Microbial dechlorination of three PCB congeners in river sediment

We investigated the potential for the anaerobic degradation of three PCB co ngeners (2,3,5,6-CB, 2,3,4,5-CB, and 2,3,4,5,6-CB) in sediments collected f rom five monitoring sites along the Keelung River in northern Taiwan. Optim al conditions for congener dechlorination were 30 degreesC and pH 7.0. Inte r-mediate 2,3,4,5-CB products were identified as 2,3,5-CB, 2,4,5-CB, and 2, 5-CB. Intermediate 2,3,4,5,6-CB products were identified as 2,3,5,6-CB, 2,3 ,6-CB, and 2,5-CB. For 2,3,5,6-CB, intermediate products were identified as 2,3,6-CB and 2,5-CB. Dechlorination rates for PCB congeners were observed as (fastest to slowest): 2,3,4-CB > 2,3,4,5-CB > 2,3,4,5, 6-CB > 2,3,5, 6-C B > 2,2', 3, 3' 4, 4'-CB > 2,2',4,4',6,6'-CB > 2,2',3,4,4',5,5'-CB > 2,2',3 ,3',4,4',5,5'-CB. Rates decreased for mixtures of the eight congeners. Dech lorination rates for the three primary congeners under different reducing c onditions occurred in the order of (fastest to slowest): methanogenic condi tion > sulfate-reducing condition > nitrate-reducing condition. Under metha nogenic and sulfate-reducing conditions, dechlorination rates were enhanced by the addition of lactate, pyruvate, or acetate, but delayed by the addit ion of manganese oxide, or ferric chloride. Under nitrate-reducing conditio n, dechlorination rates were delayed by the addition of lactate, pyruvate, acetate, manganese oxide or ferric chloride. Treatment with such microbial inhibitors as bromoethanesulfonic acid (BESA) or molybdate revealed that me thanogen and sulfate-reducing bacteria were involved in the dechlorination of these three PCB congeners. (C) 2001 Published by Elsevier Science Ltd.