How aerobic and anaerobic microbial activities modify Se aqueous, gaseous and solid distribution in soils

Titre du congrès :9th International Conference on the Biogeochemistry of Trace Elements (9th ICOBTE) Ville du congrès :Pékin Date du congrès :15/07/2007

Many redox transformations of selenium in soils can be mediated by microorganisms, either directly favouring reduction and volatilisation, or indirectly by affecting the chemical properties of the soil solution. The aims of this study were to determine the effects of microbial activities on Se distribution between the gaseous, liquid and solid phases and to distinguish between bacterial and fungal contributions to Se transformations. Aerobic incubations were performed with soil samples, some of which had previously been sterilised and/or amended with glucose. A part of the amended soil samples were treated with either a bactericide or a fungicide. The distribution of selenium was determined by analysing Se-75 in the aqueous, solid and gaseous phases. Abiotic interactions between soil particles and selenite occurred mainly in the first hour of incubation and led to the immobilisation of 50 % of the applied selenium. Bacterial activities increased the amount of selenium retained by the soil up to 95 %. Both bacteria and fungi appeared to contribute to the volatilisation of Se. However, fungi alone produced 8-fold more volatile selenium than bacteria alone. When only bacteria were present, the amount of volatilised selenium was the same as when bacteria and fungi were present.