Pollution Assessment And Source Apportionment Of Heavy Metals In Soils Around XinQiao Mining Area In Tongling, Anhui Province

A large number of heavy metals were discharged into the environment during miningand smelting process. As the important containers of heavy metals, soils were heavilypolluted by heavy metals which would cause damages to ecological environment andhuman health if not controlled. The primary task of solving the pollution problem was tosearch out the pollution characteristics and the polluters, so that targeted measures couldbe used to control at fountainhead. In this paper, the surface soils and a soil profile intypical polluted area were taken as the object of the research. Based on analyzing thephysic-chemical properties, heavy metal contents and morphological characteristics, thepollution degree of soils were evaluated around XinQiao mining area. The XRD,SEM-EDS characterization techniques and isotopic tracing technique of cadmium, leadand sulfur were used to search out the sources of heavy metals in soils around miningarea. The conclusions were as follows：Apart from a few soil samples, most samples of XinQiao mining area were acidic; soilorganic matter of all samples was above four levels; the capacity to conserve water andfertilizer of soils around mining area was in medium level. The coefficients for therelationships between pH, cation exchange capacity (CEC) of the soils and the heavymetals were remarkable. The relationships between five kinds of heavy metals alsoshowed a very significant correlation. These relationships indicated that the heavy metalsin the soils around the mining area had the same pollutant source.The surface soils around XinQiao mining area had been seriously polluted by Cu, Pb,Zn, Cd, As. Nemerow Comprehensive Pollution Index showed that mining activities ofXinQiao had caused a serious impact on soils around it, and the pollution contributionrate of Cd was the highest of all. The Geo-accumulation Index showed that miningactivities had resulted in significant accumulation of heavy metals in soils around miningarea, the order of contamination degree of heavy metals was Cd>Cu>Pb>As>Zn. ThePotential Ecological Risks Index showed that Cd was the predominant risk factorfollowed by Cu, Pb, As. The pollution contribution of Zn was very small.Because of mining actives, excess levels of heavy metals had been found in the soilprofile. The relative degree of pollution was in the order of Cd>Cu>As>Zn>Pb. Theactivity of each element in the0～20cm surface soils was significantly higher than thatof deeper soils. The contents and activity of elements reduced with depth increasing.Asthe activity of Cd was the strongest, it could migrate easily in the environment and the ecological harmfulness was the greatest.The speciations of heavy mentals awere varied. The active form of Cd was highestresulting in the highest ecological risk. As had little harm which mainly existed inresidual form. The Fe-Mn oxides form, Carbonate bounded form and organic form of Cu,Pb and Zn were higher, the ecological risks of these elements were controlled byoxidation-reduction condition and pH.The XRD and SEM-EDS characterization techniques showed that there were mineralssuch as pyrite, galena in the seriously polluted soils.Pb isotope tracing research showed that about61.93%～93.26%of Pb in the pollutedsurface soils came from ores. The ratio of206Pb/207Pb in the soil profile increased withsoil depth increasing. The character of Pb isotope in the topsoil(0～20cm) closed to thecharacter of ores.Cd isotope tracing research showed that the soils irrigated by flotation wastewaterwere enrichment of Cd heavier isotopic compositions (the δ114/110Cd ranged from0.05‰～0.24‰) while the soils which were not affected by flotation wastewaterconcentrated lower isotopic compositions of Cd (the δ114/110Cd ranged from-0.02‰～-0.28‰).As a result, pollutant source of the former might be sphalerite, siderite andlimonite etc.; while the latter might come from chalcopyrite, pyrite and galena etc.S isotope tracing research showed that the content and isotopic characteristics of S inthe soils could be affected by mining activities and biological redox and the depth wasless than50cm.