Denys Sébastien, Echevarria Guillaume, Florentin Louis, Leclerc-Cessac Elisabeth, Morel Jean-Louis
Laboratoire Sols et Environnement, UMR 1120 ENSAIA-INPL/INRA, 2 av. de la Forêt de Haye, BP. 172, 54 505 Vandoeuvre-lès-Nancy, France.
J Environ Radioact. 2003;70(1-2):115-26. doi: 10.1016/S0265-931X(03)00124-3.
Models for safety assessment of radioactive waste repositories need accurate values of the soil-to-plant transfer of radionuclides. In oxidizing environments, (99)Tc is expected to occur as pertechnetate ((99)TcO(4)(-)). Due to its high mobility, leaching of this element in the field might be important, potentially affecting the reliability of estimated transfer parameters of (99)Tc as measured in closed experimental systems such as hydroponics or pot experiments. The aim of this experiment was to measure the leaching of (99)Tc in undisturbed irrigated soil cores under cultivation as well as plant uptake and to study the possible competition between the two transfer pathways. Undisturbed soil cores (50 x 50 cm) were sampled from a Rendzic Leptosol (R), a colluvial Fluvic Cambisol (F) and a Dystric Cambisol (D) using PVC tubes (three cores sampled per soil type). Each core was equipped with a leachate collector at the bottom, allowing the monitoring of (99)Tc leaching through the cores. Cores were placed in a greenhouse and maize (Zea mays L., cv. DEA, Pioneer) was sown. After 135 d, maize was harvested and radioactivity determined in both plant and water samples. Results showed that during the growing period, leaching of (99)Tc was limited, due to the high evapotranspiration rate of maize. After harvest, leaching of (99)Tc went on because of the absence of evapotranspiration. Effective uptake (EU) of (99)Tc in leaves and grains was calculated. EU reached 70% of the input in the leaves and was not significantly different among soils. These results confirmed those obtained from pot experiments, even though leaching was allowed to occur in close-to-reality hydraulical conditions. As a consequence, it was concluded that pot experiments are an adequate surrogate for more complex "close-to-reality" experimental systems for measuring transfer factors.
放射性废物处置库安全评估模型需要准确的放射性核素从土壤到植物的转移值。在氧化环境中，预计（99）Tc以高锝酸盐（（99）TcO4（-））的形式存在。由于其高迁移性，该元素在田间的淋溶可能很重要，这可能会影响在水培或盆栽试验等封闭实验系统中测量的（99）Tc估计转移参数的可靠性。本实验的目的是测量种植条件下原状灌溉土壤芯中（99）Tc的淋溶以及植物吸收，并研究这两种转移途径之间可能的竞争关系。使用PVC管从 Rendzic 淋溶土（R）、冲积性潮土（F）和潜育性潮土（D）中采集原状土壤芯（50×50厘米）（每种土壤类型采集三个芯样）。每个芯样底部都配备了渗滤液收集器，以便监测（99）Tc通过芯样的淋溶情况。将芯样放置在温室中并播种玉米（Zea mays L.，品种 DEA，先锋）。135天后，收获玉米并测定植物和水样中的放射性。结果表明，在生长期间，由于玉米的高蒸发蒸腾速率，（99）Tc的淋溶受到限制。收获后，由于没有蒸发蒸腾作用，（99）Tc的淋溶继续进行。计算了叶片和籽粒中（99）Tc的有效吸收量（EU）。叶片中EU达到输入量的70%，不同土壤间差异不显著。这些结果证实了盆栽试验的结果，尽管淋溶是在接近实际的水力条件下进行的。因此，得出结论认为，盆栽试验是测量转移因子的更复杂“接近实际”实验系统的合适替代方法。
