DECHLORINATION OF CHLOROBENZENES IN ANAEROBIC ESTUARINE SEDIMENT

The reductive dechlorination of chlorobenzenes (CBs) in an anaerobic e stuarine sediment was examined. The sediment was preexposed to various anthropogenic chemicals from the surrounding industries. The sulfate content (20 mmoles/l) in the interstitial waters indicated that the se diment was sulfidogenic. All the CBs were transformed following a firs t-order reaction kinetics with rate constants ranging from 0.0016 to 0 .0389 day(-1) or half-lives between 17 and 433 days. Disappearance of CBs in autoclaved sediment were observed but to a much less extent tha n in the test sediment. Detected intermediates indicated that the remo val of chlorine atom occurred at all possible positions on the aromati c ring. The contribution of different dechlorination pathways were est imated using branched chain first-order irreversible reaction kinetics . The results showed that the preferential dechlorination was in the f ollowing order: two chlorine atoms on both sides > one of the adjacent chlorine atoms > chlorine with no adjacent chlorine atoms. The major pathway observed for CBs followed a thermodynamically most favorable s tep that gave the highest energy for dechlorination. Copyright (C) 199 6 IAWQ.