Effects of Ageing and Microbial Component on Chemical Availability of 137Cs in a Long-term Experimental Site
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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.
Keywordsageing leek microbial activity radiocesium ryegrass sequential extraction
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