Study Of Ecological Risk Evaluation Of Heavy Metal Pollution At Nickel-copper Mining Area In Jinchang City Of Gansu Province

The nickel-copper mine resources are very rich in the Jinchang city of GansuProvince. Although mineral resources have made tremendous contributions to thedevelopment of local economy, a large quantity of soil degradation caused by heavymetals pollution has posed a serious threat to soil ecosystem.Objective: The purposes of this study are evaluating the ecological risk of heavymetal pollution at the nickel-copper mining area in the Jinchang City, and providingtheory basis for restorating soil polluted by heavy metals.Methods: First, the heavy metal contents of six soil samples (Smelter, Old tailingsdam, Open tailings dam, Gaoanzi, New tailings dam and Xipo) were determined andanalyzed using atomic absorption spectrophotometry and the ecological risks wereanalyzed. Second, the plants were collected and identificated from Old tailings dam,Open tailings dam, and New tailings dam. And the plant species diversities wereanalyzed. The correlation between plant species diversity and heavy metal pollutionwere discussed. Third, the genetic diversities of the microbial community from sixsoil samples under heavy metal pollution were studied by RAPD. Fourth, using theDGGE fingerprint, the genetic diversities of16S rDNA fragments of soil bacteriacommunity under heavy metal pollution were analyzed.Results:(1) In6soil samples, the contents of Cu、Zn、Ni、Co、Pb and Mn all exceeded thebackground values in the local soil, especially Cu and Ni polluted seriously.(2) In6soil samples, the average potential ecological risk trend of the6kinds ofsingle heavy metal in studied areas were:E_r~i(Cu)＞E_r~i(Ni)＞E_r~i(Pb)＞E_r~i(Co)＞E_r~i(Zn)＞E_r~i(Mn). The ecological risk trend of the compound heavy metal pollutionin soil samples were as follows: Smelter＞Old tailings dam＞Open tailings dam＞Gaoanzi＞New tailings＞Xipo. (3) In6soil samples, there was a very significantly positive correlation between thecontens of Cu and Co, Cu and Pb, Pb and Co, and there was a significantly positivecorrelation between the contens of Cu and Ni, Ni and Pb.(4) Thirty plants were collected and identified from Old tailings dam, Open tailingsdam, and New tailings dam, and they belong to12families and29genuses. Theplants at three mining areas were all polluted by heavy metals. The plant speciesdiversity at New tailings dam was relatively high and at the other two mining areaswas low, which may be related with different mining areas polluted by heavy metalsat different degree.(5) There is a very significantly negative correlation between the plant diversityindex and the ecological risk index of Cu, Ni and Co at the mining areas. Thissuggested that the plant diversity at the mining areas was probably influenced by Cu,Ni and Co pollution to a large extent.(6) Peganum harmala L at the Old tailings dam, Tibetia himalaica (Baker) Tsui atthe Open tailings dam, Asterothamnus centrali-asiaticus, Artemisia roxburghianaBess, Echinops gmelini Turcz, and Caragana pygmaea Linn at the New tailingsdam with strong ability of enrichment and translocation to Cu and Ni can beconsidered as the preponderant heavy metal tolerant plants at the nickel-coppermining areas.(7) The genetic diversities of microbial communities were obviously different fromsix soil samples. The relationship between the soil microbial genetic diversity indexand the heavy metal pollution ecological risk index was more complicated, and themicrobial genetic diversity index was not decreased with the increase of heavy metalpollution ecological risk index.(8) The genetic diversities of soil bacteria communities were obviously differentfrom six soil samples. The bacteria community richness was highest at Xipo,suggesting the soil bacteria community structure was relatively stability and lessdisturbed by heavy metals.(9) Using the DGGE fingerprint of16S rDNA fragment and the similarity clusteringanalysis, the similarity coefficient between Smelter and Old tailings dam was the highest at0.68, demonstrating that the effect of soils heavy metal pollution at thesetwo regions to soil bacteria community genetic diversities was relatively consistent.Conclusions:(1)Peganum harmala L, Tibetia himalaica (Baker) Tsui, Asterothamnuscentrali-asiaticus, Artemisia roxburghiana Bess, Echinops gmelini Turcz andCaragana pygmaea Linn with strong potential for recovering seriously pollutedarea could be considered as the preponderant heavy metal tolerant plants at thenickel-copper mining areas.(2)The study of the genetic diversity of soil bacteria community using the DGGEfingerprint of16S rDNA fragment can better conduct early warning for soil pollutedby heavy metal of nickel and copper and assess ecological risk more scientifictly.