Degradation of polychlorinated biphenyls by UV-catalyzed photolysis

Photolysis of five polychlorinated biphenyl (PCB) congeners [2,4,4'-trichlorobiphenyl (PGB 28), 2,2',5,'5-tetrachlorobiphenyl (PGB 52), 2,2',4,5,5'-pentachlorobiphenyl (PGB 101), 2,2',4,4',5,'5-hexachlorobiphenyl (PCB 153) and 2,2',3,4,4',5,'5-heptachlorobiphenyl (PGB 180)] individually and in combination were carried out in the solvents, methanol, ethanol, and 2-propanol. The disappearance of parent congener generally increased with UV intensity. The solvents had significant or limited effect on the removal of PCBs depending oil the congener used. Because 2-propanol was highly toxic and methoxylated products were formed when Methanol was used, ethanol was selected as the optimum solvent. The results Of photolysis Of the PGB mixture showed that PGB 52 was formed and accumulated after 4 h of photolysis. The addition of sodium hydroxide increased the rate of photolysis of the PGB mixture. One hundred percent removal can be obtained of the PGB in mixture in 90 min under optimized conditions. Gas chromatography-mass spectrometry was used to determine the intermediates of the photolysis of PGBS under optimized conditions. For the PGB congeners and mixture studied, the major photolytic intermediates were less chlorinated congeners, and biphenyl was the major product. with minor amounts of hydroxylated PGBs, ethylated, dimethylated, and methylated biphenyls. Biphenyl could be further degraded by a prolonged photolysis. Toxicity of the PGB mixture during photolysis was monitored by the Microtox(R) test. It was found that the toxicity increased at the early stage of photolysis, and gradually decreased as the reaction proceeded. After 90 min, the EC50 of the reaction mixture was similar to that of the Untreated sample.