2,6-dibromobiphenyl primes extensive dechlorination of Aroclor 1260 in contaminated sediment at 8-30°C by stimulating growth of PCB-dehalogenating microorganisms

We applied the most probable number (MPN) method to test the hypothesis that 2,6-dibromobiphenyl (26-BE) primes polychlorinated biphenyl (PCB) dechlorination by stimulating the growth of microorganisms that dehalogenate 26-BE and PCBs. The experiments were conducted in anaerobic microcosms of Aroclor 1260-contaminated sediment from Woods Pond (Lenox, MA). We estimate that the number of microorganisms capable of dehalogenating 26-BE and PCBs increased approximately 1000-fold (from 3-4.9 x 10(5) to 2-5.8 x 10(8) cells/g of sediment [dry weight] or from 0.7-1.2 x 10(5) to 0.5-1.4 x 10(8) cells/mL of wet sediment) after priming for 48 days with 26-BB (1050 mu mol/L of slurry) in the presence of 10 mM malate at 22 degrees C. All MPN samples that showed debromination of 26-BE also dehalogenated Aroclor 1260 even in the high dilutions. These results demonstrate for the first time that halogenated biphenyls prime PCB dechlorination by stimulating the growth of PCB-dechlorinating microorganisms. 26-BE primed exclusively meta-dechlorination of the PCBs (Process N), which effected extensive decreases (75-88%) in the hexa-through nonachlorobiphenyls in only 5-8 months at temperatures as low as 8 degrees C. The highest observed rates of primed dechlorination of Aroclor 1260 ranged from similar to 250 to similar to 1150 pmol of CI mL(-1) day(-1) at 8 and 25 degrees C, respectively.