Phytoavailability Of Heavy Metals In Soils From Leadzinc Mining Area

At the same time when mining activities bring great economic benefits,high heavy metals concentration in soil has negative effects on ecosystems and generate potential health risks to human body.However,the total concentration of heavy metals in soil doesn't represent the fraction available for plants and the toxicty for ecosystems all the time because they accumulate in different geochemical froms.The advantages of chemical extraction methods compaired with a bioassay to determine phtobioavailability in clude the simplicity,reduced time frame,reduced costs,and reproducibility.Despite its enviromental and finacial importance,there is no agreement in the literature as to which extract procedure most accurately estimates the bioavailability of heavy metals and metaloids in soils,and there is lack assessment of enviromental risk of heavy metals pollution of soil based on bioavailability of metals,and there is lack of comprehensive comparison of impactors of phytoavailability,and there is lack of insigts into factors of phytoavailability in micro scal.Inorder to study on phytoavailability of heavy metal in soil proufoundly,a sequence extraction procedure?modified BCR?and two selective single extraction procedures?CaCl₂ and NH₄NO₃?and in suit micro-X ray fluorence spectrometer and synchrotron radiation X-ray absorption near-edge structure spectrometer?XANES?were adopted to analysis species and distribution characteristics of trace metals in soil from Pb/Zn mining area.First of all,combination of data from chemical extractions and the metal quantities that accumulated in maize and darfbean tissues growing on contaminated sites provide the phytoavailabilty in 11 soil samples from three different Pb/Zn mining areas.Pearson's correlation coefficient analysis between the extractable concentration of Zn,Cd and Mn with their concentrations bioaccumulation in plant tissues exhibited a positive significant correlation with diluted CaCl₂ and NH₄NO₃,and BCR F1 is more suitable for Pb.However,the content of water in soils has huge effect on phytoavailability of metals,flooding mainly increased Pb and Mn in garlic shoot and bulb which mainly in reduceble fraction up to 10 times,and decreased Zn and Cd which mainly in acid soluble fraction low to 20%.Second,the soils from the Pb/Zn mining area were contaminated by Pb,Zn,Cd,Mn,33.87%,38.71%,75.81%and 0%of sum samples sites seperately.And total content of heavy metal is not a good indicator of metal phytoavailability,there are only6,4,8,and 3 groups data of content of Pb,Zn,Cd,and Mn in 14 plant tissues correlated with heavy metal total content in soils.And there are 9 groups Pb content in plant tissues correlated with Pb content in soil.The coefficients are 0.99,0.85,and 0.98 between Pb,Zn,Cd in stem of sugar scan and BCRF1 concentration in soils.These results reveal that BCRF1 is a good indicator of phytoavailability of metals.Mn content in sugarscan stem were higher than standard,in agree with enviromental risk assessed by RAC,and differ from the results assessed by EI.The content of BCRF1 has tightest relationship with metal content in plant than pH and OM in soil.Howerver,the effects of rhizosphere can partial transfer Pb from from reducible fraction to acide fraction.?-XRF results indicated that Pb was distributed heterogeneously,and correlated with hot spot with high concentration of Mn.In some special area,Pb also correlated with Fe.It meant that Pb bounded to Fe and Mn oxides.Pb predominantly presented as Pb-goethite?41%-46%?,Pb₃?PO₄?₂?36%-55%?,Pb-humate?1%-36%?,Pb-MnO₂?3%-24%?and Pb?Ac?₂?1%?in soil samples.Results in this study showed that Fe and Mn oxides and coprecipitation as Pb₃?PO₄?₂ are mainly pool for Pb in soils.