Polystyrene microplastics enhance the microcystin-LR-induced gonadal damage and reproductive endocrine disruption in zebrafish

The coexistence of eutrophication and plastic pollution in the aquatic environment is becoming a realistic water pollution problem worldwide. To investigate the microcystin-LR (MC-LR) bioavailability and the underlying reproductive interferences in the presence of polystyrene microplastic (PSMPs), zebrafish (Danio rerio) were exposed to individual MC-LR (0, 1, 5, and 25 μg/L) and combined MC-LR + PSMPs (100 μg/L) for 60 d. Our results showed that the existence of PSMPs increased the accumulation of MC-LR in zebrafish gonads compared to the MC-LR-only group. In the MC-LR-only exposure group, seminiferous epithelium deterioration and widened intercellular spaces were observed in the testis, and basal membrane disintegration and zona pellucida invagination were noticed in the ovary. Moreover, the existence of PSMPs exacerbated these injuries. The results of sex hormone levels showed that PSMPs enhanced MC-LR-induced reproductive toxicity, which is tightly related to the abnormal increase of 17β-estradiol (E2) and testosterone (T) levels. The changes of gnrh2, gnrh3, cyp19a1b, cyp11a, and lhr mRNA levels in the HPG axis further proved that MC-LR combined with PSMPs aggravated reproductive dysfunction. Our results revealed that PSMPs could increase the MC-LR bioaccumulation by serving as a carrier and exaggerate the MC-LR-induced gonadal damage and reproductive endocrine disruption in zebrafish.