A method for the decomposition of halogenated organic compounds contained in a contaminated medium comprises adding an alkali metal carbonate or bicarbonate to the contaminated medium in an aqueous solution or in a solvent having a boiling point of at least 200.degree. C., or in the form of a solid dispersion or suspension. The medium is heated to dehydrate the medium and then is further heated at a temperature between about 250.degree. and 400.degree. C. to effect decomposition of the halogenated organic compounds. An acid is then added to the medium in an amount sufficient to neutralize the same.