Heavy Metal Detection In River Sediment And Assessment Of Its Potential Ecological Risk

Heavy metal can cause great harm to the ecological environment and has been an important pollutant in the water environment, because of its toxicity persistence, difficulty to be decomposed and easily to accumulate in aquatic organisms. So it is very necessary to detect the heavy metal content, analysis the pollution condition and distribution characteristics, and discuss the potential ecological risk in sediment. Then a reasonable method should be explored to control the risk.Based on the technology of Atomic Absorption Spectroscopy(AAS), this paper detected the heavy metal content of Cu, Zn, Pb, Cd, Ni and As in water sediment, and also did some research on heavy metal detection method, pollution distribution characteristics and risk control method in Hangzhou Economic & Technological Development Area(HEDA). The main work is as follows.(1) Research of heavy metal detection method in river sediment. The heavy metal contents of Cu, Zn, Pb, Cd, Ni and As in sediment were detected from 18 rivers in HEDA with the traditional method. Then, in order to improve the recovery rate, the detection result of Cu, Zn and Ni under four different digestion systems was studied.Based on the result, the best digestion system of Cu, Zn and Ni in river sediment was proposed, which means a recovery rate of 90% to 110% and the least volume of acid.Result shows that the recovery rate is increased and the total acid consumption of optimal digestion system is in the range of 2~19 ml. And its average acid consumption is 10.54 ml, which is less than the traditional digestion method of 19 ml.(2) Research of spatial distribution characteristics and pollution evaluation of heavy metal in the river sediment of study area. This paper analyzed the heavy metal pollution characteristics of surface sediment and core sediment, and the cluster analysis and factor analysis were used to discuss the heavy metal sources.The results show that the pollution level of Cu, Zn, Pb, Cd, Ni and As follows the order: Cd> Cu>Zn> As> Ni> Pb. Cd and Cu pollution is relative serious. The overall change of heavy metal content with depth is declining in sediment. But it displays irregular changepattern because of different period of human activities and river maintain regulations.The cluster analysis divides 6 kinds of heavy metals into 3 categories. They are Zn and As, Cd and Pb, Ni and Cu respectively, and the heavy metals divided into a categories may have the same pollution sources. 18 sampling sites cluster analysis shows the pollution of heavy metals is relatively uniform. The factor analysis shows that there are three main pollution sources in the study area.(3) Research of heavy metal potential ecological risk and risk control method of river sediment. Hakanson’s Potential Ecological Risk Index was applied to assess the ecological risk of heavy metals in different depth of sediment. Based on the evaluation results, a method named critical risk control was proposed to determine a reasonable environmental dredging depth. The heavy metal polluted sediment can be removed and the potential ecological risk can be controlled in the way of dredging.Results show that the potential ecological risk of Cd is the highest, with the range from 234.2 to 973.3. And the potential ecological risk of Cu in some rivers is medium to higher. According to the critical risk control method, it is calculated that the recommended environmental dredging depth of the18 rivers is 10~110cm.