Bioaccumulation and sub-acute toxicity of zinc oxide nanoparticles in juvenile carp (Cyprinus carpio): A comparative study with its bulk counterparts

In this study, bioaccumulation and sub-acute toxicity of water-borne nano-ZnO in the test fish, juvenvile carp (Cyprinus Carpio) were evaluated. To clarify the contribution of particle size and free Zn ion to NPs toxicity, its bulk counterparts (bulk-ZnO) and the released Zn2+ were also tested. The results showed that after a 30-day exposure, 50mg/L of nano-ZnO and bulk-ZnO could be significantly accumulated and distributed in various tissues of fish, but nano-ZnO exhibited more hyper-bioaccumulation than bulk-ZnO. Liver and gill might be the target tissues with exposure to nano-ZnO, instead, the target tissue for bulk-ZnO might be intestine. Also, 50mg/L of nano-ZnO caused more severe histopathological changes than the same concentration of bulk-ZnO, which was in accordance with the induction of higher levels of intracellular oxidative stress. The effects of dissolved Zn ions were assessed and the ion toxicity was negligible herein. The results of this study indicated that the observed toxicities of nano-ZnO were not likely a result solely of particle dissolution and identified as a function of particle toxicity and the possibility for a size dependence. The main toxic mechanism of nano-ZnO was possibly by increasing cellular oxidative stress response. ► Nano-ZnO exhibited much higher bioaccumulation and oxidative effects than bulk-ZnO. ► Liver and gill might be target tissues of nano-ZnO, being intestine for bulk-ZnO. ► The effects of dissolved Zn2+ were assessed and the ion toxicity was negligible herein. ► The toxicities of nano-ZnO were identified as a function of particle toxicity and the possibility for a size dependence. ► Appropriate risk assessment should be made concerning nano-ZnO on aquatic ecosystem.