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Abstract: The acute toxicity and oxidative effects of nano-scale titanium dioxide, zinc oxide and their bulk counterparts in zebrafish were studied. It was found that although the size distribution of nanoparticles (NPs) was similar to that of the bulk particles in suspension, the acute toxicity of the TiO2 NPs (96-h LC50 of 124.5mg/L) to zebrafish was greater than that of the bulk TiO2, which was essentially non-toxic. The acute toxicities observed for ZnO NPs, a bulk ZnO suspension, and a Zn2+ solution were quite similar to each other (96-h LC50 of 4.92, 3.31 and 8.06mg/L, respectively). In order to explore the underlying toxicity mechanisms of NPs, ·OH radicals generated by NPs in suspensions and five biomarkers of oxidative effects, i.e. superoxide dismutase, catalase activities, malondialdehyde, reduced glutathione and protein carbonyl were investigated. Results showed that after the illumination for 96h, the quantities of ·OH in the NP suspensions were much higher than ones in the bulk particles suspensions. The malondialdehyde content of zebrafish gills exposed to either illumination or dark were 217.2% and 174.3% of controls, respectively. This discrepancy indicates the occurrence of lipid peroxidation which is partly due to the generation of ·OH. In contrast, exposure to 5mg/L ZnO NPs and bulk ZnO suspension induced oxidative stress in the gills without oxidative damage. Oxidative effects were more severe in the livers, where the protein carbonyl content, in the light and dark groups exposed to 50mg/L TiO2 NPs, was 178.1% and 139.7% of controls, respectively. The malondialdehyde levels in the liver of fish exposed to 5mg/L ZnO NPs and bulk ZnO were elevated (204.2% and 286.9% of controls, respectively). Additionally, gut tissues exhibited oxidative effects after exposure to NP suspensions. These results highlight the importance of a systematic assessment of metal oxide NP toxicity mechanisms. [Copyright &y& Elsevier]

Heavy metal pollution has posed a potential hazard to the ecological environment and human health. Herein, a novel ternary magnetic adsorbent (Fe 3 O 4 /g-C 3 N 4 /Carbon layer, Carbon layer: hydrothermal products from sucrose) was synthesized through a simple hydrothermal carbonization (HTC) method for removal of hexavalent chromium (Cr (VI)) removal. The Carbon layer (CL) formed during the HTC of carbon precursors (sucrose) acted as a reducing agent. Also, it has abundant oxygen-containing groups on its surface. The Fe 3 O 4 /g-C 3 N 4 /CL had a high removal capacity for Cr (VI) (50.09 mg/g), and excellent regeneration and magnetic separation performance. Importantly, the Fe 3 O 4 /g-C 3 N 4 /CL could not only improve the adsorption ability for Cr (VI), but also strengthen the immobilization of Cr (III). Based on the comprehensive experiments and characterization, combined with DFT calculations, we proposed that, the first time, the removal of Cr (VI) was controlled by three consecutive processes: (1) ion exchange of Cr (VI) by hydroxyl groups, (2) reduction of Cr (VI) to Cr (III) by electron-donor (oxygen-containing) groups (EDGs), and (3) complexation of Cr (III) by amine groups. This study provides a new avenue for the removal of toxic oxygen anions and reveals an original removal mechanism of Fe 3 O 4 /g-C 3 N 4 /CLx (x = hydrothermal products from carbon precursors (glucose, ascorbic acid, cellulose))., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2020 Elsevier B.V. All rights reserved.)