鹿児島県内の農耕地土壌におけるウランの蓄積実態

抄録

The uranium (U) concentrations of the agricultural and non-agricultural soils in four areas (Isa, Nagashima, Nansatsu, and Osumi) in Kagoshima Prefecture were determined. The U concentrations of the agricultural soils were higher than those of the non-agricultural soils in all areas. The U concentrations were positively correlated with the P concentrations in the soils, which suggested a link between long-term phosphate fertilizer application and U accumulation in the soils. The amounts of U enriched in the agricultural soil surfaces (0-15 cm depth) in the Isa, Nagashima, Nansatsu, and Osumi areas, as calculated from the comparison with the non-agricultural soils, were estimated to be 47-318, 25-343, 61-226, and 47-185 mg/m², respectively. This demonstrated that the accumulation of U occurred in the agricultural soils in these areas. The commercially available superphosphate, magnesium multi-phosphate, fused magnesium phosphate, animal waste composts, and sewage sludge compost in these areas contained 51.6, 22.2, 10.6, 0.88-1.07, and 1.56 μg/g of U, respectively, which showed that these fertilizer materials could become sources of U in agricultural soils. According to the calculation with reference to the amount of fertilizer applied, it was estimated that the amounts of U added from fertilizers were 2.7-3.0 mg/m² in rice paddy fields and 8.6-9.2 mg/m² in Chinese cabbage fields per cropping system. These results indicated that the amounts of U input derived from fertilizers per cropping system differed greatly depending on the cultivated crop.