PM_2.5 exposure causes decreases in total sperm count and concentration: dual evidence from a cohort study and systematic evaluation with TRAEC strategy

Current evidence on whether exposure to fine particulate matter (PM_2.5) affects male semen quality exhibits considerable heterogeneity, and a systematic evaluation of PM_2.5 spermatotoxicity is lacking. This study aims to provide new evidence on the association between PM_2.5 exposure during the spermatogenic cycle and semen parameters in a representative population of reproductive age men, and to conduct a systematic evaluation integrating existing evidence from population, animal, and cellular studies.

Based on the Chongqing Preconception Reproductive Health and Birth Outcome Cohort, a questionnaire survey was conducted on male volunteers with pregnancy plans recruited in Chongqing Maternal and Child Health Hospital from November 2018 to September 2023. Their semen samples were collected and analyzed following standardized procedures, including semen volume, total sperm count, sperm concentration, progressive motility, total motility, and normal sperm morphology. PM_2.5 exposure data were obtained from the Tracking Air Pollution in China (TAP) dataset. Individual-level exposure during different stages of the spermatogenic cycle was estimated based on the residential addresses from the recovered questionnaires. Multiple linear regression analysis was employed to estimate the dose-response relationships between PM_2.5 exposure and semen parameters. Targeted Risk Assessment of Environmental Chemicals (TRAEC) strategy was adopted for systematic evaluation. Eligible studies were retrieved from PubMed, Web of Science, and ScienceDirect databases. The findings from the cohort analysis were also incorporated to jointly assess the reproductive toxicity of PM_2.5 exposure, yielding a comprehensive quantitative score, and determine the risk level according to predefined criteria.

The cohort study enrolled 5735 male volunteers subjected from January 2018 to September 2023, with a mean age of 31.42±4.58 years. Each interquartile range increase in PM_2.5 exposure during the spermatogenic cycle was associated with a 12.30% (95%CI: -16.21 to -8.22, P<0.0001) decrease in total sperm count and a 10.25% (95%CI: -13.64 to -6.72, P<0.0001) decrease in sperm concentration. The TRAEC-based evaluation incorporated 41 studies, revealing that PM_2.5 exposure during the spermatogenic cycle posed a moderate risk for total sperm count and total motility, and a low risk for sperm concentration, progressive motility, semen volume, and normal sperm morphology.

Both the cohort study and the TRAEC-based systematic evaluation consistently demonstrate that PM_2.5 exposure primarily causes decreases in total sperm count and sperm concentration, suggesting potential spermatogenic toxicity of PM_2.5 exposure.

It is recommended that health authorities should leverage the existing maternal and child healthcare networks and preconception screening systems to simultaneously issue reproductive health protection alerts during air pollution episodes, and to provide targeted health education and risk communication for men planning pregnancy.