A critical review of developmental exposure to particulate matter, autism spectrum disorder, and attention deficit hyperactivity disorder

Abstract

Autism spectrum disorder (ASD) and attention deficit (hyperactivity) disorder (ADD/ADHD) are key focuses of current health research due to their increasing prevalence. The objective of this systematic literature search and critical review was to evaluate whether the human epidemiologic data indicate a pattern of association between ASD or ADD/ADHD and developmental exposure to particulate matter (PM), with a focus on exposures encountered before the age of three. A MEDLINE and EMBASE search was conducted; following preliminary and full-text screening, 14 relevant articles were identified for review. Three of the 14 studies were prospective cohort studies evaluating exposure to PM; 11 studies had a case-control design. There was no consistent association between developmental PM exposure and ASD across the three of the cohort studies. Seven of the case-control studies examined the relationship between PM and/or PM and ASD; four examined the relationship between developmental diesel PM exposure and ASD. Overall, there was low external consistency in results among studies of PM/PM and ASD, with some reporting high internal consistency without significant associations, others showing associations with high internal consistency for specific exposure windows only (e.g., third trimester), and still others showing high consistency for moderate to strong associations between PM and ASD. The majority of studies reporting significant results had low effect sizes in conjunction with small sample sizes. The four studies of diesel PM and ASD also had low external consistency of results. Only one study evaluated associations with ADD/ADHD, and it found no significant associations with PM. The inconsistent findings across studies of developmental exposure to PM and ASD may be attributed to differences in the study populations, exposure assessments, outcome assessments, or chance. Further research is needed to understand the underlying biological mechanisms that lead to ASD and ADD/ADHD and how PM might be involved in those mechanisms, if at all. High-quality epidemiologic studies are also needed to conclusively determine whether developmental PM exposure is a causal factor for ASD or ADD/ADHD, with focus on a well-developed exposure assessment.

Particulate Matter Exposure and Attention-Deficit/Hyperactivity Disorder in Children: A Systematic Review of Epidemiological Studies

“…This air pollution-related volume decrease may be associated with behavioural problems, such as ADHD and Autism Spectrum Disorder (ASD), as well as to more general behavioural problems [37]. In a recent critical review [11], the authors evaluated whether the data from human epidemiological studies indicate a pattern of association between ASD or ADHD and PM environmental exposure. However, this review included only one study on the association between PM and ADHD, and it found no significant associations with PM 10 .…”

“…Outdoor air pollution and particulate matter (PM), one of its major components, is one of the most serious environmental risks [10]. An etiologic role of air pollution exposure on neurodevelopmental disorders is biologically plausible, although the detailed mechanisms remain elusive [11]. PM is a mixture of solid particles and liquid droplets found in the air that can be inhaled and can cause serious health problems [12].…”

Air Pollution and Noncommunicable Diseases

“…However, many studies have not found associations, and there is a lack of consistency on the pollutant. 47 Air pollution is also harmful to the aging brain. Older adults more heavily exposed to air pollution perform more poorly on cognitive testing and are at increased risk of dementia compared with less exposed adults.…”

The Unexpected Health Effects of Air Pollution

“…Among those potential pollutant-related diseases listed in the Lancet report are a number of neurocognitive diseases, including autism, attention-deficit hyperactivity disorder (ADHD), and adult neurodegenerative disease. A number of investigators have reported that ambient air NO 2 , O 3 , particulate matter (PM) and traffic-related air particulates (TRAPs) are linked to an increased risk of autism [3][4][5]. The periods of exposure to ambient air pollutants associated with autism were during pregnancy and in the 1st year of life.…”

“…The periods of exposure to ambient air pollutants associated with autism were during pregnancy and in the 1st year of life. PM, TRAPs, and NO 2 appear to have the strongest effect on autism development, while ozone was linked to a modest increase in ADHD in a small number of studies, though there remains a need for more definitive studies [3][4][5][6][7]. Overall, PM 2.5 seemed to be the most important pollutant associated with Autism Spectrum Disorder (ASD), and perinatal exposure appears to be the most significant exposure period.…”