ABSTRACT
PCB-1254 under ligninolytic (low-N) and under nonligninolytic (high-N) media. Degradation was more extensive in a malt extract media. The maximum percent decrease by weight in total congeners for PCB-1254 was 30.5 %. All congeners were degraded extensively regardless of the number of chlorines at the ortho, meta, and para positions indicating nonspecificity for the position of chlorine atoms (Yadav et al., 1995). Soil. In two California soils (foc = 0.3 and 11.3%), 95% of the applied amount was recovered after 1 yr with no change in the congener composition. In the four remaining soils containing less organic carbon (0.06 to 1.9%), degradation resulted in preferential loss of congeners with the lowest molecular weight (Iwata et al., 1973). Photolytic. PCB-1254 in a 90% acetonitrile/water solution containing 0.2-0.3 M sodium borohydride and irradiated with UV light (λ = 254 nm) reacted to yield dechlorinated biphenyls. After 16 h, no chlorinated biphenyls were detected. Without sodium borohydride, only 25% of PCB-1254 were destroyed after 16 h (Epling et al., 1988). In a similar experiment, PCB-1254 (1,000 mg/L) in an alkaline 2-propanol solution was exposed to UV light (λ = 254 nm). After 30 min, all of the PCB-1254 isomers were converted to biphenyl. When the radiation source was sunlight, only 25% was degraded after a 20-h exposure. But when the sensitizer phenothiazine (5 mM) was added to the solution, photodechlorination of PCB-1254 was complete after 1 h at 350 nm. In addition, when PCB-1254 contaminated soil was heated at about 80 °C in the presence of di-tert-butyl peroxide, complete dechlorination to biphenyl was observed (Hawari et al., 1992). When PCB-1254 in a methanol/water solution (10:3) containing sodium methyl siliconate was irradiated with UV light (λ = 300 nm) for 5 h, most of the congeners dechlorinated to biphenyl (Hawari et al., 1991). In a similar experiment, a dilute solution of PCB-1254 in cyclohexane was exposed to a Montreal sunlight in December and January for 55 d at 10 °C. Dechlorination of the higher chlorinated congeners at the ortho position was observed. In addition, two cyclohexyl adducts of polychlorinated biphenyls containing three and four chlorine atoms were also formed in small amounts (0.6% of the original PCB-1254 added) (Lépine et al., 1992). The photolysis rate decreases as the oxygen content increases (Safe et al., 1976). Chemical/Physical. When PCB-1254-contaminated sand was treated with a poly(ethylene glycol)/potassium hydroxide mixture at room temperature, 81% reacted after 6 d forming aryl poly(ethylene glycols) (Brunelle and Singleton, 1985). Using methanol, ethanol, or 2-propanol in the presence of nickel chloride and sodium borohydride, dechlorination resulted in the formation of biphenyls with smaller quantities of mono-and dichlorobiphenyls (Dennis et al., 1979). Zhang and Wang (1997) studied the reaction of zero-valent iron powder and palladium-coated iron particles with trichloroethylene and PCBs. In the batch scale experiments, 50 µL of 200 µg/mL PCB-1254 in methanol was mixed with 1 mL ethanol/water solution (volume ratio = 1/9) and 0.1 g of wet iron or palladium/iron powder in a 2-mL vial. The vial was placed on a rotary shaker (30 rpm) at room temperature for 17 h. Trichloroethylene was completely dechlorinated by the nanoscale palladium/iron powders within the 17-h time period. Only partial dechlorination of PCB-1254 was observed when wet iron powder was used. When exposed to fire, black soot containing PCBs, polychlorinated dibenzofurans, and chlorinated dibenzo-p-dioxins is formed (NIOSH, 1997). PCB-1254 will not hydrolyze to any reasonable extent (Kollig, 1993). When PCB-1254 was heated up to 315 °C in a closed system, no appreciable decomposition was observed (Monsanto, 1960). Mackay and Wolkoff (1973) estimated an evaporation half-life of 1.2 min from a surface water body that is 25 °C and 1 m deep. Exposure limits: Potential occupational carcinogen. NIOSH REL: TWA 1 µg/m3, IDLH 5 mg/m3; OSHA PEL: TWA 0.5 mg/m3; ACGIH TLV: TWA 1 mg/m3 (adopted).
