Particles rather than released Zn2+ from ZnO nanoparticles aggravate microplastics toxicity in early stages of exposed zebrafish and their unexposed offspring

Knowledge on the interaction between microplastics (MPs) and zinc oxide nanoparticles (ZnO NPs) is limited. Here, we investigated effects of embryo-larvae exposure to 500 μg/L polystyrene MPs (5 µm), 1200 μg/L ZnO NPs (< 100 nm), 500 μg/L dissolved Zn2+ from ZnSO4, and the mixtures of MPs and ZnO NPs or ZnSO4 on exposed F0 larvae and unexposed F1 larvae. Consequently, ZnO particles adhered to MPs surfaces rather than Zn2+, and increased Zn transport into larvae. Growth inhibition, oxidative stress, apoptosis, and disturbance of growth hormone and insulin-like growth factor (GH/IGF) axis were induced by MPs and ZnO NPs alone, which were further aggravated by their co-exposure in F0 larvae. MPs + ZnO increased apoptotic cells in the gill and esophagus compared with MPs and ZnO NPs alone. Reduced growth and antioxidant capacity and down-regulated GH/IGF axis were merely observed in F1 larvae from F0 parents exposed to MPs + ZnO. Contrary to ZnO NPs, dissolved Zn2+ reversed MPs toxicity, suggesting the protective role of Zn2+ may be not enough to ameliorate thfie negative effects of ZnO particles. To summarize, we found that particles rather than released Zn2+ from ZnO nanoparticles amplified MPs toxicity in early stages of exposed zebrafish and their unexposed offspring.