The Study For The Crops Of Corn In Lead-Zinc Mine Absorb-transform-store Lead And Their Tolerance Mechanism

High content heavy metals in crops will affect human health directly, studying thedistribution of heavy metals in crops and forms helps to reveal it’s migration andenrichment regularity, to assume the detoxification and tolerance mechanism. It is veryimportant to evaluate the environmental health risk, migration and fate of Pb, at thesame time can provide basic theory data for prevention and control of heavy metalpollution.JINDING lead-zinc mine (YUNNAN) area environment medium was used as theobject of study in this thesis, established a relatively complete experiment method andreliable technical route, the main question is focus on the heavy metal (Pb) absorption-conversion mechanism in the corn from the local farm. First step we using EnergyDispersion XRF (EDXRF) and Inductively Coupled Plasma Mass Spectrometry(ICP-MS) to obtain the concentration of heavy metal Cr、Cu、Zn、As、Cd、Pb in farmlandand plants, then using μ-XRF and XANES to detect the Pb micro area distribution andmorphological. In order to understand the toxic action of contaminant Pb to the corndeeply, we did the tests to know the inhibiting effect about the heavy metal Pb on thesprout, germinal length and root length of the corn seed. The TEM images shown underthe Pb exposure the cell ultrastructure was damaged and the heavy metal Pb cangathering in the root cells. Ultra High Speed Centrifugal seperation-HClO4digestiontechnique was established to detect the content of heavy metal in the subcellularfraction.The elementals analysis have shown that heavy metals in farmland soils aroundJINDING lead-zinc mine at higher levels than limited in the national soils standards.Micro-XRF analysis results have shown that Pb was mainly gathered in the epispermand embryo section in corn seed. This kind distribution was the most toxicity to embryo, thus inhibited the embryo structure in the seed developed into radicle and plumule. Incorn plant, Pb circular distributed in root tissues, the highest Pb was in the stele; Pbcontent in leaf vein was higher than in the blade. The xylem-veins in transmission andretention is a mechanism to adapt to the high Pb toxicity. According to the results ofcorn leaf subcellular separation, Pb content in the cell wall fraction and soluble fractionwas about35%in the total Pb content. A majority of Pb was blocked outside the cellwall and was stored in the vacuole, the two fractions had the similar effect on reduce thePb content in cells.TEM observation found that Pb injured the membranous structures and all theorganelles at different extents. Pb mainly deposited around the intercellular space, cellwall and cell membrane, transport vesicles and mitochondria grana lamella membranestructure also contained few of Pb particles.The Pb-LⅢ(13035eV) XANES spectra of all samples include of root, shoot andthe different part of seed were same, they were same speciation. The main Pb speciationof corn was lead phosphate chloride which deposited inside of corn cell, and a fewcombined with carboxylic to form the organic lead.Based on the results, it is presumed that corn has the ability to translatehigh-activity inorganic lead in the environment to the low migration activity organiclead or phosphate-lead in it’s body, and through accumulation Pb on roots, binding tocell walls, distribution in vacuoles to reduce its content and toxicity in the cell.