Quinone moieties in humic substances have previously been shown to serve as extracellular electron acceptors in different metabolic pathways. Here we show that the humic acid analogue antraquinone-2,6-disulfonate (AQDS) can also serve as an electron donor in the microbial reductive dechlorination of ICE to cis-DCE. In a bioelectrochemical system (BES). equipped with a glassy carbon electrode (cathode) polarized at -250 mV vs. SHE, electrically reduced AQDS served as the shuttle of electrons between the electrode surface and the dechlorinating bacteria. Interestingly, AQDS selectively stimulated only the first step of the TCE dechlorination sequence, leading to the formation of cis-DCE. Bioelectrochemical experiments carried out using a dechlorinating culture, highly enriched in the cis-DCE dechlorinating microorganism Delialococcoides spp., confirmed the inability of reduced AQDS to serve as an electron donor for cis-DCE dechlorination. The results of this study have implications for the development of bioelectrochemical systems for groundwater remediation, as well as for the biogeochemical fate of chlorinated solvents in humic substances-rich subsurface environments. (C) 2010 Elsevier Ltd. All rights reserved.