Low-Temperature Microbial Aerobic Degradation of Polychlorinated Biphenyls in Sediment

To test for low-temperature microbial aerobic PCB degradation, water-saturated samples of PCB-contaminated upper Hudson River sediment spiked with Aroclor 1242 were incubated at 4 °C for several months. Principal components analysis of the PCBs, quantified by GC−ECD and GC−MS, indicated the loss of specific congeners within the top 15 mm of sediment. In contrast, no loss of PCBs was observed in the deeper region (>15 mm from the surface) of the sediment or in any region of similarly treated sediment samples that were autoclaved prior to Aroclor 1242 addition. Loss of specific di- and trichlorobiphenyls typical of microbial aerobic degradation was first indicated at 1.4 months, and >50% loss had occurred by 5 months. Initially, the sediment was dark brown. However, by 2 months a lighter, rust-colored layer developed at the top 6 mm that increased to ∼10 mm by 5 months and to ∼15 mm by 10 months. The color change, due at least in part to formation of hydroxylamine-reducible ferric oxide, indicated the depth to which oxygen was available and the depth to which PCB degradation occurred. In addition, chlorobenzoic acid metabolites of microbial aerobic PCB degradation were detected in the rust-colored layer. These observations demonstrate that low-temperature microbial aerobic PCB degradation can occur in PCB-contaminated sediment.