煤矸石山覆土体系重金属污染特征及生态风险评价

长期堆积的煤矸石会在雨水淋滤、地下水浸泡下释放重金属元素,随着水流向周边土壤扩散的同时,也会在土壤毛细作用及植物根系活动作用下向上层覆土迁移,对土壤质量产生影响。以宁夏宁东某矿矸石山为研究对象,分析矸石山不同深度覆土及周边0~200 m土壤环境中Cu、Zn、Pb、Cr、Cd、As、Mn、Ni元素的空间分布特征,探究土壤环境质量现状,并综合评估土壤生态风险。研究表明:Cr是研究区的主要污染因子,矸石山覆土有86.36%的采样点位Cr含量超过原土,矸石山周边表层、深层土壤分别有100%、50%的采样点位Cr含量超过对照点土壤背景值;煤矸石中有毒重金属元素向覆土有一定的迁移性,且与煤矸石层接触的土壤中重金属元素富集明显;煤矸石粉尘扩散是周边土壤中重金属元素富集的主要途径,其显著影响范围在矸石山10 m内;矸石山周边土壤潜在生态危害指数(RI)为40.80~63.31,污染程度均为轻微,矸石山覆土潜在生态危害指数(RI)为44.83~70.54,仅有1个点位污染程度达到中等。

POLLUTION CHARACTERISTICS AND ECOLOGICAL RISK ASSESSMENT OF HEAVY METALS IN COVERING SOIL SYSTEM OF A COAL GANGUE HILL

Soil covering has been used to isolate coal gangue from oxygen, and it can rapidly remediate coal gangue waste. However, the coal gangue which has long-term piled can release heavy metals under the rain leaching and groundwater soaking, which will diffuse to the surrounding soil with water flow. Meanwhile, the released heavy metals will also migrate to the upper covering soil under the action of soil capillarity and plant root activity, therefore impact soil quality. We chose a coal gangue hill in Ningdong, Ningxia as the research object, and analyzed the spatial distribution characteristics of Cu, Zn, Pb, Cr, Cd, As, Mn, and Ni in the covering soil at different depths of the coal gangue hill and the surrounding soil within 0~200 m distance from the coal gangue hill. We also explored the status quo of soil environmental quality, and comprehensively assessed the potential ecological risks of soils. The results showed that Cr was the main pollutant in the study area. Cr content in the covering soils was higher than the control in 86.36% of the sampling sites, and Cr content was higher than that of the soil background value of the control point in 100% and 50% of the sampling sites of the surrounding surface soil and deep soil, respectively. Toxic heavy metals in coal gangue migrated to the covering soil to a certain extent, and the heavy metals in the soil directly contacting with coal gangue layer were enriched obviously. The coal gangue dust diffusion is the main way to enrich heavy metals in the surrounding soil, and its significant influence range was within 10 m of the gangue hill. The potential ecological risk index(RI) of soils around the coal gangue hill ranged from 40.80~63.31, indicating that the pollution extent was all slight. RI value of the covering soil was between 44.83~70.54, and the pollution extent was of only one sampling point reached the medium level.