3,3'-DICHLOROBENZIDINE TRANSFORMATION PROCESSES IN NATURAL SEDIMENTS

Release of 3,3'-dichlorobenzidine (DCB), an intermediate in dye manufa cturing, and its congeners are of environmental concern due to their c arcinogenic nature. To elucidate the fate of these compounds in sedime nt/water systems, sediment/water mixtures were spiked with DCB and inc ubated at 20 degrees C for 12 months under anaerobic conditions. The s ediments used in this study were collected from Lake Macatawa (Holland , MI) and ranged in composition from silty-clay to sandy. Dehalogenati on of DCB to benzidine appeared to take place through a transient inte rmediate, 3-monochlorobenzidine, which was observed in timecourse anal yses of the sediment/water mixtures. No metabolites were observed in a utoclaved samples, suggesting that dehalogenation of DCB in anaerobic sediment/water systems was mediated by microbial activity. The product of dehalogenation (benzidine) is more toxic to humans than the parent compound, DCB. From sediment/water distribution experiments, DCB show ed greater affinity for the sediment phase than its non-chlorinated de rivative, benzidine. Therefore, progressive dehalogenation of DCB in a naerobic lake sediments is expected to yield a greater total concentra tion of aromatic amines in the solution phase, a shift to a more toxic form, and greater potential for transport in the environment.