The biotransformation of atrazine added to a mixture of cotton and wheat straw (CWS) and inoculated with the white-rot fungus, Pleurotus pulmonarius, was studied, as a proposed system for bioremediation. The concentration of methanol-extractable atrazine was reduced, due to both biological transformation and physical-chemical adsorption to the straw. Only 32% of the total radioactivity added as C-14-ring-labeled atrazine to pasteurized CWS inoculated with Pleurotus was extracted two weeks after fungal colonization, and less than 70% from non-inoculated CWS. The reduction in extractable radioactivity increased with time of incubation. No mineralization of the triazine ring was found during six weeks of incubation, but transformation to two groups of atrazine metabolites, chlorinated and dechlorinated, occurred as a result of the activity of the fungus inoculated and natural bacterial population. Unextractable radioactivity was recovered after digesting the colonized substrate with H2SO4, indicating adsorption of the herbicide and its metabolites to the straw. The results suggest that this process can be used to detoxify atrazine by both adsorption and biodegradation. Copyright (C) 1996 Elsevier Science Ltd.