Association of sulfur dioxide exposure with sperm quality in reproductive-aged men: the mediating and moderating roles of essential elements in seminal plasma

Currently, there are limited data to support the association between sulfur dioxide (SO2) exposure and semen quality. Here, we analyzed nine elements including vanadium (V), chromium (Cr), iron (Fe), copper (Cu), cobalt (Co), nickel (Ni), manganese (Mn), selenium (Se), and strontium (Sr) in seminal plasma of 738 participants using inductively coupled plasma mass spectrometry (ICP-MS). Each participant was assigned an average SO2 exposure of 0-90 days preceding semen collection. Associations were determined using multivariable linear models, susceptible exposure windows were identified via distributed lag nonlinear models (DLNM), and indirect effects and effect modification were examined based on mediation and interaction analyses. Notably, SO2 exposure was negatively associated with sperm concentration (β: -0.07; 95% confidence interval [CI]: -0.13 to -0.01; P = 0.02), total sperm count (β: -0.09; 95% CI: -0.15 to -0.03; P < 0.01), progressive motility (β: -0.04; 95% CI: -0.07 to -0.01; P = 0.02), and total motility (β: -0.03; 95% CI: -0.07 to -0.01; P < 0.01), but positively associated with sperm abnormal morphology (β: 0.27; 95% CI: 0.12 to 0.42; P < 0.01). DLNM identified a susceptibility window during spermiogenesis (lags 37-69 days). Se was positively associated with sperm concentration (β: 0.34; 95% CI: 0.23 to 0.45; P < 0.01) and total sperm count (β: 0.28, 95% CI: 0.16 to 0.40; P < 0.01), mediating 23.6% and 14.6% of the effects of SO2, respectively. A significant interaction between SO2 and Ni was detected in sperm abnormal morphology (β: 0.28; 95% CI: 0.05 to 0.51; P = 0.02). These results indicate that SO2 exposure may reduce semen quality, and this effect may be mediated by Se and modified by Ni.