[en] OH-radical-induced dechlorination of pentachlorophenol (PCP) has been studies pulse and γ-radiolytically. OH radicals react with PCP by both electron transfer (53%) and addition followed by very rapid HCl-elimination to form phenoxyl radicals. The phenoxyl radicals decay to form products (e.g. chloranil) that unstable in alkaline aqueous solution and release some more Cl^-, therefore G(Cl^-) is high. Primary HPLC-MS analysis reveals that some quinones among the final products, whose toxicity remains unclear. Ozone can also oxidize PCP very rapidly, and this oxidation may destroy the benzene ring of PCP