The Accumulation of Uranium in Agricultural Soils in Kagoshima Prefecture, Japan

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 / m 2 , 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 μ g / g of U, respectively, which showed that these fertilizer materials could become sources of U in agricultural soils. Accord-ing 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 / m 2 in rice paddy fields and 8 . 6 - 9 . 2 mg / m 2 in Chinese cabbage fields per cropping system. These results indicated that the amounts of U input derived from fertilizers per cropping system differed greatly depend-ing on the cultivated crop.