Co-metabolism and adaptation

Highly chlorinated PCBs and pesticides (e.g., mirex and DDT) may be dechlorinated anaerobically by functioning as an electron acceptor. DDT is dechlorinated to DDD by many facultative anaerobic microorganisms under anoxic conditions. DDD can be further dechlorinated or degraded aerobically. 

Reaction 1 is mainly due to facultative bacteria grown anaerobically, whereas reaction 2 occurs often in various animals, notably some DDT-resistant flies. Alkali UV light and some metal salts also catalyze dehydrochlorination. 

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