Abstract: Based on historical data and analysis of the samples collected in 2005,distribution and variation of mercury in the surface layer of sediments in the Songhua River were investigated so as to monitor more closely the dynamics of mercury pollution of the Songhua River.A decreasing trend of the mercury concentration in the sediments from the Secondary and the main stream of the Songhua Rivers was observed after the main pollution source was eliminated.Currently,the mercury concentrations in sediments at 18 sections of the river were measured to be quite low,averaged 0.172 mg·kg^-1,and were all at the background level,except for at the sections of Hadawan,Shaokou and Baiqi.A distinct variation was found between the sections in mercury species in the sediments.Hydrogen peroxide-soluble Hg and aqua regia-soluble Hg were the dominant species in the Secondary Songhua River,whereas,acid-soluble Hg and hydrogen peroxide-soluble Hg were in the main stream of the Songhua River.Compared with the 1980s,2005 witnessed a big drop in concentrations of all the mercury species in all the three sections typical of the river,except the aqua regia-soluble Hg.These results demonstrate that the mercury contamination of the Songhua River has been effectively controlled by years of environmental governance and natural purification of the aquatic system as well.

Key words: the Songhua River, sediment, mercury, mercury species, evolution