Anaerobic biodegradation of DDT residues (DDT, DDD, and DDE) in estuarine sediment

The potential for anaerobic biodegradation of 1,1,1-trichloro-2,2-bischloro-phenylethane (DDT), 1,1-dichloro-2,2,-bischlorophenylethane (DDD), and dichlorodiphenylchloroethylene (DDE) in anoxic sediment slurries collected from the Keelung River was investigated in this study. o,p '- and p,p ' -DDT were dechlorinated to o,p '- and p,p ' -DDD, respectively, and then transformed to other compound(s). 1-Chloro-2,2-bis (p-chlorophenyl) ethylene (DDMU) and trace amount of dichlorobenzophenone (DBP) were detected in sediment slurries amended with p,p ' -DDT or p,p ' -DDD. DDMU was also detected in sediment slurries amended with p,p ' -DDE. The relative transformation rates for both o,p '- and p,p ' -isomers of DDT, DDD, and DDE were DDT > DDD > DDE. Re-addition of DDT, DDD, or DDE to the sediment slurries after initial removal enhanced the respective dechlorination rates. The transformation rates of the p,p ' -isomers of both DDT and DDD were faster than those of the respective o,p ' -isomers. p,p ' -DDT dechlorination in the p,p ' -DDT-adapted sediment slurries were inhibited by the addition of molybdate, or molybdate plus sulfate, but not inhibited by the addition of sulfate. Addition of bromoethane-sulfonic acid (BESA) slightly inhibited p,p ' -DDT dechlorination. Non-adapted sediment slurries lost the ability to dechlorinate pentachlorophenol during adaptation to p,p ' -DDT. p,p ' -DDD was the major transformation product of p, p ' -DDT in 3,4,4 ' ,5-tetrachlorobiphenyl-adapted sediment slurries, which suggested that the microbial community in the 3,3,4 ' ,5-CB-adapted sediment was unable to remove chlorine from the aromatic rings of p,p ' -DDT.