Association between exposure to ambient air pollution and semen quality: A systematic review and meta-analysis

Background: Accumulating evidence has linked exposure to ambient air pollution to a reduction in semen quality; how-ever, the exposure-response associations are yet to be synthesized.Objective: To summarize the exposure-response associations between air pollution and semen quality.Methods: We systematically searched PubMed, Embase, and Web of Science for relevant studies published before April 20, 2022. Studies investigating the exposure-response association of PM2.5, PM10, SO2, NO2, CO, and O3 with semen quality written in English were included. Semen quality parameters included semen volume, sperm concentration, total sperm number, total motility, progressive motility, and normal forms. Random-effects and fixed-effects models were performed to synthesize associations in the meta-analysis. Results: The search returned 850 studies, 11 of which were eligible for meta-analysis. Each 10 mu g/m3 increase of expo-sure to PM10 and SO2 was respectively associated with a 2.18 % (95 % confidence interval [CI]: 0.10 %-4.21 %) and 8.61 % (1.00 %-15.63 %) reduction in sperm concentration, and a 2.76 % (0.10 %-5.35 %) and 9.52 % (5.82 %-13.93 %) reduction in total sperm number. Each 10 mu g/m3 increase of exposure to PM2.5 and PM10 was respectively associ-ated with a 1.06 % (95 % CI: 0.31 %-1.82 %) and 0.75 % (0.43 %-1.08 %) reduction in total motility, and a 0.55 % (0.09 %-1.01 %) and 0.31 % (0.06 %-0.56 %) reduction in progressive motility. No association was observed for PM2.5 or PM10 with semen volume;PM2.5, NO2, CO, or O3 with sperm concentration or total sperm number; and gaseous air pollutants with total or progressive motility. The association between air pollution and normal forms was not summa-rized due to insufficient number of studies. No significant publication bias was detected.Conclusions: Exposure to ambient PM2.5, PM10, and SO2 was inversely associated with sperm concentration, total sperm number, total motility, and/or progressive motility. Our findings add to the evidence that air pollution may lead to ad-verse effects on male reproductive system and suggest that reducing exposure to air pollution may help maintain better semen quality.