BACKGROUND: Tetrachloroethylene (PCE) and hexachloroethane (HCA) degradation, individually and in mixture, is investigated by Fe(III) or Fe(III)-citrate initiated Fenton reaction under a range of hydrogen peroxide (H2O2) concentrations to illustrate the applicability and constraints of Fenton chemistry in degrading contaminants in polluted groundwater. RESULTS: In individual solutions Fe(III) rapidly degraded PCE for all H2O2 concentrations, but HCA at = 0.2 mol L-1 H2O2; the apparent PCE degradation rate initially increased but then decreased with increasing H2O2, while the HCA degradation rate was either unaffected or increased. With Fe(III)-citrate PCE degradation was lower and no HCA degradation occurred. PCE degradation was lower in PCE-HCA mixture, but the trend with H2O2 concentration was similar to the individual chemical; for HCA the residual was smaller for higher H2O2 concentration, but the apparent degradation rate constant was unaffected. CONCLUSION: Fe(III) catalyzed reactions can potentially degrade chemicals through reductive as well as oxidative transformations. Degradation of chemicals in mixtures occurs at a slower rate due to competition for radical moieties. The Fe(III)-citrate complex further slowed chemical transformation. This study expands on the use of different forms of iron to catalyze the Fenton reaction to degrade chemicals. Copyright (C) 2012 Society of Chemical Industry