Speciation And Enrichment Regularity Of Heavy Metals In Farmland Soil And Earthworm Around Lead-zinc Mining Area

With the development and utilization of mineral resources,environmentalproblems and ecological damage resulting from the exploitation of lead-zinc minebecome more and more seriously. In particular, the heavy metals released by the mineare potentially toxic.They accumulate in soil persistently,and then affect cropgrowth,even transfer to the animal and human body through the food chain. Theseheavy metals from the lead-zinc mine posing significant risk to human health andecological balance. Thus,better understanding for the functions and enrichmentregularity as well as the speciation of the heavy metals play a crucial role in blockingthe toxicity of the heavy metals and improvement of the ecological environment in themining area.Earthworms are able to inhabit and play functionally significant roles in the soilwhich contain exceeding heavy metals and metalloids. Some kind of tolerancemechanisms to the toxic threat of the heavy metals exist in the soil organism.Therefore,study on detoxification mechanisms and metabolic mechanisms ofearthworms play a important role in understanding of the transfer and circulation ofthe heavy metals in the mining area.Lead-zinc mining ares of Nanjing Qixiashan is selected as the study area in ourpresent study.Many biogeochemical samples are collected,such as plants,soil andearthworms.The contents of the plants and soil are determined by the method ofICP-MS and XRF.The element distribution and speciation of the heavy metals in soiland earthworms are investigated by the synchrotron radiation μ-SRXRF andXANES.The information abtained from these methods be used to discuss themigration mechanism and the detoxification mechanisms of the heavy metals in soiland earthworms respectively.There were several conclusions wereached:Firstly,comparing to the standard of soil environmental quality,three gardensin this area are mainly polluted by Pb,Zn and Cu in different degree.Secondly,Fe andMn play an important controlling role in migration and enrichment mechanism ofPb,As,Cu and Zn in the area.Thirdly,through the two-dimensional distribution maps of the elements,chloragogenous tissue around the posterior alimentary canal ofearthworms is the main site for the storage of the Pb,As,Cu,Zn and some other toxicelements.Fourthly,the distribution of Ca is similar with some heavy metals such as Pband Zn in posterior section in earthworms.The distribution characteristics of Ca maybe a specific behavior associated with storage mechanism of the heavy metals inearthworms.Fifthly,even though Pb,Zn,As,Cu and other elements have obviouscharacteristics of common distribution in earthworms,but the storage mechanism ofthe metals are not idential exactly.Sixthly,the best fitting results of Pb form invegetable garden soil is Pb3(PO4)271%andPbS30.4%.Seventhly,the best fitting resultsof Pb form in earthworm is59.8%Pb3(PO4)2and39.2%Pb5(PO4)3Cl.Eighthly,Synchrotron micro-X-ray fluorescence(μ-SRXRF) allow theanalysis of soil in situ at a high resolution as well as maintaining its naturalintegrity,which make it a new effective method for studying the migration behaviorand enrichment regularity of heavy metals in soil.