Abstract: In this study, we evaluated the efficiency of remediation of two kinds of Cd contaminated soils (fluvo-agvic soil in Henan Province and cinnamon soil in Hebei Province) by earthworm (Eisenia fetida) in pot experiment, taking into consideration the rate of Cd reduction in wheat grain, bioavailable Cd in DTPA-extracted fraction and rate of Cd removal from soil. The results showed that Cd uptake by wheat was significantly reduced by the application of 0.5% or 1.0% earthworm(live earthworm over dry soil). Compared with control, the addition of earthworm resulted in an increase of wheat yield by 35.5%62.7%, while the rate of Cd reduction in wheat grain ranged between 31.1% and 43.5%. We believe the decreased Cd uptake and re-distribution of Cd in wheat due to earthworm were responsible for decreasing Cd content in wheat grain. The 0.5% and 1.0% earthworm could significantly reduce the soil DTPA-Cd concentration (P<0.05) by 29.1%40.8%, benefiting the transformation of Cd from bioavailable to solid forms. The removal rate of soil Cd (6.05%11.88%) was much higher than that found in the control (P<0.05), indicating earthworm has excellent potential in remediation of Cd contaminated soil. In conclusion, adding low concentration of earthworm to Cd contaminated soil played an important role in lowering Cd soil content and Cd uptake by wheat and wheat grain, which is of great significance for remediating Cd contaminated soil while ensuring the safety of agricultural products.

Key words: Cd, earthworm, rate of Cd reduction in wheat grain, DTPA-Cd, rate of Cd removal from soil