Influence of incubation temperature on the microbial reductive dechlorination of 2,3,4,6-tetrachlorobiphenyl in two freshwater sediments

We studied the impact of incubation temperatures on the dechlorination of 2,3,4,6-tetrachlorobiphenyl (2346-CB) in two sediments from different climates: polychlorinated biphenyl (PCB)-free sediment from Sandy Creek Nature Center Pond (SCNC) in Athens, Ga., and PCB-contaminated sediment from Woods Pond (WP) in Lenox, Mass, Sediment slurries were incubated anaerobically with 350 mu M 2346-CB for 1 year at temperatures ranging from 4 to 66 degrees C, Most of the 2346-CB was dechlorinated between 12 and 34 degrees C in both sediments and, unexpectedly, between 50 and 60 degrees C in WP sediment, This is the first report of PCB dechlorination al thermobiotic temperatures. The data reveal profound differences in dechlorination rate, extent, and products as a function of sediment and temperature. The highest observed rate of dechlorination of 2346-CB to trichlorobiphenyls occurred at 30 degrees C in both sediments, but the rate was higher for WP than for SCNC sediment (46 versus 16 mu mol liter(-1) day(-1)). For SCNC sediment the rate of dechlorination dropped sharply below 30 degrees C, but for WP sediments it was near optimal from 20 to 34 degrees C and then dropped sharply below 20 degrees C. In WP sediment most of the meta chlorines were removed between 8 and 34 degrees C and between 50 and 60 degrees C, para dechlorination was restricted from 18 to 34 degrees C and was optimal at 20 degrees C. ortho dechlorination occurred between 8 and 30 degrees C, with optima around 15 and 27 degrees C, but the extent was highly variable. In SCNC sediment complete meta dechlorination occurred from 12 to 34 degrees C and para dechlorination occurred from 18 to 30 degrees C; both were optimal at 30 degrees C, No ortho dechlorination was observed, Dechlorination products were 246-CB, 236-CB, and 26-CB (both sediments) and 24-CB, 2-CB, and 4-CB (WP sediment), The data suggest that in SCNC sediment similar factors controlled meta and para PCB dechlorination over a broad temperature range (18 to 30 degrees C) but that in WP sediment there were multiple temperature-dependent changes in the factors controlling ortho, meta, and para dechlorination, We attribute the differences observed in the two sediments to differences in their PCB-dechlorinating communities.