LAUSR

The toxicity effect of nanoparticles when exposed to other environmental pollutants is not completely known. Therefore, the aim of this study was to evaluate the effect of coexisting mercury chloride (HgCl2) and silver nanoparticles (Ag-NPs) on the oxidative stress response, behavioral pattern, and histopathological changes of goldfish. In this study, goldfish (Carassius auratus) with mean length of 5 ± 0.4 cm and mean weight of 3 ± 0.3 g were assigned randomly to four experimental groups (15 fish in each group); exposed to a non-lethal concentration of Ag-NPs, a non-lethal concentration of HgCl2, a mixture of Ag-NPs and HgCl2, and a control group. In the end of experiment, activities of antioxidant enzymes (SOD, CAT, GPx, TAC, and MDA), bioaccumulation of Hg, and histopathological alterations in gill and intestine tissues were studied. Intensity of histopathological anomalies in goldfish tissues when HgCl2 and AgNPs mixed group was higher than the anomalies observed in HgCl2 or Ag-NPs nonlethal concentration. Aneurism, hyperplasia, fusion of lamellae in gills and degeneration, increase in the number of goblet cells and swelling of goblet cells in intestines were observed as notable damages in combined group. Moreover, co-exposure of HgCl2 and Ag-NPs significantly curtailed the length of secondary lamellae (p < 0.001) but increased the diameter of primary and secondary lamellae (p < 0.001). We observed significant differences in the mean activities of GPx, CAT, and concentrations of TAC and MDA in gills between experimental groups (p < 0.05). No significant differences between groups in the mean activity of these parameters (except for MDA) were found in intestines. Compare to HgCl2 and control groups, Hg bioaccumulation was significantly higher under HgCl2 and AgNPs mixed group (p < 0.05). We conclude that in the sub-acute term, simultaneous presence of silver nanoparticles and mercury in the aquatic environment can induce a synergistic effect on goldfish tissues. © 2018 Desalination Publications. All rights reserved.