Concentrations of lanthanide elements, Th, and U in 77 Japanese surface soils

Abstract

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to measure lanthanide elements, Th, and U in 77 surface soil samples collected from upland fields, paddies, forests, and open areas throughout Japan. The measurements provide an understanding of the background levels of these elements in Japanese soils. The mean concentrations in μg/g for the 77 soils were 18 (La), 40 (Ce), 4.5 (Pr), 18 (Nd), 3.7 (Sm), 0.96 (Eu), 3.7 (Gd), 0.56 (Tb), 3.3 (Dy), 0.68 (Ho), 2.0 (Er), 0.29 (Tm), 2.0 (Yb), 0.29 (Lu), 7.0 (Th), and 2.3 (U). Differences between four classifications of soils based on their utilization were not significant for any measured elements except U. The concentration of U in agricultural soils (upland fields and paddies) tended to be higher than that in open areas and forests, suggesting the possible accumulation of U derived from phosphate fertilizer. Red and yellow soils, which are mainly found in western Japan, have high concentrations of lanthanides and Th. Their high concentrations were mainly attributable to the high concentrations of these elements in granitic rocks, which are the main source materials of these soils. However, red and yellow soils derived from another source material also had high concentrations of lanthanides and Th, indicating that the elements can be enriched during the soil formation process of red and yellow soils even if the source material is not granitic rocks. Andosols, which are derived from volcanic ash, have relatively low concentrations of light lanthanides, Th and U. Concentrations of the elements in peat soils and sand-dune regosols were low. Each lanthanide element in soils had a reasonable correlation with its neighboring lanthanide elements. Thorium and U had correlations with light lanthanide elements. These good correlations might be due to the similarity of their ionic radii.