| Soil is one of natural resources and plays an important role in agriculturalproduction; normal function of the soil ecosystem is required by thesustainable development of agriculture. With the rapid development ofeconomy and increment of "three wastes" of industries, the soil iscontaminated differerntly. With the characteristics of hard mobility, long timeof retention and indecomposability of heavy metal ions, heavy metalcontamination in soil is related to not only the total amount of heavy metalsbut also its different forms in the soil environment; Different existing forms,different activities, toxicities and migration characteristics. According to thepresent antimony polluted situation of Qinglong antimony mine areas,research work about the soils around typical metal mine pollution was carriedout. Taked the farmland soil around an abandoned antimony smeltery namedDachang in Karst mountainous area of Qinglong County in Guizhou provinceas an example, heavy metal content in surface soil and typical soil profile ofdifferent distances away from smelter chimneys was determinated thoroughlythrough field investigation and laboratory analysis, and contamination ofheavy metal in soil was evaluated by the methods of Nemerow Compositepollution index, geoaccumulation index and potential ecological risk index;health risk assessment of primary agricultural products in this area was alsostudied according to heavy metal concentration. The results are showed asfollows: (1) The mean concentrations of Sb, Zn, Pb, Hg, As and Cu in surfacelayer soils were58.58,11.96,7.99,7.45,6.70and1.60times of soilbackground values of Guizhou, respectively. The vertical variation of heavymetals except Pb in soil profiles were significantly different and the averageconcentration of heavy metals in soils was followed the sequences:Mn>As>Sb>Cu>Cr>Pb>Hg>Cd, which were all higher than the average levelof the national soil background value, and moreover, the average conentrationof As, Cr, Mn and Hg performed to have great differences, the main pollutionelements Hg and As were4.7times and4.4times of the standard of nationalgrade II, followed by Cd and Cu which were3.0times and2.7times,respectively.(2) Correlation analysis and cluster analysis showed that the soil wassuffered from cotaminnation of kinds of heavy metals, such as Cr, Cd, Cu, Sband As, which were all higher in all layers of soil profile and the top-layer(0-20cm) in the light of SFPI. However, certain risk to plant was presentedaccording to the assessment results of heavy metals with Single FactorPollution Index(NCPI). The pollution levels were followed the sequence:Dachang village>Zhongxinjie village>Bikang group and Tianba group, andthe index was between1.21and14.83.(3) Due to the long history and intensive mining and smelting activities,the mean concentrations of Sb and As in surface layer soils were seriouslyhigh; for example, the concentation of Sb was reached5.0mg/kg. Compared with the soil background values in Guizhou, the concentrations of Sb and Asand Bi were extremely significant difference (P<0.01). Chemical fractions ofSb and As and Bi extracted by0.11mol/LCH3COOH showed that theconcentration of Sb and As and Bi from high to low in turn was Sb>As>Bi.The concentration of Sb in the drinking water of Huang Jia Dong which comesfrom an underground spring was safety according to the reference standard.The pollution levels of Sb and As and Bi in Dicranopteris pedata and Imperatacylindrica which can be used to accumulate heavy metals were followed thesequence leaves>root. The relative bioavailability of As in Polygonumcapitatum Buch.-Ham.exD.Don was significantly higher than Sb, and it is alsocan be used to remove metals from contaminated soil.(4) With the different patterns of land use, concentation of Sb in soils wasfollowed by the sequence: maize field>chilli field>soybean field> unused field.All data are quoted from the original sources, and the concentrations of Sbwere significantly higher than the background levels in Guizhou Provincesoils (p<0.01).The average concentration of total Sb reached136.22mg/kg insoils of maize field in the study areas, with a range from13.47to326.60mg/kg.The pollution of Sb in different direction caused by Sb smelting was different,and the pollution in soils were followed the sequence: east>north>west>south;and the concentration was200.08mg/kg,154.92mg/kg,148.45mg/kg and79.48mg/kg, respectively.(5) Chemical speciation of Sb in the surface layer of maize field was studied based on the reformative BCR sequential method. Sb in soils mostexists in an residual fraction, and next was reducible fraction and watersoluble, and third was acid soluble and oxidizable fraction, while the contentof acid soluble and water soluble which can be absorbed by root was prettylow, which account for1~3%of their content. The biological activitycoefficient mean value of Sb was4.23(range from0.63to8.75), and the rangeof potential Sb that could be absorbed by crops was2%~13%.(6) Content of Sb in different organs of maize was followed the sequence:root>stem>leaf>seed; The average biological accumulation coefficient wasfollowed the sequence: root>stem (=leaf)>seed; The biological transfercoefficient mean value of Sb was1.16(range from0.50to4.31). Theaccumulation of Sb ability in aboveground maize was higher than roots, andthere was no obvious correlation between them. Therefore, returning straw tofield can not be used as soil fertility for the content of antimony exceeded thereference values (taken50μg/kg for maximum) in every organs of maize, andit is risky to take maize crops as forage too. |
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