Toxicological effects of manufactured nanoparticles (TiO2, CuO & ZnO) on tilapia (Oreochramis mossambicus)

Abstract

Advancement in nanotechnology and its growing use in multiple commodities are raising concerns about nanotoxicity. Some mammalian in vitro studies have reported the potential toxic effects of TiO2-NPs. However, the existing data on toxicity of these materials in aquatic environment is not adequate. In present study the effects of manufactured nanoparticles like TiO2, CuO and ZnO were investigated on tilapia (Oreochromis mossambicus). Bioaccumulation, oxidative and anti-oxidant defense mechanism alongwith histological alterations and genotoxicity was also assessed. For the experiment, the stock solution of TiO2-NPs were prepared by sonication. Fish were acclimatized for seven days in semi-static system before the start of experiment. In this study the sub-lethal effects of various doses such as 0 mg/L (T0, Control), 0.5 mg/L (T1), 1.0 mg/L (T2) and 1.5 mg TiO2-NPs/L (T3) on tilapia housed in semi static water tanks for fourteen days. The accumulation was increased with the increasing concentration of TiO2-NPs and higher values were observed in the liver as compared to the gill and muscles. The significant difference was found among the control and the metal-exposed fish (p<0.05). The lipid peroxidase (LPO), catalase (CAT) and glutathione (GSH) levels were significantly higher in gill than the liver samples (p<0.05). Conversely, the superoxide dismutase (SOD) level was increased with the increased TiO2-NPs concentration in liver as compared to the gills (p<0.05). Histological alterations were also observed in the gills and liver of the fish. In gills hyperplasia, fusion of gill lamellae, rupturing of gills filaments and thickening of primary and secondary gill lamellae were present. In liver necrosis and apoptosis with condensed nuclear bodies and sinusoid spaces in relation to parenchyma increased with the increase in TiO2-NPs concentration. Genotoxic potential was elaborated by evaluating DNA strand breaks using alkaline comet assay. 2 Exposure to TiO2-NPs was responsible for DNA damage in the erythrocytes. The higher value of % tail DNA and olive tail movement was observed with increasing concentration of TiO2-NPs. The significantly higher values of % tail DNA and olive tail movement (product of tail length and amount of DNA in comet tail) were observed to have the same pattern for all the treatments when compared with the control. This study concluded that the titanium dioxide nanoparticles have more potential to accumulate in the soft tissues, showing respiratory distress such as oxidative stress and induction of anti-oxidant defense by raising glutathione (GSH), organ pathology and genotoxicity. Metal oxide nanoparticles are widely used in industries and peak level can be confirmed in their surroundings. In the present study the sub-lethal effects of CuONPs from low to high concentration; as control (0 mg/L), T1 (0.5 mg/L), T2 (1.0 mg/L) and T3 (1.5 mg/L) were observed on Oreochromis mossambicus. Accumulation of Cu from CuO-NPs was increased with the increase in doses and maximum value was found in gills as compared to liver and muscles. The increased LPO level was observed in gill as compared to liver and the similar results were obtained in CAT and GSH while SOD level was higher in liver than gills. In histological alterations, gill oedema, curved tips, fusion of gill lamellae and thickening of primary and secondary gill lamellae was observed. Necrosis and apoptosis with condensed nuclear bodies, pyknotic nuclei and oedema were observed in liver at highest dose of CuO-NPs. In genotoxic study, the highest value of % tail DNA and olive tail movement was observed with increasing concentrations. Copper oxide nanoparticles has greater potential to accumulate in the soft tissues, which may causes respiratory distress such as oxidative stress, induction of anti-oxidant defense by raising glutathione, organ pathology and genotoxicity. 3 ZnO-NPs are being largely utilized in a number of manufacturing companies and commercial applications. No sufficient data is available to assess the toxic potential of ZnO-NPs to aquatic organisms. This study was designed to investigate the possible mechanisms of bioaccumulation, oxidative stress, histopathological alterations and genotoxicity induced by ZnO-NPs to tilapia (Oreochromis mossambicus). Bioaccumulation of Zn from ZnO-NPs in various tissues (gills, liver and muscles) was investigated and higher Zn accumulated in liver as 3.0643 mg/Kg (ANOVA p<0.05) at highest concentration T3 (1.5 mg/L). ZnO-NPs may also induce oxidative stress by altering the activity of oxidative and anti-oxidant enzymes activity. In this study significantly increased LPO level was observed in gill as compared to liver (ANOVA p<0.05). The similar results with increase in CAT and GSH level were also observed. Whereas, the SOD level was significantly rises at higher dose of ZnO-NPs again in gills as compared to the liver (ANOVA p<0.05). In case of Histological alterations; gills hyperplasia, fusion of gill lamellae and thickening of primary and secondary gills lamellae was observed. In liver, necrosis and apoptosis with condensed nuclear bodies, and pyknotic nuclei was observed in relation to parenchyma. The genotoxic potential was elaborated by evaluating DNA strands break using alkaline comet assay. Exposure of tilapia to ZnO-NPs was responsible for DNA damage in the erythrocytes. Maximum % tail DNA and olive tail movement was documented when blood was exposed to ZnO-NPs. Significant difference was found in % tail DNA and olive tail movement (OTM) at various doses and increased with the rise in dose concentration for all treatments compared to the control (ANOVA p<0.05). Overall we concluded that the zinc oxide nanoparticles (ZnONPs) has more potential to accumulate in the soft tissues, causes respiratory distress such as oxidative stress, induction of anti-oxidant defenses by raising glutathione 4 (GSH), organ pathology and genotoxicity. These results concluded the potential ecotoxicological effects of nanoparticles in understanding their uptake and effects in aquatic environment particularly for aquatic biota.