Polystyrene nanoplastics decrease nutrient accumulation, disturb sex hormones, and inhibit reproductive development in juvenile Macrobrachium nipponense

The biological effects of nanoplastics has grown exponentially over the past few years. However, little is known about the effects of nanoplastic exposure on gonadal development in crustaceans. Thus, juvenile oriental river prawns (Macrobrachium nipponense) were exposed to different concentrations of 75-nm polystyrene nanoplastics (0, 5, 10, 20, and 40 mg/L) for 28 days to study the effects of exposure to nanoplastics on gonadal development. The genes encoding extracellular signal-regulated kinase (ERK) and mitogen-activated protein kinase kinase (MEK) were selected and the nutrient composition, sex hormone level, and gonad development-related gene expression were determined. Crude lipid and crude protein decreased with exposure to higher concentrations of nanoplastics, whereas there were no significant differences in levels of ash or moisture (P > 0.05). Full-length Mn-ERK and Mn-MEK cDNAs were cloned from M. nipponense and homologous comparisons showed that the genes had conserved functional sequences and had evolved consistently in invertebrates. With nanoplastics concentration increased, the serum sex hormone (estradiol, progesterone, and testosterone) levels of juvenile shrimp first increased and then decreased. In addition, the expression of gonad development-related genes (Vitellogenin, Vitellogenin receptor, Cyclin B, Gametocyte Specific Factor 1, Vasa, and PL10), MEK and ERK initially increased and then decreased with increasing nanoplastic concentration. This suggests that polystyrene nanoplastics reduce the accumulation of nutrients and lead to suppression of gonadal development in juvenile M. nipponense and, thus, provides basic information on the toxic effects of nanoplastics that could extend to other crustaceans.