The present study assessed the individual and combined toxicity effects of Ag- and TiO2- nanoparticles (NPs) on Ag bioaccumulation, oxidative stress, and gill histopathology in common carp as an aquatic animal model. The 96-h acute toxicity tests showed that TiO2NPs enhanced the toxicity of AgNPs deducted from the decreased LC50 in co-exposure to these NPs. Chronic toxicity tests included a 10-day exposure and a 10-day recovery period. In most cases, histological damages were more severe in co-exposure to Ag- and TiO2- NPs compared with the individual AgNPs however, they were reduced in some cases and also after the recovery period. In co-exposure to Ag- and TiO2- NPs, the Ag bioaccumulation was decreased in the gills but increased in the liver and intestine compared with the singular exposure. After the recovery period, Ag bioaccumulation decreased especially in the liver. Decreased levels of antioxidant enzymes were observed in the AgNPs exposed groups, which were partially alleviated by TiO2NPs. The reduction of condition factor (CF) and hepatosomatic index (HSI) and a severe decrease of weight gain (WG) were observed in co-exposure to Ag- and TiO2- NPs. After the recovery period, the CF and HSI increased but the WG decreased less compared with the exposure period. The present results emphasize the importance of considering the co-existence and interaction of NPs in realizing their bioavailability and toxicity in aquatic environments.
