Heavy Metals And Ecological Risk Assessment In Water,Sediments And Fish In The Middle And Lower Lancang River

The ecological impacts of hydropower and mining development in Lancang river basin were concerned by riparian countries and international community. In this research, water, sediment and fish samples were collected in the middle and lower Lancang River. Contents of8heavy metal elements within samples were tested by an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) at the laboratory of Yunnan University. Three assessment methods (Potential Ecological Risk Index, water quality compare and Target Hazard Quotients (THQ)) were employed to evaluate heavy metal pollution in the river. The results are shown as follows:(1) Heavy metals distribution in the water of Lancang River was affected by the sample sites and seasonal change. The heavy metals contents in water in dry season (February2014) were higher than those in rainy season (September2014). The contents of Cd, Cu and Zn in Bijiang River water are significantly higher than those in the mainstream. Water quality in the Lancang River is good as a whole, but the contents of Hg in surface water exceeded the Standard of Fishery Environment.(2) Concentrations of heavy metals in sediments along the Middle and Lower Lancang River were influenced by seasonal variation, pollution source and dams’effect. The metal concentrations in sediments were higher in rainy season at Miaowei than those in dry season. The As, Cd, Hg and Zn concentrations in Dalishu’s sediments were higher in the rainy season than those in dry season. Heavy metal concentrations of As, Cd, Hg and Zn at Xiaowan Bridge reach were higher in dry season than those in rainy season, while Cu and Pb showed contrary tendency. The heavy metal contents of Cd, Pb, Hg, and Zn are higher in Dalishu than those at other sections.(3) The concentration of Zn and Cu within fish muscles (Cyprinus carpio) were the highest in all the samples. The concentration of As and Cd in fish samples collected at the junction of Bijiang River and Lancang River were at a low level, however, concentrations of Pb were highest in this reach. The fish caught in Gongguo reservoir contained the highest metal concentration of As and Cd in muscle. The THQ values of As in the Gongguo, Xiaowan and Dachaoshan lakes were2.671,1.825,1.23, respectively. The results indicate that local people would take a healthy risk to eat the fish from the reaches, since the THQ values are over1.(4) The order of heavy metal distributions in sediment, fish and water were sediments> fish>water. Although the concentrations of Hg in all water samples exceeded the standard value, the concentration of Hg in fish muscles did not exceed the food security standard value. The potential ecological risk coefficients related positively to heavy metal in sediments.This study revealed the migration laws of heavy metal pollutants in water and sediments to water ecological system. These results also provide the theoretical supports for development the resources of international river basin.