Biodegradation of 3,3′-dichlorobenzidine in freshwater lake sediments

3,3′-Dichlorobenzidine (DCB) and its degradation products, 3-chlorobenzidine (MCB) and benzidine, are of environmental concern due to their toxic and carcinogenic nature. Laboratory experiments have been conducted to elucidate the biodegradation behavior of DCB in Lake Macatawa (Holland, Michigan) sediment–water systems at 4, 24, and 30 °C incubation temperatures. Sediment samples varied in pH (6.45–7.41), total organic carbon (OC) content (1.4–17.1), and particle size distribution (silty-clay to sandy). Biodegradation of DCB was observed in non-autoclaved samples that were incubated at 4, 24, and 30 °C for approximately 12 months. The dechlorination rate as a function of OC content was essentially found constant at 4 °C and 24 °C, but demonstrated a roughly linear increase at 30 °C, thereby suggesting that OC content might be correlated to dechlorination rate at 30 °C incubation temperature. The rate as a function of particle size (e.g., <74 µm) did not demonstrate a clearly defined relationship. Key words: 3,3′-dichlorobenzidine, 3-chlorobenzidine, benzidine, biodegradation.