A method for treating a perfluorocompound-containing gas stream, for example an effluent fluid stream from a semiconductor manufacturing process tool. In one embodiment, a plasma torch is used to generate a plasma from an ionisable gas, such as nitrogen or argon. This plasma is injected into a reaction chamber, which receives both a stream of water vapour and an effluent fluid stream. The ionised stream dissociates the water vapour into heated H+ and OH- ions for reaction with the perfluorocompound. An apparatus for treating a perfluorocompound containing gas stream comprises a means for generating a plasma from a source gas, a means for injecting the plasma into the reaction chamber, a means for conveying the gas stream to the reaction chamber, and a means for conveying a source of H+ and OH- ions to the plasma.