Yamaguchi Noriko, Hikono Atsuko, Saito Takashi
Institute for Agro-environmental Science, NARO, 3-1-3, Kannondai, Tsukuba, Ibaraki, 305-8604, Japan.
Hama Agricultural Regeneration Research Centre, Fukushima Agricultural Technology Centre, 45-169 Sukakeba, Kaibama, Haramachi-ku, Minamisoma, Fukushima, 975-0036, Japan.
J Environ Radioact. 2019 Jul;203:18-24. doi: 10.1016/j.jenvrad.2019.02.011. Epub 2019 Mar 4.
Soil amendments with zeolite and vermiculite were expected to prevent radiocaesium (Cs) dissolution and uptake from the soil by plants. In this study, we investigated how zeolite and vermiculite added to soil influence the radiocaesium fixation with ageing. Zeolite and vermiculite were mixed with soil (1 wt%) before or after the addition of carrier-free caesium-137 (Cs) to soils with different radiocaesium interception potential (RIP), which is related to the capacity of the soil to fix trace radiocaesium. Then, the soils were exposed for repeated wet and dry cycles to accelerate Cs immobilization, and its extractability by 1 mol L ammonium acetate was determined before and after 30 dry and wet cycles. Before accelerated ageing (i.e before dry and wet cycles), when Cs was adsorbed on the soil before the addition of the amendments, the addition of zeolite and vermiculite caused a decrease in the amount of exchangeable Cs in low-RIP soils but an increase in the amount of exchangeable Cs in high-RIP soils. The amount of exchangeable Cs was significantly decreased after accelerated ageing regardless of the application of amendments. However, radiocaesium fixation with accelerated ageing was partly inhibited by the addition of zeolite, regardless of the RIP values. The Cs adsorbed on highly selective sites in zeolite is exchangeable by 1 mol L ammonium acetate. Thus, because a portion of the Cs is selectively adsorbed on highly selective sites in zeolite, the redistribution of Cs to frayed edge site followed by ageing-induced fixation was likely limited. However, when Cs was adsorbed on the soil before the addition of the amendments, the addition of zeolite and vermiculite had little influence on the amount of exchangeable Cs. In conclusion, the use of realistic doses of zeolite and vermiculite as agricultural amendments is not effective in enhancing the immobilization of radiocaesium in soil.
人们期望用沸石和蛭石改良土壤，以防止放射性铯（Cs）溶解以及植物从土壤中吸收放射性铯。在本研究中，我们调查了添加到土壤中的沸石和蛭石如何随老化过程影响放射性铯的固定。将沸石和蛭石与土壤（1 wt%）在添加无载体铯 - 137（Cs）到具有不同放射性铯截留潜力（RIP）的土壤之前或之后进行混合，土壤的放射性铯截留潜力与土壤固定微量放射性铯的能力有关。然后，使土壤经历反复的干湿循环以加速铯的固定，并在30次干湿循环前后测定其用1 mol/L醋酸铵的可提取性。在加速老化之前（即干湿循环之前），当在添加改良剂之前铯吸附在土壤上时，添加沸石和蛭石会导致低RIP土壤中可交换铯的量减少，但高RIP土壤中可交换铯的量增加。无论是否应用改良剂，加速老化后可交换铯的量都显著减少。然而，无论RIP值如何，添加沸石会部分抑制加速老化过程中放射性铯的固定。吸附在沸石中高选择性位点上的铯可被1 mol/L醋酸铵交换。因此，由于一部分铯被选择性吸附在沸石的高选择性位点上，铯向磨损边缘位点的重新分布以及随后老化诱导的固定可能受到限制。然而，当在添加改良剂之前铯吸附在土壤上时，添加沸石和蛭石对可交换铯的量影响很小。总之，使用实际剂量的沸石和蛭石作为农业改良剂在增强土壤中放射性铯的固定方面并不有效。
