摘要 : The fate of the radioisotopes of caesium (¹³⁴Cs, ¹³⁵Cs and ¹³⁷Cs) in the environment depends largely on the extent and reversibility of its adsorption on soil, but there is still debate as to the u... 展开 The fate of the radioisotopes of caesium (¹³⁴Cs, ¹³⁵Cs and ¹³⁷Cs) in the environment depends largely on the extent and reversibility of its adsorption on soil, but there is still debate as to the underlying mechanisms and the best experimental approach to study the processes. The aim of this study was to elucidate the variation of the interaction of a trace amount of ¹³⁷Cs with soil and to find the best methodology to monitor these changes. The loss of ¹³⁷Cs from solution has been monitored over 4 months in soil microcosms at 20 degrees C under both flooded and aerated conditions, and with or without organic amendments (leaf compost or lucerne straw). These treatments were chosen to vary concentrations of potassium and ammonium that compete with Cs for adsorption. We distinguished between spatial heterogeneity within soil aggregates leading to diffusion limitation of adsorption, adsorption kinetics at the soil-solution interface and changes in soil affinity caused by the dynamics of competing cations. The extractability of ¹³⁷Cs by stable Cs was used to probe the degree of fixation. Adsorption was initially under-estimated, caused by equilibration of ¹³⁷Cs within soil aggregates at a sub-millimetre scale. Ammonium produced under reducing conditions in flooded samples and potassium released by lucerne straw inhibited ¹³⁷Cs adsorption by up to a factor of 2. Important differences between samples were masked when soil was suspended in a simple electrolyte solution, thus diluting the competing cations, potassium and ammonium. There was evidence of increased fixation both during incubation and by air-drying leading to up to a two-fold decrease in extraction. Monitoring of dynamics of Cs and competing cations in soil solution provided useful information that was lost when soil was suspended in solution or air-dried. 收起