Pollution of River Ice and prolonged Ecological Risk

In the water ecosystem conversion of organic matter can occur due to various biochemical processes of oxidation, hydroxylation and methylation. Also these may be co-factors which influence on mechanisms of migration and accumulation certain elements in contact zones of water ecosystems (water - suspension particle, water - bottom, water - ice). Researches of ice of the Amur River spent within 2002-2012. It has been installed, that in ices various organic substances and toxic elements accumulate. Thus they are exposed to microbiological transformation. After technogenic accident in Jilin province (China) in November 2005 about 100 tonnes of toxic substances including nitrobenzene, benzene, aniline, chorine-containing substances, polycyclic aromatic hydrocarbons and other volatile compounds came into the Songhua River. The presence of methylated derivatives of benzene in ice may be the result of: firstly, the presence of aromatic hydrocarbons in sewage and waste waters which pollute the river during the ice formation; secondly, biogeochemical processes, which occur in bottom sediments and in the ice mass in winter time. The highest concentrations of methylene chloride and mercury were found in freeze up 2010-2011 in the same ice sample collected from Amur River near to the Khabarovsk city. We carried out the correlation analysis to identify the connecting between methylene chloride and mercury contents. Methylated mercury accumulated in the ice can come into the water of Amur estuary during the ice break-up. Therefore the pollution of the rivers in freeze-up (an ice cover formation) it is possible to observe consequences later 5-6 months (prolonged ecological risk). The layer-by-layer chemical and microbiological analysis of ice, contaminated with organic compounds, may be use to predict secondary pollution of river water with toxic substances during ice melting, as well as to assess ecological risks for hydrobionts of various trophic level.