Abstract:

Tianmu Lake,located in Jiangsu Province,is a deeper artificial lake,in fact a reservoir,which is quite different from many large natural shallow lakes in the Yangtze River Delta.It is an import water source for drinking,industry and agriculture in the surrounding area.But,the water quality in Tianmu Lake has deteriorated in recent years.To realize polycyclic aromatic hydrocarbons (PAHs) contamination characteristics in Tianmu Lake,7 surface sediment samples from different parts in the lake were collected in 2006.The concentration of 16 PAHs identified as priority pollutants by the USEPA,were measured by gas chromatography equipped with a mass spectrometry detector (GC/MS).Total concentration of the PAHs ranged from 28750 to 71393 ng/g dry weight,with an average of 458.52 ng/g.The PAH concentration in the surface sediments increased from southern to northern part,indicating that the northern part is in proximity to the incoming PAH source because the tourism industry has been developing rapidly in recent years.The observed PAH contamination levels in Tianmu Lake is lower than those found in river and lake surface sediments in the Yangtze River Delta in China.According to the observed molecular indices,PAHs originated largely from the hightemperature pyrolytic process.A good correlation between TOC content and the total PAH concentration was observed (R ²=0.897 7).Referring to sediment quality guidelines,only the concentration of Fluorene in Sample 1 is more than the effectrange low (ERL) value,but less than the effectrange median (ERM) value,so the toxicity of PAHs in the sediments of Tianmu Lake is relatively low. However,the mean concentration level of total 16 PAHs in the surface sediments is higher than that found in surface sediments of Nansi Lake in the east line of SouthNorth Water Transfer Project.Because of the water exchange period in Tianmu Lake is long,the problem of PAH contamination must be paid much more attention and certain measures should be taken to protect ecological environment of Tianmu Lake.

Key words: Tianmu Lake, polycyclic aromatic hydrocarbon, surface sediment, contamination characteristics