Sequential extraction was performed for soil samples
from each pot after air-dried (1 g in 40-ml polyethylene
centrifuge tubes) according to the scheme of Tessier et al.
(1979), which is briefly listed in Table 1. After each
extraction, separation was done by centrifugation at
10,000 rpm for 10 min. Lead concentrations in each fraction
were determined by a flame atomic absorption spectrometry
(Hitachi 2000).