In this study, the purpose was to investigate the histopathological, genotoxic effect, oxidative stress and cell death due to Metronidazole (MTZ), which is a 5-nitroimidazole compound used widely for the treatment of anaerobic organism infections in fish and humans on gill and liver tissues of Oncorhynchus mykiss.Trout fishes were exposed to 5, 10, and 20 mg/L of MTZ in the aquariums for 2, 4 and 8 days. Staining technics namely H&E, NOS immunohistochemistry, and TUNEL were performed to determine histopathological changes, oxidative damage and apoptosis. Additionally, smear preparations were also prepared from gill blood for genotoxic evaluations. The organ damage started in the 2nd day with 5 mg/L MTZ application and effects increased per duration and dose-dependent manner. It was observed that the gills had the primary and secondary lamellae lengths, with formation of clavate lamellae, fusion in secondary lamellae, separation of epithelium and aneurysm. Regional necrosis, vacuolization of hepatocytes, pycnotic nucleus, enlarged sinusoids were also determined in the liver. NOS immunoreactivity increased with the inducible immunoreactivity (iNOS) that was more prominent when compared to the endothelial immunoreactivity (eNOS). Apoptotic immunoreactivity was higher in the 10 mg 8th day experimental group at liver and gills, and was lower 20 mg 8th day experimental group. When the gills and liver compared with each other, in all doses, immunoreactivity was lower in gills, compared with liver. Genotoxic examinations showed that both number of micronucleated erythrocytes and nuclei abnormalities were higher in MTZ-treated groups.

This scientific article presents the results of studies on the distribution of natural and artificial radionuclides in fish living in the rivers of the northwestern sector of the Arctic zone of the Russian Federation. Fish sampling (about 76 kg in total) was carried out in the White Sea, in the Northern Dvina and Mezen Rivers, and in the Sukhoe Sea Bay of the Arkhangelsk Region, as well as in the rivers of the Nenets Autonomous District: Pesha, Oma, Vizhas, Nes, and Pechora. The results showed the presence of artificial radionuclides Cs-137 and Sr-90 in fish only in the Nes River of the Nenets Autonomous District. The levels of radionuclides in whole bodies perch and pike in the Nes River range from 3.73 to 14.0 Bq/kg wet weight for Cs-137 and less than 3.72 to 23.1 Bq/kg wet weight for Sr-90. In addition to Cs-137 and Sr-90, the presence of the radionuclide K-40, which is the main dose-forming radionuclide, was noted in the fish of all the studied rivers and seas. K-40 activity was in the reached values 138 Bq/kg for whole fish bodies. The only assumption that can explain the presence of artificial radionuclides in the fish of the Nes River is a possible radioactive trace formed as a result of global nuclear tests, including in the Novaya Zemlya archipelago. At the same time, it is noted that the current levels of technogenic radioactivity in fish from the Nes River do not pose a radiological hazard to the local population.

The present study evaluates health risk assessment for inhabitants who are exposed to chromium in fishes and vegetables of the Gulshan Lake. In the fish, chromium concentration has amounted to 2.2 to 149.7 mg/kg, while in vegetables leaf and vegetables stem it has been 5.6 mg/kg and 12.0 mg/kg, respectively. What is more, in sediment it has been 179.5 to 308 mg/kg and in water, 4.0 to 16.9 mg/l. Higher accumulation of chromium (149.7 mg/kg) has been found in a fish species, relatively most affordable for poor people, called Pangas (Pangasius pangasius). Therefore, due to consumption of this fish the resultant non-cancer health hazard indices to people, living nearby Gulshan Lake has been almost 10 times greater than those induced by safe average daily dosages of the respective chemical. Vegetable pathway is still safe in terms of non-carcinogenic health hazard but may be very likely to act as an additive. It is therefore important to immediately take some remedial measures to not only reclaim Gulshan Lake but prevent any further pollution also.