The degradation of tetrachloromethane (carbon tetrachloride-CT) by modified Fenton's reagent (catalyzed hydrogen peroxide) was investigated using a range of hydrogen peroxide concentrations and 1 mM iron(HI) catalyst. The documented reactive species in modified Fenton's reactions, hydroxyl radical (OH.), is not reactive with CT, yet CT degradation was observed in the Fenton's reactions and was confirtned by chloride generation. Because CT is not reactive with OH., a reductive mechanism which may involve superoxide radical anion is proposed for CT degradation in modified Fenton's systems. Scavenging of reductants by excess chloroform prevented CT degradation, confirming a reductive mechanism, Similar to CT, three other oxidized aliphatic compounds, hexachloroethane, bromotrichloromethane, and tetranitromethane, were also degraded by modified Fenton's reagent. The results show that modified Fenton's reactions act through a reductive mechanism to degrade compounds that are not reactive with OH*, which broadens the scope of this process for hazardous waste treatment and remediation. (C) 2002 Elsevier Science B.V. All rights reserved.