Exotoxicology Assessment on the Adverse Effects of Zinc Oxide Nanoparticles in a Model Native fish, Cnesterodon decemmaculatus

Abstract

The use and production of nanoparticles (NPs) in recent years has grown exponentially due to their multiple physical and chemical properties. In particular, zinc oxide (ZnO) NPs have several applications for medicinal use, among which we can mention: anticancer treatment (photodynamic, photothermal, and sonodynamic therapy), theragnostic (bioimaging), drug delivery, tissue engineering, radiation filter (insunscreens, cosmetics), antimicrobial agents (toothpaste, dentistry implants, food packaging, food additive). Due to diverse applications and daily use, they are widely distributed and can easily reach bodies of water. Also, it has been detected in aquatic environments generating invertebrate and vertebrate mortality from 3.2 mg/L ZnO. Added to this, sub-lethal effects have been reported on zebrafish model: immunotoxicity, developmental alterations, abnormalities neurotoxicity, reproductive, cardiovascular, hepatotoxicity and genotoxicity. However, in our regions, studies on the toxicity of ZnO NPs are scarce. For example, there are no evaluations on the adverse effects of ZnO NPs on native fish. It is important to note that studies using native species allow a better understanding of ecosystem functioning, so their use has great advantages for carrying out ecotoxicological bioassays. Environmental monitoring showed ZnO NPs in surface waters worldwide being detected in concentrations between 0.001 to 0.1 mg/L. In this context, the objective of this work was to evaluate the response to different relevant sublethal concentrations of ZnO NPs in a local fish Cnesterodon decemmaculatus. Acute toxicity bioassays were carried out using sublethal concentrations between 1 and 10 mg/L of ZnO NPs based on LC50 values from the literature. Biochemical biomarkers were studied: catalase (CAT), cholinesterase (ChE) and inhibition of lipid oxidation (TBARS) after 96h of exposure to the xenobiotic. The results suggest that the evaluated concentrations do not produce mortality in C. decemmaculatus. The biomarkers showed significant differences in ChE for fish exposed to 1 mg/L, while in CAT no significant differences were observed in the antioxidant response after acute exposure. Finally, TBARS activity decreased significantly compared to the control group at the highest concentrations (5 and 10 mg/L). This study shows that the presence of ZnO NPs in water bodies can represent a risk for the fauna that inhabit them and for human health.