health, told Psychiatry Advisor. However, further research is needed to replicate these findings and elucidate exact mechanisms.

Previous research using data from the CHARGE study found increased odds of ASD among children who had been exposed to higher levels of pollution during gestation or the first year of life.5 The odds were often double or more for exposure to PM2.5 and PM10-2.5, as well as to traffic-related air pollution and nitrogen dioxide. “Our results increase our confidence in the hypothesis that autism incidence is influenced, to a large extent, by environmental factors that are modifiable,” said Raz.

They also provide another reason to develop strategies that will reduce air pollution.  The same holds true for reducing exposure to pesticides: it is “largely the responsibility of regulators to remove compounds from the market if they are demonstrating to cause harm to neurodevelopment,” according to Shelton.

Meanwhile, “parents and medical providers should know that agricultural pesticides, some of which are also used in the home, may pose a risk to neurodevelopment,” she added. Pregnant women should avoid direct exposure to pesticides, and they should generally not use insecticide sprays in the home or garden, “as many of these products may elevate maternal blood levels, increasing direct—and potentially harmful—exposure to the fetus.”