Pcbs Photodegradation Of The Anionic Surfactant (sds) Solution

Polychlorinated biphenyls (PCBs) are wildly distributed environmentalcontaminants. Though they are physically and chemical1y stable and generallyrecalcitrant to biodegradation, they are photodegradable. Characteristics andpathways of photodegradation of polychlorinated biphenyls (PCBs) in varioussolutions are reviewed. Dechlorination was attributed to the main pathway forPCB photolysis. In addition, hydroxylation was the minor pathway for PCBphotolysis in polar solvents such as water and alcohols. The photo-reactivity ofPCBs was related to the position and quantity of chlorines on the PCB congeners.The application of photolysis in remediation of PCB contaminated soils is alsobriefly reviewed.Photolysis of 2,2',4,4'-tetrachlorobiphenyl dissolved in anionic surfactant(sodium dodecyl sulfate) micellar solutions was studied. Under UV irradiation at254 nm, 2,2',4,4'-tetrachlorobiphenyl was decomposed. By measuring UV-VISspectra ofphotolyzed samples, it has been found that the K band of spectra shiftedblue as photolysis time increased, which implied a possible stepwisedechlorination with preferential removal of the ortho chlorines. Less chlorinatedPCB congeners (2,4,4'-trichlorobiphenyl, 4,4'-dichlorobiphenyl, 4-chlorobiphenyl)as well as chloride, were identified as the photoproducts of the tested PCB usinga GC-ECD, a GC-MS as well as a chloride selective electrode respectively.Excellent mass balance existed between 2,2',4,4'CB and its products. Theseresults indicated that stepwise dechlorination initiated at ortho chlorine was themain photodegradation pathway of the tested PCB congener.By serving as H-atom donor in dechlorination and providing a non-polarsolvent environment fOr dechlorination inside the surfactant micelles, surfactantenhanced photolysis. Only 6% surfactants were decomposed during one hourphotolysis, suggesting surfactants could be reused during photolysis practice inorder to reduce the cost.