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Enhanced Biodegradation of Polychlorinated Biphenyls in Soil by Analog Enrichment and Bacterial Inoculation¹

ABSTRACT

Carbon-14-labeled polychlorinated biphenyls (PBC) representing the commercial Aroclor 1242 mixture (a mixture of chlorinated biphenyls) were incubated in soil over a 210-d period to determine if biodegradation could be enhanced by additions of straw and sludge, aerobic and anaerobic incubations, or combinations thereof. Although PCB (100 mg/kg) had no effect on microbial respiratory processes in soil, mineralization did not exceed 3% of the total added. Also, neither ¹⁴CO₂ nor ¹⁴CH₄ was produced from anaerobic incubations, although both gases were produced from organic matter additions. Further experimentation was undertaken to investigate the possibility that the soil lacked either an indigenous microflora capable of metabolizing PCB or a suitable substrate analog which promoted their activity or growth. Inoculation with Acinetobacter P6 (Furukawa) alone did not enhance mineralization of ¹⁴C-PCB. However, when enriched with substrate analog biphenyl, 20 to 27% of the label was recovered as ¹⁴CO₂ over a 63-d period compared to < 1% ¹⁴CO₂ for the unenriched controls. Uninoculated and enriched treatments also greatly enhanced mineralization yielding 15 to 20% as ¹⁴CO₂, yet the extent of primary degradation of PCB (i.e., disappearance) was greater when both Acinetobacter and biphenyl were added. Analog enrichment with biphenyl is the most important factor effecting PCB degradation in soil, but additional enhancement is brought about by inoculation with Acinetobacter, which is superior to the indigenous microflora with respect to diversity towards metabolism of the isomers present in Aroclor 1242.

Key Words: xenobiotics • organochlorines • Acinetobacter • Aroclor • chlorinated hydrocarbons

¹ Contribution from the Dep. of Soil & Environmental Sciences, Univ. of California, Riverside, CA 92521.

² Postdoctoral associate, staff research associate, and professor, respectively, Univ. of California, Riverside. Present address of senior author is Swiss Federal Inst. of Forestry Research, Birmensdorf, Switzerland.

Received for publication February 19, 1984.

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