Reductive transformations of halogenated aromatic hydrocarbons in anaerobic water-sediment systems: Kinetics, mechanisms and products

Abstract

Abstract The degradation of several classes of halogenated aromatic hydrocarbons in methanogenic sediment-water systems was examined in laboratory studies. Several transformation processes were shown to occur, leading to formation of a variety of products. In the study a clear distinction could be made between transformation processes taking place immediately upon incubation of the compounds and processes taking place after a characteristic period of varying length. γ-Irradiation was used to quench biological reactions and thus assess the impact of those processes on the overall rates of degradation of the studied compounds. The kinetics of both the initial and the final processes were pseudo-first-order, with half-lives ranging from <0.46 d to no detectable degradation for a number of multiply halogenated benzenes. Compounds were selected with the aim of obtaining a maximum variation in chemical reactivity and physical properties. The sediments were selected with the aim of assessing several environmental factors influencing the kinetics of reduction.