LEAD IMMOBILIZATION CHARACTERISTICS IN RHIZOSPHERE SOIL AND POSSIBILITY OF LEAD LEACHABILITY ATTENUAT ION BY COMBINED APPLICATIO OF APATITE AND BUCKWHEAT

Abstract

 Combined application of an apatite immobilizing Pb and a buckwheat (Fagopyrum esculentum Moench) suppressing downward Pb mobility would be useful for sophistication of Pb immobilization technology. The present study evaluated Pb leachability and Pb speciation in the rhizosphere soil on immobilization by the combined application, and discussed Pb immobilization in the rhizosphere soil. The application of apatite decreased Pb leachability and increased the ratio of least soluble fraction in the rhizosphere soil planted for 2 weeks. 37% to 55% of immobilized Pb for 2 weeks after planting was redissolved and the ratio of residual fraction in the rhizosphere soil planted for 6 weeks was decreased in comparison with that for 2 weeks. It was considered that organic acids eluted from the roots have solubilized immobilized Pb. These result suggested that the sophistication of Pb immobilization technology could be possible by amending more apatite into the planted soil, which have a suppressing effect on downward Pb, mobility, than the non-planted soil and taking the suppressing effect of roots on downward Pb mobility into consideration.