Assessing the chronic exposure of copper oxide and zinc oxide nanoparticles in zebrafish

In the present time, nanomaterial toxicological studies have become important due to the persistent presence of engineered nanomaterials in the environment. Zebrafish are a versatile and well-established model organism for biosafety assessments of nanomaterials and other toxicants. The present study aimed to investigate the long-term effects of low concentrations of copper oxide (CuO) nanoparticles (NPs) and zinc oxide (ZnO) NPs on zebrafish focusing on their potential toxicological impact. The effects of CuO NPs and ZnO NPs at varying concentrations (0.01, 0.05, and 0.1 µg/mL) were assessed in adult zebrafish over 730 days (2 years). At the end of the exposure period, the effects were observed through the study of mortality and body weights, histopathological analysis of gills and intestines, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of Zpr1, Vtg1, and Th1 genes, levels of tyrosine hydroxylase in zebrafish brain, and study of malformations in F1 generation of the treated zebrafish. CuO NPs caused mortality and malformations of embryos at 0.1 µg/mL concentration whereas no such effect was observed in the case of ZnO NPs. The weights of zebrafish treated with CuO NPs decreased with time. It was explained by the disruption of the villi of these zebrafish after H E staining. CuO NPs were also found to disrupt the morphology of the gills of zebrafish over a while. The fold change in the genes related to the Zpr1, Th1, and Vtg1 genes also suggested the potential toxicity caused by CuO NPs. In immunohistochemistry studies, CuO NPs were found to increase the levels of tyrosine hydroxylase in the zebrafish brain, pointing out its interference with the swimming patterns of the zebrafish and the induction of stress. The F1 generation of CuO NPs-treated fish showed a decrease in reproducing ability along with the malformations in the F1 generation. Therefore, CuO NPs caused chronic toxicity at low concentrations whereas no such toxicity was observed in the case of ZnO NPs. The data from our study indicated that CuO NPs exhibited elevated toxicity even at lower concentrations when exposed over an extended period. In contrast, exposure to ZnO NPs did not show any significant toxicity effects on zebrafish.