Effect Of Vetiver On Remediation Of Pb,Zn And Cd Toxicity In A Soil And Phytoremediation Lead And Zinc Mining

Phytoremediation is a kind of environment management technique which uses plant to purify, blunt or fix environment contaminants to remove or reduce environment contamination. The vetiveria zizanioides has wide adaptability and strong resistance,which is kind perennial of herb which grows rapidly .There are extensive use in the water and soil conservation,mine rehabilitation,roadway and riverbank protection . Humus is a special compound with high molecule in soil. It has important function in soil fertility and entironment. According to the dissolubility in the acidic and alkaline solution , humus divides into three parts: humic acid,fulvic acid and humin. Humus has many functional groups, such as carboxyl,phenolic hydroxyl,alcohol hydroxyl,ester,ketone group,aether group,aldehyde group and so on. The parts of humus can link to tantalum, clay mineral,oxide,organic pollutants in the soil through hydrogen-bond,Van derW aals foece,ion exchange,ligand exchange .Especially complexing force of humus, it can high efficiency complexation of Pb, Zn, and Cd metal Ione in soil. Pot experiments were carried out to investigate the influence of Cd,Zn and Pb absorption, and utilization by vertiveria zizanioides , and the regulatory mechanism of humus in Pb/Zn mine tailing . The effect of vertiveria ziznioides and root exudates on the heavy metal Cd,Zn and Pb were also study in order to provide theory basis on soil Cd,Zn and Pb contamination phytoremediation .Mixed substrate of humus and NPK fertilizer has been used to restore mine tail- ings in recent years, and Vetiveria zizanioides has been demonstrated to be one of the best choices for revegetation of metalliferous spoils due to its relatively higher metal tolerance. Accordingly, a thorough knowledge of the effect of humus and NPK fertilizer on motility and accumulation of heavy metals in soil-plant system is required so as to estimate environmental behavior of heavy metals and develop revegetation techniq- ues. In this paper, effect of humus and NPK fertilizer on growth and heavy metal acc- umulation of Vetiveria zizanioides on a lead/zinc mine tailings were studied .There were four treatments with four replicates arranged in a completely randomized flowerpot. The treatments included: tailings without any treatment (Treatment A); tailings + NPK fertilizer (Treatment B); tailings + NPK fertilizer + humus (Treatment C); and normal soil (Treatment D).Results presented that the application of humus and NPK fertilizer could provide a cost-effective method for revegetation of Pb/Zn mine tailings, but the transferring heavy metals between tailings-plant system should be concerned. It was found that most of heavy metals accumulated by Vetiveria zizanioides distributed in its roots, and the plant also had relatively higher biomass. Therefore, Vetiveria zizanioides also be a useful plant material for vegetation of Pb/Zn mine tailings.The results showed that vetiveria zizanioides has high accumulation ability to all of the three heavy metals; the metal element contents of vetiveria zizanioides in sequ- ence were Pb > Zn > Cd . The divided contents sequence between leaf and root were root > leaf. The significant relativity in Cd contents of vetiveria zizanioides was found. There was a negative correlation between accumulation coefficient and concentration of metal, and it was the most evident to Cd. The detained percentage of Zn in root was considered as the highest. But to the same metal, with the change of its concentration, the detained percentage is nearly permanent to vetiveria zizanioides.In four different treatment, the concentration of Cd have the same trend in the roots and leaves: B group> A group> C group> D group; The trend of the concentration of Zn in the roots is different to the concentration of Zn in the leaves, the concentration of Zn in the root: Broot> Croot> Aroot> Droot; the concentration of Zn in the leaves : Bleaf> Aleaf> Cleaf> Dleaf; The trend of the concentration of Pb in the roots and leaves : Bleaf> Aleaf> Cleaf> Dleaf, Broot> Croot> Aroot> Droot. As the impact of the biomass of different groups, the concentration of Cd, Zn of the group B are greater than group C in the vetiveria zizanioides, but compared to its total in group C than in group B, and much higher than the other two groups; Roots in group C of the total maximum Pb, while in group B leaves much higher than the total number of other groups, they change the trend: Bleaf> Cleaf> Aleaf> Dleaf, Croot> Broot> Aroot > Droot. This shows that the plant absorption can not be considered only in plant inspection of the total metal concentration, we must also consider the total plant biomass size.It shown the heavy metals Cd, Zn and Pb graded treatment in the tailings, ion- exchange state and carbonate bound form gradually increase throughout the growth cycle of vetiveria zizanioides, which means that heavy metals Cd, Zn and Pb was be activation of vetiveria zizanioides ; it is conducive to the absorption of vetiveria zizanioides.In four different treatment, the resistance index of vetiveria zizanioides who grow in heavy metals Pb, Zn and Cd in the lead-zinc mine tailings is relatively high, the in- dicating vetiveria zizanioides have strong resistance for the heavy metal, especially the presence of humus to heavy metals in the lead-zinc mine tailings resistance performance is especially outstanding.From the cell structure of the vetiveria zizanioides, leaf epidermal cells of vetiveria zizanioides are close, stomatal apparatus is less, and add humus and NPK fertileizers, the number, size and distribution of stomatal apparatus are more obvious change than other treatments. That show the characteristics of drought-resistant plant growth.