Plumes of contaminated groundwater often pass through an oxic/anoxic interface when they discharge into surface water bodies. We tested the hypothesis that contaminants recalcitrant under anaerobic conditions but degradable under aerobic conditions can be biodegraded at the interface resulting in the protection of the overlying water. Flow-through columns containing sediment and water were used to evaluate degradation of synthetic organic compounds at the thin organic layer at the sediment/water interface. Sediment samples collected from several sites contaminated with nitrobenzene (NB) or chlorobenzene (CB) were tested for their biodegradation capacities in the columns. The biodegradation capacities of sediment in the columns were 2-4,2 g CB.m(-2).d(-1) and 6.5 g NB.m(2).d(-1). Bacteria able to carry out rapid and complete biodegradation of CB or NB were detected in the sediments prior to the experiments, which suggested the presence of an active microbial community at the contaminated sites. The results revealed robust biodegradation of toxic compounds migrating across the sediment/water interface and indicate that the biodegradation capacities were sufficient to eliminate transport of the contaminants to the overlying water in the field.