LAUSR

Despite the wide use of trace metals in various technologies, such as chemical industries and electronic equipment, insufficient information is available on their behavior in the environment. We investigated changes in chemical forms and vertical distribution during the migration processes of trace metals, whose usage is currently increasing rapidly, such as Ag, In, Sn, Sb, and Bi, in soil contaminated with the equivalent of 50–100 times the background concentrations of these metals using an indoor control type monolith lysimeter filled with Andosol during an 8-year monitoring period. The vertical distribution of the total elemental concentrations, the mobile fractions (exchangeable, carbonate-bound, and metal–organic complex-bound) in soils, and the total elemental concentrations in soil solutions were analyzed to study trace metal migration in soil. Except for In, most of the added metals were retained in the uppermost (0–2 cm) soil layer, even after 8 years. However, In markedly migrated downward and accumulated at a depth of approximately 15 cm after 8 years. Furthermore, 10.0 ± 2.9 μg L−1 of In was detected in soil solution at a depth of 17.5 cm. The mobility of In was probably caused by the acidity of the soil, because the pH of the soil between 0 and 15-cm depth was 5 and below, and soluble hydro-oxides, such as In(OH)30aq and In(OH)2+, might be produced at this pH. Consequently, the remarkable mobility of In occurred in Andosol, which strongly retains various trace metals. The proportions of the mobile fractions observed in this study indicated that the mobility of the five metals in Andosol occurred in the order In > Bi ≥ Sb ≥ Sn > Ag.