Changes of soil and plant tissue selenium status in an upland grassland contaminated by selenium-rich agricultural drainage sediment after ten years transformed from a wetland habitat

A field survey was conducted in 1989, 1994, and 1999 in order to monitor th e soil and vegetation Se concentrations at the Kesterson upland grassland c ontaminated by Se-rich drainage sediment. The rate of Se dissipation estima ted by the change of soil Se concentration, via volatilization, found to be about 1.1% per year. Soil water-extractable Se increased in 1994, but grea tly reduced in 1999, The increase of soil Se concentration in the top 15 cm of soil at the fresh-soil fill sites indicates that the plants were able t o effectively take up the soluble soil Se from the lower soil profile and t o deposit it on the top of the field. This process may reduce the rate of l eaching of soil Se. Overall, the concentration of soil water-soluble Se was relatively low and it is unlikely that problems of transport of Se from th e Kesterson soil to the adjacent uncontaminated environment by leaching can occur. Plant tissue Se concentration was found to coincide with the soil m ater-extractable Se concentration. The average plant tissue Se concentratio n and soil water-extractable Se detected in 1999 was about 10 mug Se g(-1) and 110 mug Se kg(-1) dry weight, respectively, and the estimated bioaccumu lation value of this upland grassland is less than 10% of the previous wetl and habitat. Therefore, the existing Kesterson grassland should not be at h igh risk to the environment. (C) 2000 Academic Press.