Systematic review of the association between particulate matter exposure and autism spectrum disorders.

Particulate matter (PM) as an environmental pollutant is suspected to be associated with autism spectrum disorders. The aim of the present study was to review the epidemiological literature currently available on the relation between PM exposure and diagnosis of ASD. The PubMed database was searched from November 2015 up to January 2016 by one of the authors. We included observational studies (cohort and case-control studies) published in English carried out in children within the last 10 years, measuring PM exposure and health outcomes related to ASD. 13 studies met the inclusion criteria. Four of the studies found no association between PM exposure and ASD. The other 8 studies show positive associations restricted to specific exposure windows which however do not reach statistical significance at times. To conclude, the evidence from the studies allows us to conclude that there is an association between PM exposure and ASD whose strength varies according to the particle size studied with the association with PM and diesel PM being stronger. Given the potential importance for public health, cohort studies with proper adjustment for confounding variables and identification of critical windows of exposure are urgently needed to further improve knowledge about potential causal links between PM exposure and the development of ASD.