Investigation On Heavy Metal Contaminantion In Soils And Risk Assessment Of Eco-environment In Honggu Coal-Mining Area Of Lanzhou, Loess Plateau In Northwest China

Soil, as one important part of ecosystem, has several useful functions such as removing organic contaminants, cleaning atmospheres and waters. In recent years, heavy metal contamination in soils from emission of "three-waste", irrigation by wastewater, abuse of pesticides, and fertilizers has become harmful to human's health and eco-environment, and has cause the big concern from society. In this paper, soil contamination by several heavy metals and relevant impacts on a typical coal-mining industrial area in Hong-gu, Gansu Province of Northwest China has been investigated by using theoretic statistics through a series of approaches including sample collection from the coal-mining soils, sample analysis in lab and data processing. The present work would be helpful to the establishment of research methods in theory dealing with coal-mining soil contamation, and to the expantion of the research fields of modern soil science. The research results might provide the techniques to reasonably manage soil resources in mining areas, and to solve eco-environmental problems resulted from the decline of soil quality in mining areas.This paper consists of four chapters as:Chapter 1. A Review on heavy metal contamination in coal-mining soilsThis chapter introduced the characteristics and the forms of heavy metals in the contaminated soils, the current developments of contamination by heavy metals in coal-mining soils, as well as the geological environments and the possible reasons. In addition, the environmental impacts of heavy metal contamination in soils, the methods of form analysis and its significance for environments have also been reviewed on basis of 69 references.Chapter2. Experimental schemes and research methods for heavy metal contaminationIn this chapter, Yaojie Coal-Mine of Honggu, Gansu Province in Northwest China was selected as the study area. According to the local natural conditions, the experiments were conducted by using the several methods with the collection of soil samples that were analyed in lab, and the obtained data were processed late on.Chapter3. Comprehensive assessment of soil contamination by heavy metals in the study areaThe enrichments and concentration levels of several heavy metals including Cd, Cr, Co, Cu, Mn, Pb and Zn were discussed with a number of methods including total content analysis, standard comparison analysis, correlation coefficient analysis, and enrichment factor analysis. The results indicated that the heavy metals mentioned above in the study area exhibited the obvious enrichment in the soils, and the concentration levels of heavy metals in the different locatons increased with the history of coal mines and weathering of the tail-minerals. By using 75 surface soil samples collected from the study area, the total concentrations of Cd, Cr, Co, Cu, Mn, Pb and Zn were measured to examine accumulation levels of the heavy metals in coal-mining soils. The results proved that the soils in the study area were, to different extent, contaminated by Cd, Cr, Co, Cu, Mn, Pb and Zn. According to the calculated average pollution indice for single element, the average pollution index was 3.22 for Cd with a range of 2.41-4.19, classifying to the heavy pollution. The average pollution index for Co, Cr, Mn and Pb were 1.47 (1.17-1.90), 1.30 (0,86-1.53), 1.10 (0.95-1.37) and 2.50 (2.04-3.29), respectively. The above mentioned pollutants causesed the slight contamination except for Pb that was classified into the moderate pollution. Furthermore, the integrated pollution index was measured as 2.66, indicating that the soils in the study areas were moderately polluted by the heavy metals.Chapter4. Risk assessment of eco-environment in the study areas contaminated by heavy metals In this chapter, forms, bioavailability and mobility of the heavy metals (Cd, Cr, Co, Cu, Mn, Pb and Zn) in the soils of Hong-gu coal mining were assessed by the modified method of four-steps twice based on the three-steps sequential extraction procedures made by European Community Bureau of Reference. The results were as follows:Cd, that existed as the acid extractable and the oxidable spesies with higher activity, could be bioavailable. Zn and Mn existed mainly as the oxidable form, and could be the free form under a high reduction condition, which had the potential harm for human and crop. These heavy metals are sensitive to environmental variety. In overal, these heavy metals would be released when the changes of pH and the conditions of redox system, so they certainly result in ecological hazards.The form analysis of heavy metals in these areas indicated that the extracactable forms for Cd, Mn, Pb and Zn had the high proportion in comparison with the total concentrations, they had the potential harm to soils in the mining areas. In meantime, Co, Cr and Cu were easily bound on(?)o the soil surfaces due to the less proportion of the activable forms. The results of species analysis also indicated that human activities not only led to higher accumulation of some heavy metals, but also induced the increase of their mobility and bioavailabily, which caused a greater ecological risk by these heavy metals.