Recalcitrance of DDE (2,2‐BIS‐(4‐chlorophenyl)‐1,1 dichloroethylene) and DPE (1,1‐diphenylethylene) to cometabolic aerobic biodegradation

Abstract

Bacterial degradation of the persistent DDT [1,1,1‐trichloro‐2,2‐bis(4‐chloro‐pheny‐l)ethane] metabolite DDE has not previously been reported. Bacteria from DDT, PCP and PAH contaminated soils and sediments were extracted and evaluated for their ability to degrade DDE and its dehalogenated derivative DPE. Aerobic aromatic hydrocarbon degrading bacteria were enriched using chemostat techniques under both carbon limited and nitrogen limited selection conditions. DDE, ethylbenzene (EB), DPE and dipyridyl ketone oxime (DPKO) were added as structurally related potentially biodegradable carbon and nitrogen sources. No significant degradation of DDE and DPE was observed under these conditions. Pure cultures isolated from the enrichments on nonselective growth media were able to utilise EB and DPKO as carbon and nitrogen sources, respectively but were unable to degrade DDE or DPE alone or in the presence of EB and DPKO. The absence of DDE degradation capacity in the microbial community was confirmed by adding 14C‐DDE to operating chemostats. Labelled volatile degradation products and 14CO2 were not detected. In addition, no products of 14C‐DDE degradation were detected in aqueous or solvent extracts of the reactor contents. The inability to enrich DDE and DPE degrading bacteria may explain DDE persistence in DDT contaminated soils.