Study On The Interactions Of Earthworm-Induced Phytoremediation Of Soils Contaminated By Cu And Cd

With the development of industry and agriculture, soil contamination is very serious, restoration of contaminated soil has been become a necessary project to study. Phytoremdiation of contaminated soil has been widely accepted as a cost-effective, envormental-frendly technology. Metal-accumulation plants are usually planted to remove metals from soil by concentrating them in harvestable parts, while the efficiently depends on the amount of aboveground biomass and the bioavailability of metals. Though addition of chelating agents has been shown to increase metal bioavailability and phytoremediation efficiency, it costs too much and shows environmental risk. So, finding a more effective, lower cost and much more safety way to settle the problem of soil contamination is very necessary.Two species earthworm, Pheretima guillemi Michaelsen and Esisenia foelide, Well drained soil ,were used in the acute toxicity test , the object of this experiments was to investigate A dose-effect relationship between heavy metal and its acute toxicity on two species earthworm in soils , calculate LC50 and select earthworm that can tolerate heavy metals. Two soils, Well drained soil and Orthic aquisols were used in culture experiment, were amend respectively to contain 0, 100, 200, 300 Cu mg·kg-1 and 0, 5, 10 and 15 mg·kg-1, Tessler's successive extraction method was adopted to study the main form distribution of Cu, Cd in orthic aquisols and well drained soil. By comparing with treatments with and without earthworm in culture experiment, our object was to investigate the effects of earthworm on heavy metal fraction and bioavailability of plant, to show the mechanisms of earthworm effect on bioavailability of heavy metal, and to provide theoretic base for the application of earthworm in phytoremediation.Toxicity effects of Cu, Cd on earthworms and tissue concentrations of Cu, Cd in the earthworms were determined using Well-drained soil in laboratory. Results indicated that Correlation between tissue concentration of Cd in the Esiseniafoelide and Cd concentration of soil were significant (a=0.05). Tissue concentration of Cu in the Esisenia foelide and Pheretima guillemi Michaelsen increased with Cu concentration of soil ranging from 200 mg·kg-1 to 392 mg·kg-1, and decreased ranging from 392 mg·kg-1 to 1075.6 mg·kg-1. Thetissue concentration of Cd in the Pheretima guillemi Michaelsen increased with Cd concentration of soil ranging from 200 mgkg-1 to 548.8 mg kg-1, and decreased ranging from 548.8 mg·kg-1 to 1505.8 mg·kg-1. LC50Cu of Esisenia foelide and Pheretima guillemi Michaelsen is 387~555 mg·kg-1 and 412-653 mg·kg-1, respectively. LC50cd of Esisenia foelide and Pheretima guillemi Michaelsen is 809-1138 mg·kg-1 and 708-1030 mg·kg-1, respectively. It is concluded that Pheretima guillemi Michaelsen s tissue concentration of Cu and endurance is higher than that of Esisenia foelide, but Esisenia foelide's endurance for Cd is higher than that of Esisenia foelide, and it's tissue concentration is lower than that of Pheretima guillemi Michaelsen.In Cu added treatment, Cu exacted by NaAc and H2O2-HNO3 were the main species in Orthic aquisols, while Cu exacted by NaAc and NH2OHHCl in Well drained soil. In Cd added treatment, Cd exacted by MgCl2 and NaAc were the main species in Orthic aquisols, while Cd exacted by MgCl2 in Well drained soil .Compared to Orthic aquisols, Well drained soil has the obviously higher content of MgCl2-exacted Cd and the same content of NaAc and NH2OHHCl-extracted Cd. The growth of Sorghum Hybrid Sudangrass can be inhabited in this two soils with Cu added, but can been improved in low concentration with Cd added and inhabited in high concentration with Cd added. The Cu, Cd added have high effect to the biomass of Sorghum Hybrid Sudangrass in Well drained soil compared to that in Orthic aquisols. NaAc-extracted Cu in Orthic aquisols and NH2OHHCl-extracted Cu in Well drained soil and MgCl2-extracted Cd in those two soils have high effect to the adsorption of Cu and Cd by Sorghum Hybrid Sudangrass. Sorghum Hybri...