Change of available state of Pb, Cd in soil and enrichment and transfer abilities of Brassica chinensis to Pb, Cd as affected by earthworm

As affected by earthworm, the changes of Pb and Cd available states and their contents in soil with different addition amount of Pb and Cd (Pb: 500-1 700 μg · g^-1; Cd: 1-30 μg · g^-1) were studied, and their enrichment and transfer abilities of Brassica chinensis L. to Pb and Cd were also researched. The results show that as affected by earthworm, contents of acid extractable Pb and reducible Pb in soil with addition amount of 500-1 400 μg · g Pb are increased significantly, and total content of available Pb increases gradually with increasing of Pb addition amount in soil. The acid extractable Cd content enhances obviously in soil with addition amount of 5-20 μg · g^-1 Cd and total content of available Cd increases gradually with increasing of Cd addition amount in soil. While earthworm generally has no activation effect on Pb and Cd in soil with addition amount of 1 700 μg · g^-1 Pb or 30 μg · g ^- Cd. As affected by earthworm, Pb content in above-ground part of B. chinensis enhances obviously and Pb transfer coefficients in treatment groups all are higher than those in control groups. And the Pb enrichment coefficient of above-ground and under-ground parts of B. chinensis is 0.037-0.061 and 0.401-0. 628, respectively. As affected by earthworm, Cd content and its enrichment coefficient in above-ground and under-ground parts of B. chinensis are higher than those of control groups in soil with lower addition amount of Cd (1-5 μg · g^-1), while those are lower than those of control groups in soil with higher addition amount of Cd (10-30 μg · g^-1), and Cd enrichment coefficient gradually decreases with increasing of Cd addition amount. And Cd enrichment coefficient in above-ground and under-ground parts of B. chinensis is 1. 196-11.516 and 1.744-20.425, respectively. There is no obvious difference in Cd transfer coefficients between the treatment and control groups. It is revealed that earthworm has an activation effect to acid extractable Pb, reducible Pb and acid extractable Cd in soil, and promotes Pb transfer from under-ground part to above-ground part of B. chinensis, but has no obvious promoting effect on Cd transfer. Moreover, B. chinensis has no obvious effect on Pb enrichment, while has a certain Cd enrichment capability which relates to Cd content in soil.