Rapid anaerobic degradation of toxaphene in sewage sludge

We studied the degradation of technical toxaphene in anaerobic sewage sludg e from a municipal waste water treatment plant. Chlorobornanes, chlorocamph enes and related compounds were rapidly degraded, with degradation rates in the order of decachloro>nonachloro>octochloro>heptachloro approximate to h exachloro compounds. The half-lives of individual congeners ranged from <1 day to several days. We also studied the degradation of technical toxaphene in previously sterilized sludge (control), and found it was slower than in the anaerobic sludge. The chlorobornanes that degraded most rapidly in the non-sterilized anaerobic sludge were those with gem chloro substitution on the 6-member carbon-ring, including the toxic congeners, Toxicant A and B. Non-gent chloro substituted congeners, like the biologically persistent P2 6 and P50, also degraded, but less rapidly. Toxaphene degradation in sewage sludge proceeded primarily via reductive dechlorination, leading to HxSed, HpSed, TC2 and other persistent metabolites. Enantioselective determinatio ns indicated little, if any, enantioselectivity in the formation and/or deg radation of these compounds. The isomer and enantiomer profiles of the hexa -, hepta-, and octachlorobornanes are similar to those observed in sediment from the Baltic Sea, suggesting that technical toxaphene is the source of these compounds and that its composition was changed via similar anaerobic degradation pathways. (C) 2000 Elsevier Science Ltd. All rights reserved.