Microplastics are detected in bull epididymal sperm and polystyrene microparticles impair sperm fertilization†

An increase in global infertility has coincided with the accumulation of microplastics (MPs) in the environment. This trend is particularly troubling because only 10% of male infertility cases can be attributed to identifiable causes, leaving a knowledge gap in our understanding of their underlying factors. To bridge this, it is important to explore the connection between the accumulation of MPs and the observed decline in male fertility. We assessed the presence of microplastics in epididymal sperm from bulls and used it as baseline concentrations for sperm exposure. MPs were detected in all epidydimal sperm (ES) samples, with a mean concentration of 0.37 μg mL-1. Next, to investigate the effects of MPs on fertility, bovine sperm was exposed to three different concentrations of a mixture of 1.1, 0.5, and 0.3 μm polystyrene (PS) beads: (1) 0.7 μg mL-1, blood concentration of PS in cows (bPS); (2) 0.37 μg mL-1, based on the concentration of total MPs found in ES (esMP); and (3) 0.026 μg mL-1, based on the concentration of PS found in ES (esPS). All sperm samples incubated with PS exhibited reduced motility compared with the control at 0.5 h. However, PS exposure did not affect acrosome integrity or induced oxidative stress. Embryos produced from sperm exposed to PS had reduced blastocyst rates, in addition to increased ROS formation and apoptosis. By employing physiological exposure, this research provided evidence of MPs in bovine epididymal sperm and demonstrated the detrimental effect of PS on sperm functionality.