煤层气生产区重金属污染特征及其潜在生态危害

Heavy metal pollution feature analysis and potential ecological risk assessment of the coalbed methane production on the topsoil qaulity of the mining area

为了调查煤层气生产区采出地层水中的重金属在露天排放下对生产区地表土壤的影响,采集生产监测区煤层气井产出地层水样、蓄水池积水样、蓄水池底泥样和井场周围地表土样进行重金属含量的测试分析,应用地质累积指数法和Hakanson潜在生态危害指数法对地表土壤的重金属污染程度和生态危害进行了评价。结果表明,煤层气生产区井场蓄水池底泥受到As、Cd、Sn的中度污染,周围地表土壤受到Cd、Sn的中度污染和As、Cr、Pb、Cu、Co的轻度污染,各重金属的污染程度由高到低为Sn、Cd、As、Pb、Cr、Co、Cu、Mn、Ni、Zn。煤层气生产区土壤中重金属存在中度的潜在生态风险,对煤层气生产区地表土壤生态环境产生潜在生态风险的最主要重金属是Cd。

The paper is aimed at bringing about its heavy metal pollution characteristic feature analysis and assessment of the eco-environmental risk of the coalbed methane production on the topsoil qaulity of the mining area. We have chosen the water-formation samples, the hydrops samples of the tanks, the sediment samples of the tanks and the topsoil samples around the coalbed methane well to investigate the impacts of heavy metal polluted water on the topsoil quality of the coalbed methane production area under study. We have also determined the geo-accumulation index and Hakanson potential ecological risk index for evaluating the pollution degree and the potential eco-risk from the heavy metals in the said production area. The results of our investigation and analysis show that the heavy metals from the production polluted water has been migrating and enriching the sediment contents of the water sediment. The concentration of the heavy metal Cr from the water pollutant and the hydrops samples of the tanks have been found obviously exceeding the standard concentration of the surface water environmental quality. The concentration coefficient of the most heavy metals from the sediment samples of the tanks and the topsoil samples around the coalbed methane well sites has been found greater than 1, which is beyond the natural background value of those heavy metals in the soil. The sediment of the tanks has been suffering a moderate pollution from As, Cd, Sn. It has also been found suffering a moderate pollution from Cd and Sn, as well as a mild-level pollution from As, Cr, Pb, Cu, Co. Thus, the pollution degree of different heavy metals follows the following descending order： Sn〉Cd〉As〉Pb〉Cr〉Co〉Cu〉Mn〉Ni〉Zn, which indicates that the potential ecological risk index of Cd should be standing between 80 and 160. Thus, it can be seen that the potential ecological risk brought about by the risk index of the chief heavy metal Cd belongs to the severe level, with the contents of other heavy metals show a slight potential ecological hazard. On the whole, the degree of potential ecological risk from heavy metals in the coalbed methane production area of the mine belongs to the medium level. Therefore, Cd proves to be the number one heavy metal pollutant that contributes to the potential ecological risk on the topsoil environment of the coalbed methane production area.