A long-term study of selenate sorption in Finnish cultivated soils

Abstract

The behaviour of added selenate was investigated in a long-term study with 18 cultivated Finnish soils in vitro. In addition to the physico-chemical properties of the soils, the aerobic activity, measured as the production of carbon dioxide, was taken as an independent variable. In an incubation experiment the selenium sorption of 16 quadruple soil samples was successful. According to the behaviour of selenate four groups of soils were identified as follows: (1) where the sorbed fraction increased during the whole experimental period (three soils); (2) where the sorbed fraction increased during the first 15 days, remained stable or decreased up to 77 days and increased afterwards (five soils); (3) where the sorption took place in 15 first days and no changes were found thereafter (six soils); (4) where almost all added selenate was first sorbed by 77 days, but half of it was soluble again at 161 days (two soils). During the first 2 weeks after the addition of selenate into the soils, chemical factors seemed to be the most important factors determining the selenium retention; later on, however, soil microbiological activity appeared to determine the fate of the sorped fraction.