| Heavy metal has characteristics of strong toxicity,easy accumulation,non-degradation and so on,which has attracted much attention in the environment.The main gathering place of heavy metal is soil and sediment,so it is of great significance for exploring the source of heavy metals and evaluating its pollution status that study the content and temporal distribution of heavy metals in soil and sediment.Earthworm compost has the characteristics of low cost,high safety and no secondary pollution,and the compost products have higher humus and organic matter and have good adsorption properties.Therefore,earthworm composting products can be widely used in controlling heavy metals and other pollutants in soil and sediments.This study researched the soils and sediments in 15 sites in the typical area along the coast of east Dongting lake in China.Multivariate analysis methods employed in this research included two-dimensional hierarchical clustering analysis(2-D HCA)and principal component analysis(PCA).Nine prominent heavy metals of Dongting lake were selected as monitoring factors:As?Cd?Cr?Cu?Fe?Mn?Ni?Pb?Zn.We discussed the major sources and the spatial distribution characteristics of heavy metals according to the result of 2-D HCA.The results showed that the accumulation of As,Cd,Mn and Pb in soil and sediment was obviously influenced by human activities,while Cr,Fe and Ni were mainly derived from maternal materials.The result of principal component analysis suggested that heavy metals in soils were positively correlated with pH and total phosphorus(TP),and in sediments,As,Cr,Fe and Ni were closely related to pH and cation exchange capacity(CEC),while Pb,Zn and Cd played a positive correlation with total nitrogen(TN),total phosphorus(TP),total carbon(TC),moisture content(MC),soil organic matter(SOM)and loss on ignition(LOI).Soil leaching is a kind of technology with enormous developmental potentiality to remove soil/sediment heavy metal pollution.This paper adopted the experimental method of soil column leaching,employed the simulated acid rain as soil drench lotion,used the worm composting product as adsorption material,explored the changes of pH,electrical conductivity(EC)and organic carbon(TOC),humus composition factors in the process of leaching study.Through these changes to analyzed the adsorption effect of composting material on heavy metals and influence factors.The sediment used in the column experiment has been aged by 4mg/g Pb?0.4mg/g Cd?4mg/g Cr.The comparison with the blank group showed that the adsorption effect was best when the adsorption material was located at the bottom of the soil column,and the average adsorption capacity of Pb,Cd and Cr can reach 90%,97%and 75.5%respectively.We can conclude that the earthworm composting products have a strong adsorption effect on Pb,followed by Cd and then Cr.According to the change of physicochemical properties,pH of the leachate had an obviously promotion and TOC decreased clearly when the composting material was placed at the bottom of the column,and the spectral intensity of fulvic acid also showed a visibly decrease.In addition,when composting material was placed at the middle of the column or mixed with sediment,the pH of the leachate also had a promotion,and TOC and EC were also reduced in different degrees.The results fully showed that the increase of pH had a positive role in heavy metal adsorption,and the complexation of fulvic acid and heavy metals played an important role in the process of adsorption.Other organic components in sediment also had a varying degree of adsorption on heavy metal ions,resulting in a general decrease of TOC in leachate. |
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