Environmental Biogeochemistry Of Heavy Metals In Different Mediums In Dumping Sites Of Coal Mine Spoil In Huainan

The coal mine spoil is an evitable byproduct in the process of coal mining. It is estimated that discharge of coal mine spoil takes up10-25%amount of coal mining and that increasing speed is about10%in China. During the process of opencast and underground coal mining, lots of coal mine spoils are excavated and deposited nearby as coal waste piles. When pile exposed to atmospheric conditions and undergone accelerated weathering, some adverse effects may occur during its formation, such as arable land occupation, AMD effluent, spontaneous combustion, vegetation deterioration and so on. Toxic element released from the coal mine spoil during the process of leaching, weathering and spontaneous combustion would accumulate in lots of different environmental mediums surrounding the coal waste pile. The heavy metals would transfer through the food chain or food net. People resided in dumping sites of coal mine spoil may be posed potential health risk resulted from heavy metals accumulation. Therefore, it is necessary to depict out the distribution and transferring of heavy metals in different environmental mediums in this area to manage the ecological risk for the safety and health of the people. In this research, three coal waste piles were chosen to be investigated. Heavy metals concentrations in different mediums and chemical properties of soil and coal mine spoil were analyzed. Vegetation distributed at the bottom of coal waste pile was also investigated. Then the aims of this project were focused on:(1) the characteristics of heavy metals’s distribution in different mediums (coal mine spoil, soil, water, rice, soybean, earthworm and fish);(2) potential health risks posed by the heavy metals in different mediums;(3) the distribution and limiting factors of vegetation developed on coal waste pile and (4) the possibility of earthworm resided in dumping sites of coal mine spoil to be taken as bionidicator or bioconcentration of heavy metals in soil.Through research, main results were summed as follows:(1) Mean concentrations of heavy metals in different mediums were lower than the corresponding limit values proposed by China National standards. Mean concentrations of Zn, Pb, Cd, Ni, Cr and Cu in coal mine spoil and soil were under level one of National Soil Environmental Quality. Mean concentrations of Zn, Pb, Cd, Cr and Cu in the grains of rice and soybean and the muscle of fish were lower than Tolerance limit of heavy metals in foods. Mean concentrations of Zn, Pb, Cd, Cr and Cu were also within level two of Environmental Quality Standards for Surface Water. Besides, concentrations of heavy metals in different mediums varied with the deposition time. The variation of heavy metals was not identical in different mediums.(2) Heavy metals distributed differently in different mediums. Concentrations of heavy metals in coal mine spoil varied with the height. Concentrations of heavy metals in surface soil (0-20cm) varied with the distance, which could be sorted into two types: concentrations of heavy metals decreased with the distance, and concentrations of heavy metals increased first and then decreased with increasing distance. Heavy metals also distributed differently in rice and soybean. Concentrations of heavy metals in rice and soybean didn’t significantly correlate with heavy metals contents in soil. When absorbed by rice and plant, heavy metals also promoted or inhibited with each other. The relationship for bioconcentration factors of Zn, Ni, Mn and Cu in rice and soybean to that concentration in soil could be described by Power exponent equation. The viscera and gill of fish were the dominant organs for heavy metals accumulation, while flesh, scale bone, fin and swim bladder were less accumulated by heavy metals. Heavy metals was also promoted or inhibited mutually in fish.(3) Vegetation analysis showed that heavy metals concentrations in coal mine spoil were in normal range, which did not affect the resident of pioneer plant (take Xinzhuangzi coal mine as an example). Elevated levels of salinity and pH, low levels of total P and total K might be the inhibiting factors for restraining the residence of plants on coal waste pile. It was also founded that Synodon dactylon and Erigeron bonariensis.L were the dominant plants in local stable plant communities and could be used for restoration of coal waste pile in the near future.(4) Some relations were found between the heavy metals concentrations in earthworm and soil. Concentrations of Zn and Cd in earthworm could accurately indicate the concentrations of Zn and Cd in soils, while the concentrations of Ni, Cr and V could signify the distance between the earthworm sampling site and the coal waste pile. As the bioconcentration factors for Zn and Cd in earthworms were above1, it suggested that earthworm could accumulate Zn and Cd in soil. Therefore, earthworm could be used as a biological indicator for Cd and Zn in the soil in dumping sites of coal mine spoil. (5) Environmental risks posed by heavy metals in different environmental mediums were at low levels (except the risks of carcinogenic chemical caused by Cr in rice, soybean, water and fish). The potential ecological risks posed by heavy metals in coal mine spoil and soil were at light levels. That risk decreased in coal mine spoil and increased in soil when varied with deposition time. The health risks of carcinogenic chemical in rice, soybean, water and fish were mainly posed by Cr. Cr posed much higher risk than Cd as well. The total person health risks per year in rice, water and fish were at moderate levels and the total risk in soybean was at acceptable level (except in middle aged coal mine).