Adverse associations of ambient fine particulate matter & components with semen quality and the mitigating role of residential greenness: Evidence from the PREBIC study in China.

Exposure to fine particulate matter (PM2.5) has been associated with impaired semen quality, but the potential mitigating role of residential greenness remains unclear. We conducted a hospital-based prospective cohort study of 3770 Chinese men who underwent 4847 semen examinationin in Chongqing, China (2018-2023). Exposure to PM2.5 and its components (SO42-, NO3-, NH4+, OM, BC) was estimated for the 0-90 days preceding semen collection, while residential greenness was assessed using satellite-derived normalized difference vegetation index (NDVI) over the same period. Semen quality parameters including progressive motility, non-progressive motility, total motility, sperm concentration, total sperm count, and viability, were assessed according to WHO 5th edition guidelines. Linear mixed-effects models were used to examine associations between environmental exposures and semen quality and their interactions. Higher exposure to PM2.5 and its components was associated with poorer semen quality, including reduced progressive motility, sperm concentration, sperm count, sperm viability, and total motility. For instance, per IQR increase in PM2.5 was associated with a 2.0% decrease in progressive motility (-3.7%, -0.3%) and a reduction in total sperm count of 0.108 million sperm (-0.160, -0.056). In contrast, higher residential greenness was positively associated with total sperm count. Significant interactions were observed between greenness and PM2.5 or SO42- for progressive and total sperm motility, with higher greenness mitigating adverse effects, particularly at lower SO42- levels. The observed associations varied across age, BMI, education levels, adverse lifestyle factors, and season. These findings highlight the potential role of urban green spaces in protecting male reproductive health.