This study investigated the rates and pathways of gamma-hexachlorocyclohexane (gamma-HCH) dechlorination by granular zero-valent iron under different pH, iron dosage and temperature conditions. It was found that gamma-HCH was rapidly reduced to benzene and chlorobenzene (CB) with benzene as the major product and that the dechlorination likely follows three steps of dichloroelimination to benzene, or two steps of dichloroelinninations and one step of dehydrohalogenation to CB. The calculated pseudo-first-order rate of gamma-HCH degradation was 0.0125 min(-1) at pH 6.73,25 degrees C and 10 g L-1 iron dosage, corresponding to 55.5 min of half-life. It was also found that the rate of gamma-HCH dechlorination increases as a function of reaction temperature and zero-valent iron dosage and decreases as a function of solution pH. The calculated activation energy is 33.5 kJ mol(-1) at pH 6.73, which is much lower than that of dehydrohalogenation facilitated by hydroxyl under basic conditions. The study suggested that zero-valent iron could be used to effectively and efficiently transform gamma-HCH. (C) 2008 Elsevier B.V. All rights reserved.