Determination, mobilization and dechlorination of polychlorinated biphenyl (PCB) compounds in contaminated soils

Polychlorinated biphenyls (PCBs) are a group of 209 chemical congeners that are toxic and persistent organic contaminants that have been present in the environment for several decades. It has been estimated that some 11 million tons of PCBs have contaminated soil, sediments, vegetation and animals. About 300 million tons of PCBs, that remain in use in North America, represent a potential source of contamination that can further deteriorate the environment.; Due to their toxicity, physical and chemical stability and environmental persistence, PCBs have attracted a great deal of attention and have encouraged researchers to develop new techniques/approaches to detoxify PCBs and PCB contaminated matrices in a rapid, efficient and environmentally friendly manner. In 2000, the market for PCB treatment technologies is estimated to be {dollar}300--{dollar}600 million (Canadian) dollars.; This study investigated novel approaches/techniques for PCB dechlorination with zero-valent metals or bimetallic mixtures; optimised a method for PCB determination within contaminated soil/sediments and PCB washing/flushing from contaminated soil. Soil washing/flushing was combined with supercritical carbon dioxide (ScCO2) mobilization dechlorination on-line using zero-valent metals. Studies have demonstrated that PCB can be dechlorinated efficiently by heated columns of zero-valent metal or bimetallic mixtures. The limit of detection for PCBs within contaminated soil was estimated to be 0.15 mg/kg for a simple procedure that converted PCB residues to biphenyl. PCBs were flushed efficiently from polluted soils into surfactant suspension and then back-extracted into supercritical CO2. Finally, they were dechlorinated virtually quantitatively in a continuous on-line process using heated columns of zero-valent bimetallic mixtures. The dechlorination yield for PCB extracts from contaminated soil or from PCB surfactant mixture was greater than 99.5%. The treated surfactant suspensions could be recycled to extract more PCBs from the contaminated soil. The techniques/approaches developed in this study would seem to have a broad application in PCB dechlorination/detoxification and in the remediation of historically contaminated soil/sediments.