Temperature determines the pattern of anaerobic microbial dechlorination of Aroclor 1260 primed by 2,3,4,6-tetrachlorobiphenyl in Woods Pond sediment

Abstract

Reductive dechlorination of the Aroclor 1260 residue in Woods Pond (Lenox, Mass.) sediment samples was investigated for a year at incubation temperatures from 4 to 66°C. Sediment slurries were incubated anaerobically with and without 2,3,4,6-tetrachlorobiphenyl (2346-CB; 350 μM) as a primer for dechlorination of the Aroclor 1260 residue. Dechlorination of the Aroclor residue occurred only in live samples primed with 2346-CB and only at 8 to 34°C and 50 to 60°C. The extent and pattern of polychlorinated biphenyl (PCB) dechlorination were temperature dependent. At 8 to 34°C, the dechlorination resulted in 28 to 65% decreases of the hexa- through nonachlorobiphenyls and corresponding increases in the tri- and tetrachlorobiphenyls. At 12 to 30°C, 30 to 40% of the hexa- through nonachlorobiphenyls were dechlorinated in just 3 months. The optimal temperature for overall chlorine removal was 20 to 27°C. We observed four different microbial dechlorination processes with different but partially overlapping temperature ranges, i.e., Process N (flanked meta dechlorination) at 8 to 30°C, Process P (flanked para dechlorination) at 12 to 34°C, Process LP (unflanked para dechlorination) at 18 to 30°C, and Process T (a very restricted meta dechlorination of specific hepta- and octachlorobiphenyls) at 50 to 60°C. These temperature ranges should aid in the development of strategies for the enrichment and isolation of the microorganisms responsible for each dechlorination process. The incubation temperature determined the relative dominance of the four PCB dechlorination processes and the extent and products of dechlorination. Hence, understanding the effects of temperature on PCB dechlorination at contaminated sites should assist in predicting the environmental fate of PCBs or planning bioremediation strategies at those sites.