Reactive activated carbon (RAC) impregnated with palladized iron nanoparticles has been developed to treat polychlorinated biphenyls (PCBs). In this study, we evaluated the effects of various reaction environments on the adsorption-mediated dechlorination of 2-chlorobiphenyl (2-CIBP) in the RAC system. The results were discussed in close connection to the implementation issue of the RAC system for the remediation of contaminated sites with PCBs. Adsorption event of 2-CIBP onto RAC limited the overall performance under condition with a 2-CIBP/RAC mass ratio of less than 1.0 x 10(-4) above which dechlorination of 2-CIBP adsorbed to RAC was the reaction rate-determining step. Acidic and basic conditions were harmful to 2-CIBP adsorption and iron stability while neutral pH showed the highest adsorption-promoted dechlorination of 2-CIBP and negligible metal leaching. Coexisting natural organic matter (NOM) slightly inhibited 2-CIBP adsorption onto RAC due to the partial partitioning of 2-CIBP into NOM in the liquid phase while the 2-CIBP absorbed into NOM, which also tended to adsorb onto RAC, was less available for the dechlorination reaction. Common anions slowed down 2-CIBP adsorption but adsorbed 2-CIBP was almost simultaneously dechlorinated. Some exceptions included strong inhibitory effect of carbonate species on 2-CIBP adsorption and severe detrimental effect of sulfite on 2-CIBP dechlorination. Results on treatment of 2-CIBP spiked to actual sediment supernatants implied site-specific reactivity of RAC. Published by Elsevier B.V.