The Effect Of Earthworm Eisenia Foetida On Pb-polluted Latosol

By the methods of adding Pb into unpolluted Granitic latosol in Hainan with different level(0,50,100,200,400,800 mg/kg), cultivating earthworms(Eisenia foetida)in the polluted soil(30d,60d), we had studied the effect of earthworm on content of various Pb forms, hydrolyzable nitrogen, available phosphorus, available potassium, organic matter and pH. The research results as follow:1. The results from the test of Pb toxicity to indicated that the earthworms were not poisoned in low concentration of Pb(200 mg/kg Pb+sand), but they were hurted by high concentration, and appeared escape, convulsive, curl, skin rash, produced capillary and secretion matter. It was very different for the earthworms to the concentration of causing die. Pb concentration of half causing die(LD50) in liquid, sand, soil and cow dung were 354.41 mg/kg,360.95 mg/kg,1228.02 mg/kg and 3894.62 mg/kg, respectively.2. The earthworm had a good endurance to Pb in cow dung. It still could survive when the concentration t of Pb reached 15,000 mg/kg. The earthworm could live normally when the concentration of Pb was lower than 6,000 mg/kg. Pb could reduce the weight of earthworm in the high concentration condition(9000,12000,15000 mg/kg).3.The earthworm could accumulate Pb in the low concentration(Pb<200 mg/kg). the earthworm could absorb more Pb when the concentration of Pb was increasing in soil when the Pb concentration reached 200 mg/kg, the enrichment coefficient was 3.44. High concentration of Pb (400,800 mg/kg)could reduce the earthworm to absorb Pb. The various Pb forms could increase total Pb in earthworms, the order were amorphous iron oxide bound Pb > residual Pb >exchangeable Pb > organically bound Pb > MnO2-bound Pb > carbonate bound Pb > crystalline iron oxide bound Pb .4.The pollution of Pb in soils would restrain the earthworm recovery and growth rate, after 60d culture, especially in the concentration of 400 mg/kg and 444 mg/kg ,the earthworm,s recovery and growth rate were 0.6403 and -0.4358. The earthworm could live normally when the Pb concentration was lower than 400 mg/kg, and we should add cow manure when the concentration of Pb was higher than 400 mg/kg. The various Pb forms could restrict weight increase rate of earthworms. The order were carbonate bound Pb> exchangeable Pb > organically bound Pb > MnO2-bound Pb > crystalline iron oxide bound Pb> amorphous iron oxide bound Pb > residual Pb5.The earthworm could enhance mineralization of organic matter and improve the quantity of hydrolyzable nitrogen and available phosphorus in the Pb added soils,but it had no remarkable effect on available potassium and pH. In 30d, earthworm could not affect the content of various Pb forms, but it could decrease the concentration of residual Pb, and increase the concentrations of exchangeable Pb and amorphous iron oxide bound Pb. In 60d, carbonate bound Pb, crystalline iron oxide bound Pb, organically bound Pb, amorphous iron oxide bound Pb and MnO2-bound Pb had not remarkable change in the experiment. It could be concluded from the studies that Eisenia foetida was able to improve Pb-polluted soil.