Ecotoxicological effects of differently charged polystyrene nanoparticles on sperm motility and early embryo mortality in European whitefish

Polystyrene, a commonly used plastic, can have significant impacts on natural ecosystems where it accumulates via various ways. While the ecotoxicological effects of nanoparticles on freshwater fish are increasingly understood, charge-dependent toxicity has remained virtually unstudied. Here, we explored the effects of positively and negatively charged polystyrene nanoparticles (250 nm) on sperm quality and early embryo mortality in European whitefish, Coregonus lavaretus. Gametes were exposed to both positively and negatively charged nanoparticles during sperm activation and for three minutes after fertilization (medium concentrations for sperm motility: 0.1, 1 and 10 mg/L, and for embryo mortality, 0.1 and 1 mg/L). The motility parameters (curvilinear velocity, straight line velocity, straightness, linearity) and longevity of activated sperm were analysed by computer-assisted sperm analysis. The early mortality was studied in two family-based settings: 1) a full-factorial mating design of five males × three females, where embryos were incubated in a stable environment, taking into account parental effects in addition to possible PS-NPs induced toxicity, and 2) a single-pair mating design with five full-sib families incubated in a stressful environment (variable turbulence and oxygen conditions). There were no significant differences between the treatments in any of the sperm motility parameters or sperm longevity. In both incubation settings, the highest early embryo mortality was recorded in a group exposed to positively charged nanoparticles. However, the difference was statistically significant only in the stressful environment, where concentration-dependent toxicity of nanoparticles was observed. The present study suggests possible concentration-dependent toxicity effects of PS-NPs on early embryo mortality in whitefish. This study also emphasizes the significance of different incubation conditions, as possible ecotoxicological effects may sometimes be observed only in a stressful environment.