Biochemical responses of bivalve mollusk Unio tumidus to the effect of nanoform of zinc oxide depending on the thermal regime

Indigenous bivalve mollusks from the cooling reservoirs of thermoelectric power plants (TPPs) are subjected to constantly elevated temperature and industrial pollution. Therefore, they could be regarded as a suitable model organisms adapted to the combination of typical novel environmental challengers in their habitats. The aim of this study was to elucidate the bioavailability of novel pollutant – nanoform of Zinc oxide (nZnO) – in the mollusks from TPPs depending on the temperature of exposure. The metal accumulation and molecular responses of stress were investigated in the Unio tumidus (Unionidae) mollusks from two cooling reservoirs of TPPs (D- and B-groups) under the exposures to Zinc ions (3.1 µM), nZnO (3.1 µM) at 18 °C, elevated temperature (25 °C), and nZnO at 25 °C during 14 days. In most of the experimental groups, a selective increase of metal accumulation in metallothioneins in comparison with the tissue level, up-regulation of cytochrome c level, and the decrease of oxyradical gene­ration were detected in the digestive gland. In the gills, the increased DNA fragmentation was found. Under the 25 °C, the level of glutathione in the tissues was depleted. B-groups were distinguished by down-regulation of cholinesterase activity and increased level of cadmium in tissues. Thus, the biochemical responses of mussels from the cooling reservoirs reflect the lack of specific mechanisms of detoxification and preva­lence of the nonspecific responses of stress. In the BPP-groups, the signs of toxicity indicate higher level of pollution in the reservoir.