Effects of ageing and microbial component on chemical availability of (137)Cs in a long-term experimental site.

A loamy soil contaminated with (137)CsCl 40 years ago was investigated by a sequential extraction technique to determine the effect of ageing on chemical availability of (137)Cs. The soil samples were sequentially extracted with H(2)O, NH(4)Ac, NH(2)OH x HCl, H(2)O(2), and HNO(3). Extractability of (137)Cs decreased in the order: HNO(3) > Residual > H(2)O(2) > NH(4)Ac > NH(2)OH x HCl > H(2)O. Only 0.94% in labile fractions (H(2)O and NH(4)Ac), while more than 96% was found in the strongly bound fraction (HNO(3) and residual). However, the activity percentage in labile fractions was increased to 1.34% after autoclaving treatment, while those in the other fractions did not significantly differ. This indicates that the microbial activity played a role in the (137)Cs retention. In the subsequent pot experiments with ryegrass and leek, specific activities in both plants were significantly higher in autoclaved soil than in non-autoclaved soil, and uptake of (137)Cs in the five cuts by ryegrass was 25% of the labile (137)Cs in the soil. In addition, a positive correlation was found between the amount of (137)Cs in labile fractions and that by plant uptake.