An incubation experiment was conducted to investigate the microbial biomass associated Cu in fourrrrrrrrrrncontrasting soils to which an alkaline stabilised sewage sludge cake was applied. The organisms of sludge-rrrrrrrrrnamended and control soils were killed using ry-irradiation technique, and the aqueous and acid-extractable Currrrrrrrrnconcentrations were determined. Addition of the sludge product increased significantly the concentration ofrrrrrrrrrnboth the aqueous and dilute HOAc-extractable Cu in all the irradiated soils compared to the non-sterilisedrrrrrrrrrnsludge/soil mixtures, but the increase was more pronounced in the dilute acid-extractable Cu, indicating thatrrrrrrrrrnthe Cu rendered extractable in water and dilute acetic acid by 7-irradiation existed in the both soil liquidrrrrrrrrrnand solid phases. The additional increase in extractable Cu following the biocidal treatment is likely to berrrrrrrrrndue to release of Cu from the same fraction of soil microbial biomass. An incubation experiment was conducted to investigate the microbial biomass associated Cu in four r r r r r r r rcontrasting soils to which an alkaline stabilized sewage sludge cake was applied. The organisms of sludge - r r r r r r r r namended and control soils were killed using ry-irradiation technique, and the aqueous and acid-extractable Cu r r r r r r r r r nconcentrations were determined. Addition of the sludge product increased significantly the concentration of r r r r r r r r nboth the aqueous and dilute HOAc-extractable Cu in all the irradiated soils compared to the non-sterilised r r r r r r r r r r rludge / soil mixtures, but the increase was more pronounced in the dilute acid-extractable Cu, indicating that r r r r r r r r nthe Cuinated extractable in water and dilute acetic acid by 7-irradiation existed in the both soil liquid r r r r The additional increase in extractable Cu following the biocidal treatment is likely to be r r r r r r r r r ndue to release of Cu from the same fraction of soil microbial biomass.