Bacterial degradation of a mixture obtained through the chemical modification of polychlorinated biphenyls by polyethylene glycols

Abstract

Polychlorinated biphenyls (PCBs), also known by the trade name Sovol, are toxic industrial wastes. They have been subjected to chemical treatment by polyethylene glycols (PEGs) and potassium hydroxide. As a result of the interaction of the Sovol with various molecular mass PEGs (MMPEG-4 ∼ 200, MMPEG-22 ∼ 1000), water-soluble mixtures M1 and M2 containing mono(polyethylene glycol)oxy-derivatives (PCB-PEG-4 and PCB-PEG-22), polychlorobiphenylols, and unreacted PCB congeners (PCB 44, PCB 47, PCB 49, PCB 52, and PCB 66) were obtained. It was shown for the first time that mixtures M1 and M2 are susceptible to bacterial degradation without their fractionation. According to the gas-liquid chromatography with flame-ionization and mass-spectrometric detection, the Rhodococcus wratislaviensis KT112-7 strain degraded all of the chemical compounds occurring in the mixtures. In a 5-day experiment, it was found that the KT112-7 strain decomposes mono(polyethylene glycol)oxy-derivatives completely (by 100%) and polychlorobiphenylols and PCB congeners by 90–95% in the M1 and M2 mixtures. The culture medium did not contain transformation products, whereas free chlorine ions were accumulated (72–94% of the maximum possible amount). Thus, the use of the chemical modification and consecutive bacterial degradation provided an effective destruction of technical PCB mixtures with a high content of highly chlorinated congeners.