Distributions,Historical Trends And Potential Risk Assessment Of Heavy Metals In Dianchi Lake,China

Heavy metals are distributed in aquatic ecosystems on a global scale. Heavy metal pollutions have both natural and anthropogenic sources in the environment and have become a global environmental issue. Heavy metal, such as lead, zinc, copper, cadmium and chromium, are among the most common pollutants found in industrial effluents. Geochemical structure, mining activity, metal smelting, industrial wastes, incineration of waste and urban sewage discharge create a potential source of heavy metal pollution in the water bodies. Heavy metals are deposited, assimilated or incorporated in water, sediment and aquatic animals since they geochemistry cannot be degraded. They also can accumulate in food chain and become toxic to humans once reach threshold bioavailable levels.Research areas have been included part of the national water quality monitoring sections, eight sites sediment cores and six sites endemic wild fish in Dianchi Lake. Heavy metals are selected as target compounds and their pollution characteristics in Dianchi Lake catchment. The present paper have been deepened the to contamination level, distribution characteristic, historical trend, bioaccumulation and potential risk assessment of heavy metals (Pb, Zn, Cu, Cd, Cr) in water, sediment and three endemic wild fish, carp(Cyprinus carpio), crucian carp (Carassius auratus) and silvery minnow (Anabarilius alburnops), in Dianchi Lake, China. The results obtained served to increase our knowledge of the geochemistry of water, sediment and some endemic wild fish species of the Dianchi Lake, which has remarkable significances in theory, social, engineering application and environmental health.(1) Concentration levels and pollution characteristics of heavy metals in water and surface sediment samples collected from Dianchi Lake were investigated. The results showed that the heavy metals were generally checked out in water and surface sediment and the heavy metals concentrations in surface sediment were higher than their in water. The concentrations of heavy metals in most surface sediments were higher than that in the local background soils. The concentrations of heavy metals in water and surface sediment were in the order Zn> Cr> Cu> Pb> Cd. Compared to other sites (C4:The west of Guanyinshan, C5:Dayuxiang, C6:The west of Haikou, C7:Baiyu, C8:The south of Dianchi), the higher concentrations of heavy metals were observed at north sites of Dianchi Lake (C1:Huiwan, C2:Baoxiang, C3:Luojiaying) that was one of the closest sites to Kunming. This high concentration of heavy metals may be related to urban runoff. sewage outfalls and wastewater discharges at those sites.(2) Pollution characteristics of eight sediment core samples collected from Dianchi Lake were illuminated. Pollution history of heavy metals in Dianchi Lake was investigated. In the sediment cores of Dianchi Lake, the distribution of heavy metals from the bottom to the surface is climb up and then decline or basically constant. The sediment record suggested that concentrations of Pb, Zn, Cu, Cd and Cr have increased significantly since 1970s and have remained broadly stable after 2000s. Pollution history of heavy metals in sediment cores indicating the developmental process of Kunming City, Jinning County and Chengong District around Dianchi Lake.(3) The distribution, bioaccumulation and potential risk assessment of heavy metals were studied in various tissues of three wild endemic fish species from Dianchi Lake. For all sampling sites, the mean concentrations of Pb, Zn, Cu, Cd and Cr in muscle samples were 0.10-0.78 mg/kg dw,21.79-67.87 mg/kg dw,0.48-1.47 mg/kg dw,0.03-0.16 mg/kg dw and 0.13-0.94 mg/kg dw, respectively. The heavy metals accumulated in the three endemic wild fish did not exceed the safety thresholds established by China government departments. At present, the concentrations of heavy metals in fish muscles revealed that fish consumption was safe for human. It was found that the concentration levels were follow the rules of silvery minnow> carp> crucian carp. In addition, the mean concentration in fish organ followed the sequence of liver> gill> muscle. The bioconcentration factors (BCFs) of heavy metal were calculated in fish species ranged from 0.74 to 36.47 and metal uptake was in the order of Zn> Cd> Pb> Cu> Cr. The target hazard quotients (THQ) and hazard index (HI) for heavy metals were below one and did not indicate a danger to the local population. Human health risks associated with fish consumption were not negligible, and the sources of heavy metal pollution in fish clearly should be controlled.