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 Zn(2+) 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.
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