Exploring the Interactive Toxicological Impacts of Sodium Arsenite and Copper Oxide Nanoparticles on Zebrafish Danio rerio (H.)

Abstract

Background: Sodium arsenite is widely known for its use as herbicide in agriculture and has been found to be highly toxic to exposed organisms. Nanoparticles are emerging pollutants that can affect the toxicological risks associated with the already existing contaminants after interacting with them. Nanoparticles due to their variety of unique properties can impact the toxicity of sodium arsenite when jointly exposed. Therefore, the present study aims at evaluating the individual toxic effects of sodium arsenite (NaAsO2), copper oxide nanoparticles (CuO-NPs) and their joint toxicity on zebrafish Danio rerio. Methodology: Nanoparticles used in the study were characterized for size and morphology using SEM, however chemical composition, surface functional groups and crystallography information were analyzed using EDX, FTIR and XRD, respectively. The adult zebrafish were exposed to these contaminants in four different treatment groups; control group; NaAsO2 (300µg/L); CuO-NPs (1mg/L); and NaAsO2+CuO-NPs (300µg/L+1mg/L). The exposure period consisted of 28 days with samples taken at 7, 14, 21 and 28 days. The fish were exposed in triplicates (n=3) and the organs were obtained through dissection. Total protein content, oxidative stress (ROS and MDA) and antioxidant enzymes (SOD and CAT) were assessed in the gills, acetylcholinesterase (AChE) activity was measured in the brain and DNA damage was evaluated in the liver, histopathological alterations were assessed in skeletal muscles. Result: Both contaminants significantly (p<0.05) increased ROS levels and MDA content, hence inducing oxidative stress in the exposed fish. Whereas the activities of SOD and CAT were inhibited significantly throughout the experiment. Furthermore, the exposure to both contaminants significantly (p<0.05) decreased AChE activity in the brain and synergistic effect was observed in the co-exposure treatment group. The DNA damage was caused by both NaAsO2 and CuO-NPs inducing increase in tail length and movement. Furthermore, histopathological changes including segmental necrosis, degeneration and splitting of muscle fibers, necrosis and shortening of muscle fiber were observed in all treatment groups other than the control group at all sampling intervals. Conclusion: The results of the present study indicate that the combined exposure of NaAsO2 and CuO-NPs leads to a synergistic toxic effect in zebrafish Danio rerio. ix Keywords: Zebrafish, Chronic exposure, Joint Toxicity, Sodium arsenite, Copper oxide nanoparticles, Histopathology, AChE activity, DNA damage, Oxidative stress, Antioxidant enzymes