Exposure to individual organophosphate esters and their mixture in relation to semen quality in Chinese men

BACKGROUND: Organophosphate esters (OPEs), widely used as flame retardants and plasticizers in consumer products, are toxicologically linked to potential adverse effects on male reproductive health. However, epidemiological evidence remains limited and inconsistent. OBJECTIVES: This study aimed to investigate the associations between exposure to individual OPEs and their mixture with semen quality among men in China. METHODS: We enrolled 796 sperm donors from the Shanghai Human Sperm Bank. Semen quality was assessed based on normal morphology, sperm concentration, progressive motility, semen volume, and semen concentration. Urinary concentrations of fourteen OPEs metabolites (including 8 organophosphate flame retardants [OPFRs] and 6 organophosphate pesticides [OPPs]) were quantified using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS-MS). Multiple linear regression assessed associations between individual OPEs and semen quality parameters. The joint effects of the OPE mixture were evaluated using quartile-based g-computation (QGC) and Bayesian kernel machine regression (BKMR). RESULTS: Low semen quality was observed in 26.5 % of donors. Compared to the first tertile, subjects in the third tertile of urinary O,O-dimethyl thiophosphate (DMTP) and O,O-diethyl phosphate (DEP) exhibited decreases in progressive motility of 3.81 % (95 % confidence interval [CI]: -6.61 %, -1.01 %) and 3.06 % (95 % CI: -5.80 %, -0.32 %), respectively. QGC analysis revealed a significant negative association between the OPE mixture and progressive motility (β = -2.24; 95 % CI: -4.16, -0.31). BKMR analysis confirmed this inverse relationship and identified DMTP as the primary contributor. CONCLUSIONS: Environmental exposure to OPEs, particularly OPP metabolites such as DMTP, was associated with reduced sperm progressive motility in healthy men.