Effects of Ageing and Microbial Component on Chemical Availability of 137Cs in a Long-term Experimental Site

A loamy soil contaminated with ¹³⁷CsCl 40 years ago was investigated by a sequential extraction technique to determine the effect of ageing on chemical availability of ¹³⁷Cs. The soil samples were sequentially extracted with H₂O, NH₄Ac, NH₂OH·HCl, H₂O₂, and HNO₃. Extractability of ¹³⁷Cs decreased in the order: HNO₃ > Residual > H₂O₂ > NH₄Ac > NH₂OH·HCl > H₂O. Only 0.94% in labile fractions (H₂O and NH₄Ac), while more than 96% was found in the strongly bound fraction (HNO₃ 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 ¹³⁷Cs 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 ¹³⁷Cs in the five cuts by ryegrass was 25% of the labile ¹³⁷Cs in the soil. In addition, a positive correlation was found between the amount of ¹³⁷Cs in labile fractions and that by plant uptake.