Individual and Joint Effect of Particulate Matter and Night-Time Temperature on Sperm Quality: A Large Retrospective Cohort Study in China

The joint effect of particulate matter (PM) and night-time temperature on sperm quality remains unclear. We aimed to investigate the individual and joint effects of PM and night-time temperature on sperm quality. This population-based cohort study with 19,318 volunteers and 55,610 semen samples was conducted in Henan, China, from 2013 to 2020. High spatial resolution gridded data sets were used to estimated individual PM (PM₁, PM_2.5, and PM₁₀) and night-time temperature exposures during the entire period (0-90 lag days) and three critical periods (0-9, 10-14, 70-90 lag days) of sperm development. Generalized linear mixed models assessed the individual and joint effects on sperm quality. We found that the per interquartile range (IQR) increase in PM₁ throughout spermatogenesis was associated with decreased sperm count (β, -0.068; 95% CI: -0.116, -0.021). Increasing PM_2.5 per IQR was related to reductions in sperm concentration 0.052 (95% CI: -0.098, -0.005) and sperm count 0.086 (95% CI: -0.134, -0.039). Night-time temperature was negatively related to sperm concentration, sperm count, and sperm motility (all <i>P</i> < 0.05). Combined higher night-time temperatures and PM₁ (or PM_2.5) concentrations significantly impacted sperm concentration, count, and motility (all <i>P</i> _interaction < 0.05). Synergistic effects of night-time temperature and PM₁ on abnormal progressive motility were observed (relative excess risk due to interaction (RERI), 0.27; 95% CI: 0.02, 0.53). Similar joint effects of night-time temperatures and PM_2.5 and PM₁₀ on sperm quality were observed. Our results suggested that individual and joint effects of night-time temperature and PM exposure negatively impact sperm quality. These findings highlight the need for public health strategies to mitigate air pollution and global warming and promote male reproductive health.