Soil Effective State Of Heavy Metals Combined Determination And Its Phytoremediation

In recent years, with the development of economy and themodernization of agricultural production, the soil heavy metalpollution is worsening, because of waste water irrigation,pesticides, fertilizers unreasonable application, as well as mining,smelting, electroplating and metal processing, chemical and otherindustrial "three wastes" emissions, the quality of soil ecologicalenvironment has been seriously damaged. Once the heavy metalsenter the food chain, it will directly endanger human health.Therefore, the soil pollution with heavy metal is one of the currentglobal concerns on environment. In the early nineteen seventies,scientists have confirmed that the heavy metals of the biologicaltoxicity in the soil depends not only on its total concentration, itlargely depends on their chemical forms in soil, especially dependson their biological availability. The method of chemical extractionwas commonly used for the determination of available heavy metalsin soils. This method is adapted to be used for extracting one and/ortwo elements, and that it spends much time with low efficiency andhigh cost, and it can not function in extracting multiple elementsunlike extraction by joint-agent, so it is not used for efficient detection of soil. While the ASI and M3methods used fordetermination of soil nutrients can extract more elements in soil.Whether it is suitable for the determination of available heavymetals in soil, it remains to be further studied. With the maturationof phyto-remediation technology with low cost since last80years ofcentury, soil pollution control using in situ remediation has becomean important pathway for the removal of heavy metal in soil.Therefore, this technology displays important meaning in theoryand the practice for the study of heavy metals in soil by combiningdetermination.The contaminated soil used in this study was performed byadding heavy metal into soil with artificial simulation method.Firstly, both ASI method and M3method were used to extractavailable Cd, Cr, Pb and Ni in the four kinds of main soil in Northernarea of China (Cinna-mon soil, Fluvo-aquic soil, Brown soil andBlack soil), and the results of determination are compared withother methods including their differences and the extraction rate.At the same time, the Tessier sequential extraction method wasused to study the effects of Cd absorption characteristics on soilmorphology after adding EDTA or not in soils of Linfen suburbs forbetter understanding Cd migration in the soil. A pot experimentswas performed by simulating the Cd contaminated soil (soil inLinfen suburb farm) to study the influence of adding EDTA on plantpurification of Cd pollution in the soil, and the aim for this study is toexplore the role and utilization feasibility of chelating agents afterremoving heavy metals from soil by plants. The main results andconclusions are as follows: (1) Both ASI and M3methods are enable to determine availableCd, Cr, Pb and Ni in soil within the scope of soil heavy metalcontents based on the state standards of the soil environmentalquality, and has very significant linear correlation. M3method has agood relationship in determination of Cd, Cr, Pb, and Ni with othermethods, and is extremely significant with DTPA method, and hasextremely significant and/or significant correlation with NaNO3method excepting available Pb. For the determination of them, ASImethod has extremely significant with HCl method and M3methodhas extremely significant and/or notable compared with HCl methodin cinnamon soil and fluvo-aquic soil excepting available Pb, and themeasured values of effective state Cd, Cr, Pb and Ni are reached thehighest points by M3method. Extraction rates of available Cd, Cr,Pb and Ni in four soil by M3method are different due to different soiltypes, and the proportion of available heavy metal contents in soilsis also different, but all of an effective state Cd, Cr, Pb and Nileaching ratio is maximal by M3method.(2) ASI method, M3method is adept to application fordetermining available Cd, Cr, Pb and Ni heavy metals in Brown soil,and tide soil, Brown soil and black soil in Northern China, and thisresult is similar to that in the actual pollution soil. This method hasan advantage with simple operation, extraction of more elements,as well as decreasing extraction time. Therefore, it is necessary toassess methods on extraction of available heavy metal extraction,and screen an effective combined method for determining multiplestates of heavy metals, and establish an accordingly effective riskassessment mechanism on determination of heavy metal in soil. (3) Before adding the EDTA, soil Cd mainly exist in carbonatebound form, the exchangeable and Fe-Mn oxide-bound theproportion of middle, the organic matter and residual remains theminimum. The three kinds of extractants which extracting Cd fromthe soil, the content in each Cd form is endless different. Afteradding the EDTA, exchangeable Cd content increases, while thecarbonate combined state and the iron and manganese oxidesbound shows declining trend, the other two kinds of morphologicalchange is not obvious; three extraction agent leaching ofexchangeable Cd content increase in various forms.(4) Before the EDTA is added, the increase of Cd concentrationin soil has a small effect on the aboveground biomass of the plant,the amount of Cd the plant uptake is lower relative to exceedaccumulated plant, and doesn't reach the standards as exceedaccumulated plants. The amount of Cd the plant absorbs and soilavailable Cd content was significant positive correlation (P <0.01);with the increase of Cd concentration, the content of Fe in the soilwhere the plants absorb is maximum, the content of Zn, Mn wereunchanged, while the Cu under certain conditions has a trend ofdecrease. With the addition of Cd, the increase of EDTAconcentration, plant aboveground biomass was lower than that ofcontrol and other processing, Cd content the plant uptake shows anupward trend, but still did not achieve the standard whichhyperaccumulting plants uptake Cd, this species has the potentialto purify Cd's pollution of the soil. Zn, Fe content with the EDTAconcentration increased by a big margin, but Cu, Mn, Cd contenthave small changes.