Abstract: Acute and sub-acute lethal effects of single and combined Cu,Zn,Pb and Cd on earthworm was determined using meadow brown soil.Results indicated that the mortality of earthworm was significantly related with the concentrations of Cu and Zn in the soil (α=0.05,R_Cu =0.86,R_Pb=0.87),and the inhibition rate of earthworm growth was significantly related with the concentration of Cu in the soil (α=0.05,R_Cu=0.84).There was no significant relation between the concentrations of other heavy metals tested and the death rate and the growth-inhibition rate.The degree of individual earthworm enduring the toxicity of heavy metals varied greatly.The threshold concentration of toxicity defined by statistical method,the level to conduce the death of individual earthworm was 300 mg·kg^-1 for Cu,1300mg·kg^-1 for Zn,1700mg·kg^-1 for Pb,300mg·kg^-1 for Cd.LC₅₀ was 400～450mg·kg^-1 for Cu,1500～1900mg·kg^-1 for Zn,2350～2400mg·kg^-1 for Pb and 900 mg·kg^-1 for Cd.Combined effects of single Cu,Zn,Pb and Cd to conduce more than10% of the death rate of earthworm could result in100% of the death rate of earthworm,thus showing the strong synergistic joint effect of the heavy metals.

Key words: Soil, Heavy metal, Combined pollution, Earthworm, Acute toxicity