Silver nanoparticles cause oxidative damage and histological changes in medaka (Oryzias latipes) after 14 days of exposure.

Silver nanoparticles (AgNPs) can exert negative effects on cell lines and embryos of freshwater fish. However, information on their distribution and long-term toxicity in adult species is limited. In the present study, a subchronic (14-d) toxicity test was designed to evaluate the bioaccumulation of AgNPs and their effects on the antioxidant defense system and histology of adult medaka. Purified AgNPs were well dispersed in water, and stability was maintained during the exposure period. After 14 d of exposure, a significant accumulation of Ag in the AgNP-dosed group was observed in the gill and intestinal tissues, with the highest levels found in the liver. Biochemical analysis indicated a dose-related decrease in the activity of lactate dehydrogenase and antioxidant enzymes in the liver, but not in the gills. However, dose-dependent increases in glutathione depletion and lipid peroxidation in the liver and gills were observed. Exposure to a graded dose of AgNPs also resulted in varying degrees of histological lesions in the tissues. Toxicological endpoints combined with metal distribution analysis suggested that AgNPs induced tissue-specific toxicity and that the liver is the organ most damaged by the Ag that might have been released from NPs. The oxidative damage caused by AgNPs may be associated with a large number of histological changes in the fish.