| Polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants once used as industrial fluids (in hydraulic systems, gas turbines), dielectric fluids (capacitors, transformers), plasticizer (adhesives, textiles, sealants, copy paper), and heat exchangers due to their inertness as well as thermal and electrical insularity. However, they are found to be neurotoxic, immunosuppressive, hepatotoxic, and the USEPA classified PCBs as probable human carcinogens. Although the production of PCBs was banned by the US Congress in 1976, they persist in the environment because of their resistance. Upon entering the marine environment, PCBs will associate with particulates and ultimately with sediment due to their hydrophobic nature and thus sediment become a sink for PCBs. This exerts a threat to marine organisms and human who consume seafood.; Photolysis utilises short wavelength ultraviolet radiation to excite and cleave the carbon-chlorine bond of PCBs, yielding less chlorinated PCBs and ultimately biphenyl which can serve as energy and carbon source of various bacteria. Thus integration of photolysis and biodegradation can be a feasible remediation for PCB contamination.; The major sink of PCBs in the environment is marine sediment, and the presence of sediment particles as well as other sorbed chemicals may inhibit both photolysis and biodegradation. This study extracts PCBs from sediment and further purify them by various cleanups to prevent the effect of these materials on the efficiency of treatment.; Using 2,4,4'-trichlorobiphenyl (PCB 28), 2,2',5,5'-tetrachlorobiphenyl (PCB 52), 2,2',4,5,5'-pentachlorobiphenyl (PCB 101), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) and 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB 180) as model compounds, optimal UV intensity, reaction time, as well as reaction solvent were found to be dependent on the congeners used. While PCB 28 was highly reactive and PCB 101, PCB 153 and PCB 180 were comparatively easy to remove, PCB 52 showed high resistance towards photolysis. The photolysis of PCB mixture containing these five congeners with each of them in 1 mg/L was also being optimised. After optimisation, the reaction intermediates and products were identified by gas chromatography coupling mass spectrometry (GC-MS). Less chlorinated congeners and biphenyl were found, indicating stepwise dechlorination of PCB is the major pathway. (Abstract shortened by UMI.)... |
