Anaerobic transformation of compounds of technical toxaphene. I. Regiospecific reaction of chlorobornanes with geminal chlorine atoms.

Technical toxaphene (Melipax) and the single compounds of technical toxaphene (CTTs) 2,2,5-endo,6-exo,8,8,9,10-octachlorobornane (B8-806), 2,2,5-endo,6-exo, 8,9,9,10-octachlorobornane (B8-809), 2,2,5,5,8,9,9,10,10-nonachlorobornane (B9-1025), 2-endo,3-exo,5-endo,6-exo,8,8,9,10,10-nonochlorobornane (B9-1679), 2-endo,3-exo,5-endo,6-exo,8,9,10,10-octachlorobornane (B8-1414), 2-endo,3-exo,5-endo,6-exo,8,8,9,10-octachlorobornane (B8-1412), and 2-exo,3-endo,5-exo,9,9,10,10-heptachlorobornane (B7-1453) were treated with suspensions of the anaerobic bacterium Dehalospirillum multivorans. After 7 d, more than 50% of technical toxaphene was transformed, and the relative amount of early eluting CTTs increased. After 16 d, only 2-exo,3-endo,6-exo, 8,9,10-hexachlorobornane (B6-923), 2-endo,3-exo,5-endo,6-exo, 8,9,10-heptachlorobornane (B7-1001), and a few minor penta- and hexachloro-CTTs were detected in the samples. The result of the transformation was comparable with observations in naturally contaminated sediments and soil. However, the performance with D. multivorans was more simple and reproducible, as well as faster, than use of soil, sediment, or anaerobic sewage sludge. In agreement with reports in the literature, reductive dechlorination at geminal chlorine atoms (gem-C1s) was found to be the major CTT transformation pathway. Experiments conducted with CTTs and gem-C1s at both primary and secondary carbons clarified that the initial C1 --> H substitution takes place at the secondary carbon C2. Furthermore, the 2-endo-C1 position was preferably substituted with hydrogen. In the case of B8-806, the dechlorination at the secondary carbon C2 was approximately 20-fold faster than the subsequent, slow reduction at the primary carbon C8. The three different formerly unknown heptachloro-CTTs, 2-exo,3-endo,6-exo,8,9,9,10-heptachlorobornane (B7-1473), 2-exo, 3-endo,6-endo,8,9,9,10-hepatchlorobornane (B7-1461), and 2-exo, 3-endo,6-exo,8,8,9,10-heptachlorobornane (B7-1470) were found as intermediates of the B8-806/809 transformation. Treatment of B9-1679 with D. multivorans indicated that gem-C1s on the bridge (C8 and C9) are dechlorinated faster than gem-C1s on the bridgehead (C10).