Effect of incubation temperature on the route of microbial reductive dechlorination of 2,3,4,6-tetrachlorobiphenyl in polychlorinated biphenyl (PCB)-contaminated and PCB-free freshwater sediments

Abstract

We studied the influence of temperature (4 to 66°C) on the microbial dechlorination of 2,3,4,6-tetrachloro-biphenyl (2,3,4,6-CB) incubated for 1 year in anaerobic sediments from Woods Pond in Lenox, Mass., and Sandy Creek Nature Center Pond (SCNC) in Athens, Ga. Seven discrete dechlorination reactions were observed, four of which occurred in both sediments. These were 2,3,4,6-CB → 2,4,6-CB, 2,3,4,6-CB → 2,3,6-CB, 2,4,6-CB → 2,6-CB, and 2,3,6-CB → 2,6-CB. Three additional reactions occurred only in Woods Pond sediment. These were 2,4,6-CB → 2,4-CB, 2,4-CB → 2-CB, and 2,4-CB → 4-CB. The dechlorination reactions exhibited at least four different temperature dependencies in SCNC sediment and at least six in Woods Pond sediment. We attribute the discrete dechlorination reactions to different polychlorinated biphenyl (PCB)-dechlorinating microorganisms with distinct specificities. Temperature influenced the timing and the relative predominance of parallel pathways of dechlorination, i.e., meta versus para dechlorination of 2,3,4,6- CB and ortho versus para dechlorination of 2,4,6-CB and 2,4-CB. meta dechlorination of 2,3,4,h-CB to 2,4,6-CB dominated at all tested temperatures except at 18 and 34°C, where para dechlorination to 2,3,6-CB dominated in some replicates. The dechlorination of 2,4,6-CB was restricted to ~15 to 30°C in both sediments. Temperature affected the lag time preceding the deehlorinution of 2,4,6-CB in both sediments and affected the preferred route of its dechlorination in Woods Pond sediment. para dechlorination dominated at 20°C, and ortho dechlorination dominated at 15°C, but at 18 and 22 to 30°C the relative dominance of ortho versus para dechlorination of 2,4,6-CB varied. These data indicate that field temperatures play a significant role in controlling the nature and the extent of the PCB dechlorination that occurs at a given site.