Assessment of general toxicity and prooxidant effects of CeO2 and SiO2 nanoparticles on Danio rerio

A diversified use of nanomaterials leads to their accumulation in the environment and involvement into remediation. In water biocoenosis, nanomaterials influence fishes. Lipid peroxidation (LPO) in aquatic bioindicators is considered the parameters generally used to assess an impact of man-caused water pollution. It should be taken into account that the level of LPO products can be due not only to anthropogenic pollution, but also to the presence of peroxide substrates in fish tissues. We firstly showed the effect of silica and cerium nanoparticles in water environment with direct assay of the enzyme activity of the bioindiator used. Our purpose was to evaluate the prooxidant effects of CeO2 (15.8 nm) and SiO2 (40.9 nm) nanoparticles (NPs) on the Danio rerio model, to study LPO as influenced by the NPs doses, and to find out if there are any adaptive mechanisms in Danio rerio to withstand the NPs in the habitat. Complete death of the test objects occurred on days 80 and 84 when CeO2 NPs used. The first signs of the CeO2 NPs toxic effect at a dose of 10 mg/dm3 in the feed appeared on day 45, on day 56 the test-organism number was 33 % lower, and on day 65 a more than 54 % decline occurred. SiO2 NPs led to 33 % reduced survival. The presence of the nanoparticles in the habitat depressed the antioxidant system of Danio rerio but the signs of adaptation were manifested by the end of week 2, and a significant increase in catalase (CAT) and superoxide dismutase (SOD) activity proceeded by the end of the test. At 10 and 100 mg/dm3 of CeO2 NPs the malonic dialdehyde (MDA) level decreased by 11.0 % and 61.0 %, respectively. For SiO2 NPs the changes were similar with the MDA level decrease of 50.0 and 41.5 % at 10 and 100 mg/dm3 dosage, respectively. SOD activity when influenced by CeO2 NPs (10 mg/dm3 and 100 mg/dm3) decreased by 75 and 69 %, respectively, and for SiO2 NPs the indexes were 50 and 26 % lower as compared to control. Similar changes were characteristic of CAT activity. Thus, the investigated nanoparticles possess sufficient toxic properties that necessitates their further study.