Fate of 3, 3,'-dichlorobenzidine in surface water systems

摘要

Release of 3, 3'-dichlorobenzidine (DCB), an intermediate in dye manufacturing and its two congeners, monochlorobenzidine and benzidine, are of environmental concern due to their carcinogenic nature. Laboratory experiments have been conducted to elucidate the fate of these compounds in sediment-water systems. The sediments from Lake Macatawa (MI) were vaiable in composition, ranging from sandy sediments with 1 to 2.6 percent organic carbon to silty-clay sediments with 7.5 to 18.2 percent organic carbon. Bottles containing sediment/water mixtures were spiked with DCB and incubsted at 20 deg C for eight months under anaerobic conditions. Autoclaved sediment samples in distilled water were also spiked with DCB and incubated for use as a control. Organic carbon contents and particle size analyses were performed on each type of sediment. Sorption isotherms were evaluated for DCB and benzidine to determine the sorption pattern for these different sediment types; lake water was used in the sorption experiments to mimic the original environment. Dehalogenation of 3,3'-dichlorobenzidine was observed over the course of these experiments. Autoclaved samples did not show any degradation of 3, 3'-dichlorobenzidine. Product studies revealed that benzidine was released into the sediment and water as a result os DCB dehalogenation, which was mediated by anaerobic microbial activity. Preliminary evidence of the existence of an unstable intermediate, monochlorobenzidine, was also observed. The shift in partitioning behavior between DCB and benzidine resulted in release of benzidine to the aqueous phase.