| Long-term coal mining results in a large number of solid waste-coal gangue.Coal and coal gangue are rich in a variety of harmful or potentially harmful elements,which will release heavy metals into the surrounding environment during accumulation and transportation.Therefore,the accumulation of heavy metals may occur in the soil around the mining area.As heavy metals are toxic,active,persistent,difficult to degrade and bio-accumulate,and easy to migrate to human body through skin,breathing and diet,the pollution of heavy metals has become the focus of attention of the general public in coal mine gangue-soil-plant system.Usually,the migration capacity,biological effects and environmental chemical behavior of heavy metals in soil depend to a large extent on their existing forms.It is of great significance to understand the environmental behavior of heavy metals in the gangue-soil-plant system through in-depth study of environmental media around the mining area,especially the morphology and dynamic changes of heavy metals in rhizosphere soil.In this study,It was taken as the research area.Through the analysis of the concentration and form of heavy metals in gangue,soil and plant around the coal mine area,combined with the analysis of physical and chemical factors of rhizosphere soil,the occurrence forms,bioavailability and influencing factors of heavy metals in gangue-soil-plant system of coal mine area were discussed,and the impact of coal resource mining on the surrounding ecological environment was also discussed.The following conclusions are drawn:(1)The analysis of the concentration and distribution characteristics of heavy metals in the gangue-soil-plant system in coal mining area shows that the average concentrations of Zn,Pb,Cu and Cr in gangue and soil are lower than the standard value for risk control of soil pollution in agricultural land,and the average concentrations of Zn,Pb,Cu and Cr in soybean are also lower than the food limit hygiene standard;the concentrations of heavy metals in different parts of coal gangue hill are different,and the concentrations of Pb,Zn and Cu in the top are relatively high,while the concentrations of Cr in the waist are relatively high.With distance the concentration of heavy metals in rhizosphere soil varies obviously,which can be divided into four types: with distance increasing,the concentration of heavy metalsdecreases,increases first and then decreases,decreases first and then increases,and shows fluctuating changes.The distribution of different heavy metals is also different in organs of soybean.The concentrations of Pb and Zn are relatively high in soybean leaves,while Cr and Cu are mainly concentrated in soybean roots.The concentration of heavy metals was significantly correlated in soybean with that in rhizosphere soil.The enrichment coefficients of Pb,Zn,Cu and Cr in soybean are exponentially related to the concentrations of heavy metals in rhizosphere soil.(2)The morphology and distribution characteristics of heavy metals were analyzed in the gangue-soil-plant system of coal mining area.The results showed that the forms of Zn,Pb,Cu and Cr in gangue and soil were mainly residue;the forms of Zn were mainly residue in soybean,while the forms of Pb,Cu and Cr were mainly extracted by sodium chloride;the concentrations of heavy metals were different in different parts of coal gangue hill,and the forms of Zn,Pb,Cu were different in the top gangue.The main forms of Cr and Cu are residue,and the proportion of Cu and Cr is organic-bound and residue in waist gangue.The concentration of exchangeable heavy metals in rhizosphere soil is higher than that in non-rhizosphere soil,and the concentration of heavy metals does not change significantly with distance in rhizosphere and non-rhizosphere soil.The distribution of different forms of heavy metals is different in different organs of soybean,and the forms of heavy metals are also affected by different physical and chemical indexes in gangue-soil-plant system.(3)The potential ecological risk and risk assessment coding method of heavy metals in the gangue-soil-plant system of coal mining area.It showed that the potential ecological risk of Zn,Pb,Cu and Cr was slight in soil and coal gangue,the RAC value of Zn,Pb and Cr was medium.The availability and environmental risk in rhizosphere soils are Pb>Zn>Cu>Cr.The health risk of heavy metals in soybean seeds mainly comes from Cu and Pb.The target hazard coefficient method shows that the health risk of soybean to children is higher than that of adults in edible mining areas,but this 4.heavy metal elements did not form a high potential health risk and were acceptable.Figure [21] table [32] reference [112]... |
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