2005 Volume 56 Issue 1-2 Pages 9-23
A total of 247 soils collected from the southern to northeastern Kanto district were analyzed for selenium (Se) by continuous hydride generation and atomic absorption spectrometry. The average Se content of volcanic ash soils (0.65 ppm, n=176), brown forest soils (0.47 ppm, n=31) and alluvial soils (0.54 ppm, n=40) are more than ten times higher than that of the average igneous rocks. In the case of volcanic ash soils and brown forest soils, the Se is generally enriched in the upper soil layers than in the deeper ones, and positively correlates with organic carbon and sulfur. This may be mainly caused by the biological accumulation process. The Se rich volcanic ash soils are accumulated during the last 15,000 years, reflecting the global warming and the high biological productivity. Several sand layers derived from basement rocks are found in the cores of alluvial soils. Compared to the mud layers, sand layers are poor in Se, organic carbon and most of the heavy metals. The alluvial soils existed under the effects of saline water in the past tense are significantly dominant in sulfur, but not enriched in Se. This may reflect that Se (VI) does not precipitate with hydrogen sulfide. It has been concluded that the geochemical behavior of Se in soil layers is controlled mainly by the mode of occurrence, biological productivity, redox conditions of environments, and migration during diagenesis.
