Exploring the Interactive Effects of Perfluorooctane Sulfonate (PFOS) and Copper Oxide Nanoparticles in Danio rerio (H.)

Abstract

Background: Perfluorooctane sulfonate has existed in the natural environment for decades, but emergence of novel pollutants, such as engineered nanoparticles, can alter toxicological risks associated to it upon interaction. To understand these interactive toxic effects, this work studies sublethal toxicity effects of perfluorooctane sulfonate (PFOS), copper oxide nanoparticles (CuO NPs), and their mixture on adult zebrafish Danio rerio. Methodology: Nanoparticles used in the study were characterized for size and morphology using SEM, whereas chemical composition, surface functional groups and crystallography information were determined using EDX, FTIR and XRD, respectively. The fish were subjected to four different treatments; control (DMSO 0.03% v/v); CuO-NPs (1mg/L); PFOS (300 µg/L); and CuO NPs+PFOS (1mg/L+300 µg/L). Fish were exposed for 28 days in triplicates (n=3) and from each treatment, 5 fish were randomly sampled at 7, 14, 21 and 28 days and gills were obtained for evaluation of total protein levels, oxidative stress markers (ROS and MDA) and antioxidant enzymes (SOD and CAT). Further, AChE activity was measured in the brain and DNA damage was assessed in fish liver, whereas histopathology of skeletal muscle tissues was also examined. Results: Exposure to CuO-NPs and PFOS in individual and combined settings significantly (p<0.05) increased ROS and MDA content in zebrafish gills, while activities of SOD and CAT were significantly inhibited after 28 days. Induction of oxidative stress and inhibition of antioxidant enzymes was significantly higher in co-exposure treatment. Similarly, both contaminants significantly decreased AChE activity in zebrafish brain which was more pronounced under combined treatment. CuO-NPs and PFOS caused an increase in DNA tail length and tail moment revealing DNA damage, although the highest genotoxic action was observed in the co-exposure treatment. Histopathological alterations including segmental necrosis, degeneration and splitting of muscle fibers, necrosis, shortening of muscle fiber and atrophy were observed in all groups except control on all sampling intervals. Conclusion: Overall, the findings suggest that CuO-NPs and PFOS interact synergistically to cause toxicity in adult zebrafish. Future studies should focus on interactive effects of PFOS and other PFCs with novel pollutants including nanoparticles and distribution of these contaminants across trophic levels under combined exposure. Keywords: Oxidative stress; Nanotoxicity; AChE; DNA Damage; Co-exposure; PFAS; Histology