| 其他摘要 | Heavy metal pollution in mine area and its ecological effect have been increasingly received high concern in environmental geochemical study, particularly for heavy metal pollution in sediment of aquatic ecosystem which may impact significantly on the safety of catchment water environment. The mineral resources occur abundantly in Guizhou Province, and the mining and smelting activities have caused serious heavy metal pollution in the mine areas, particularly for the pollution of thallium (Tl), arsenic (As) and mercury (Hg). The author selects the Lanmuchang Tl mineralized area in southwest Guizhou Province as the study area, and aims to understand the geochemical distributions and behaviors of heavy metals such as Tl, As and Hg in the stream sediment in the mine area, and assess their ecological risks on the local environment. The main conclusions of this thesis are as follows.
1. The concentrations of Tl, Hg, As and Cd are high in the stream sediments of Lanmuchang Tl mineralized area. The average concentrations of Tl, Hg and As in the mine-impacted stream sediment are 23.3 mg/kg, 46.8 mg/kg and 97.3 mg/kg, respectively, which are one or two magnitude higher than their average concentrations of shale. The concentration of Tl, Hg, and As in stream sediments from both the mine -unimpacted area and background area are low. However, the concentrations of Cd are high in stream sediment with an average at 1.31 mg/kg in the mine-impacted area, 1.17 mg/kg in mine-unimpacted area and 1.21mg/kg in the background area, respectively, which are 2-5 times higher than that of shale. The geochemical distributions of Tl, Hg and As in the stream sediment indicate that they are co-source pollutants and are derived from the weathering sulfide minerals from the Lanmuchang mine area. However, the high concentrations of Cd show no obvious evidence of mine source, it may be attributable for the regional geochemical anomalism of Cd. The concentrations of Cu, Cr, Zn and Pb are comparatively low, which are slightly higher than their average concentrations in shale.
2. The calculated geological accumulation index (Igeo) and potential ecological risk index (RI) both show that the local stream sediment of Lanmuchang mine area are mainly polluted by Hg, Tl, As and Cd. The pollutions of Hg and Tl in the stream sediment influenced by the mine are significant and pose high potential ecological risks, followed by As and Cd. The pollutions of Zn, Cu, Cr and Pb are not serious and their potential ecological risks are small.
3 The results of sequential speciation extraction analysis (BCR) of heavy metals in both stream sediment and sediment section show various geochemical distributions for metals. Tl shows both high total concentrations and bioavailable concentrations (6.00 mg/kg in stream sediments and 5.87 mg/kg in sediment sections on average) in the stream sediments, and poses high ecological risk to the environment. The total concentration of Hg is high, but its bioavailable concentrations are low with an average at 0.46 mg/kg in the stream sediment and 1.53 mg/kg in the sediment section, respectively. Thus, Hg poses small ecological risk to the environment. Similarly, the total concentration of As is high but the bioavailable concentrations are low (6.51 mg/kg in the stream sediments and 1.58 mg/kg in the sediment sections, respectively), and the As related ecological risk to environment is also small. Both the total concentration of Cd and the bioavailable concentrations (0.55 mg/kg in the stream sediments and 0.52 mg/kg in the sediment sections, respectively) are high. Therefore, Cd poses high ecological risk to the environment. Neither the total concentration nor the bioavailable concentrations of Cr, Cu, Zn and Pb are low, and they pose lower ecological risks to the environment.
4. The ecological risks caused by the pollution of Tl, Hg and Cd in the stream sediments of the Lanmuchang mine area tend to be mirrored by the direct and/or indirect pollution of metals on the local food chain. Tl and Cd tend to accumulate in the local crops, and Hg tends to be methylated in the local crops as well. The accumulations of Tl, Cd and Hg derived from the stream sediments in the local crops pose high risks to the local public health. |
修改评论