Ionizing radiation induced degradation of tetrachlorobiphenyl in transformer oil

Complete degradation of 2,2',6,6'-tetrachlorobiphenyl (PCB-54) in transformer oil is achieved by ionizing radiation without degradation of the oil. gamma-Irradiation of transformer oil containing PCB-54 (0.27 mg/g) with a dose of 200 kGy results in complete (>99%) destruction of the PCB. Analysis of samples irradiated with various doses demonstrated gradual degradation of PCB-54 and successive formation and degradation of trichloro-, dichloro-, and monochlorobiphenyl. The final products are mainly biphenyl and inorganic chloride. The mechanism of reductive degradation is studied by pulse radiolysis. The oil contains many aromatic hydrocarbons; the most abundant being biphenyl, fluorene, and phenanthrene. Solvated electrons formed by irradiation of the oil react either with the PCB to lead to dechlorination or with the aromatic hydrocarbons present in the oil to form radical anions. These species are shown to transfer an electron to chlorinated biphenyls relatively rapidly, leading to dechlorination. The rate constants for several su ch reactions, determined in 2-propanol solutions, are in the range of 10(7)-10(8) L mol(-1) s(-1). These rapid reactions explain why PCB can be dechlorinated in oil despite the presence of aromatic hydrocarbons in the oil and despite the formation of biphenyl as a radiolysis product that reacts rapidly with solvated electrons.