Persistent organic pollutants exposure and risk of autism spectrum disorders: A systematic review and meta-analysis

Accumulating number of epidemiological studies has recently proposed that improvement in the risk of autism spectrum disorders (ASD) is associated with persistent organic pollutants (POPs) exposure. However, evidence from current researches is limited and inconsistent. Thus, we conducted a systematic review and meta-analysis to investigate the potential associations comprehensively. We systematically and extensively searched two electronic databases (PubMed and EMBASE) from inception to July 3, 2022 and an updated search was performed before submission. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were derived from stratified random-effects meta-analyses by type of exposure and outcome. We also tested the potential heterogeneity across studies, conducted sensitivity analysis and evaluated publication bias. A total of 20 studies were finally included in our study. Meta-analytical effect estimates indicated a positive association between prenatal exposure to PCB-138, PCB-153 and PCB-170 and an increased risk of ASD, with OR of 1.89 (95% CI = 1.21-2.95, I² = 0%), 1.61 (95% CI = 1.05-2.47, I² = 0%) and 1.46 (95% CI = 1.03-2.06, I² = 0%) respectively. In contrast, PFDA was found inversely associated with the risk of ASD (OR = 0.70, 95% CI = 0.52-0.94, I² = 0%). The level of evidence supporting a link between ASD risk and exposure to PCB-138, PCB-153, PCB-170, and PFDA was respectively categorized as low, low, moderate, and low. In summary, this systematic review and meta-analysis suggest that exposure to PCB-138, PCB-153, and PCB-170 correlates with a heightened risk of ASD, with evidence levels rated as "low", "low", and "moderate", respectively. In contrast, PFDA exposure appears to be inversely associated with ASD risk, with a "low" level of supporting evidence. However, due to the limited number of studies available for each exposure and outcome pairing, these results should be interpreted with caution. Sufficiently powered studies are needed to validate our findings.