Associations between microplastics and sperm motility parameters in boar semen

Microplastics (MP) are environmental contaminants that pose a potential risk to male reproductive health. The presence of MP in semen may influence sperm functionality by inducing oxidative stress and altering motility or the seminal environment. This study aimed to evaluate the relationship between MP characteristics and boar semen quality. Undiluted semen samples (n = 12) collected from healthy adult boars were analyzed to determine MP particle characteristics using Fourier-transform infrared (FTIR) spectroscopy. Particles were classified by polymer type (nine polymers identified) and size (<50, 50–100, 100–250, 250–500, 500–1000, and ≥1000 µm; particles equal to the lower bound of an interval were included in that interval). Sperm motility parameters were assessed by Computer-Assisted Sperm Analysis (CASA). Associations between MP and CASA parameters were evaluated using Spearman’s rank correlation. Statistically significant correlations were observed between MP concentrations and motility parameters. The percentage of motile spermatozoa in semen was negatively correlated with polyethylene and polyamide particle counts per mL (ρ = –0.608, p = 0.036; ρ = -0.616, p = 0.033, respectively). The total number of MP/mL showed a significant negative correlation with rapid velocity (ρ = –0.608, p = 0.036). Specifically, polyester and polyethylene were negatively correlated with sperm rapid velocity (ρ = -0.803, p = 0.002; ρ = –0.755, p = 0.005, respectively), while MP size fractions (250– 500, 500–1000, and ≥1000 µm) also correlated negatively with this parameter (ρ = –0.769; ρ = –0.727 and ρ = –0.736, respectively, p < 0.01). Conversely, slow velocity parameters were positively correlated with total MP counts, as well as polyester and polyethylene particles. These initial findings indicate that certain types of MP and particle sizes are associated with reduced sperm motility characteristics in boar semen, particularly decreasing rapid velocity while increasing slower motion patterns. This exploratory study highlights a potential link between microplastic contamination and impaired motility of boar sperm, warranting further investigation into the underlying mechanisms and effects of specific polymers.