R P
s on the
System CARINA GRITTIN1,I MARK MALCOMSON,' QUINTUS FERNANDO,*,' AND NIC KORTE* Department of Chemiso, University of Arizona, Tucson, Arizona 85721, and Environmental Sciences Division, Oak Ridge National Laboratory, Grand Junction Office, Grand Junction, Colorado 85103
Introduction Polychlorinated biphenyls (PCBs) are a group of synthetic aromatic compounds with the general formula C12H10-xClr that have been widely used because of their excellent dielectric properties and their resistance to heat and chemical degradation (1). PCBs have been introduced into the environment via improper disposal and accidental leaks from transformers, heat exchangers,and hydraulic systems. PCBs in the environment are transported primarily by particulate matter containingthe adsorbed compounds and as a consequence are dispersed worldwide. The uptake of PCB-contaminated sediments by biota at the watersediment interface can introduce PCBs into the food chain and may cause serious health problems in humans. It is of utmost importance, therefore, to seek effectivemethods to remove PCBs from the environment. We report here a simple method for the rapid and complete dechlorination of a methanol-water solution containing all the congeners of PCBs present in the commercially available mixtures Aroclor 1260and Aroclor 1254. The dechlorinationreaction occurs at ambient temperatures on the surface of palladized iron, a PdlFe bimetallic system that has been found to rapidly dechlorinate one- and two-carbon chlorinated compounds (2). The reaction products are biphenyl and chloride ions. At present there are no widely accepted methods for the remediation of water or soils contaminated with PCBs. Incineration of soils containing PCBs at temperatures below 700 "C results in the formation of volatile hazardous compounds such as dioxins (3).Therefore, much higher temperatures are required to completely decompose PCBs without the formation of hazardous intermediate compounds. The aerobic and anaerobic biodegradation of PCBs in soil with various types of microorganisms have been successfully accomplished in laboratory studies, but the reactions require months and depend on the ability of the * Author to whom all correspondence should be addressed. University of Arizona. Oak Ridge National Laboratory.
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microorganisms to survive in systems containing the chlorinated organic compounds (4- 7). Likewise, chemical methods require elevated temperatures and long reaction times (8-11). Elemental iron, for example, requiredtemperatures of approximately 400 "C for dechlorination of PCBs (12). A recently published chemical method (13) requires a temperature of 125 "C and about 24 h for the complete reductive dechlorination of PCBs by the use of sodium borohydride as the reducing agent in the presence of an amine such as pyridine and titanocene dichloride as a catalyst in a nonaqueous medium, e.g., triglyme. The electrolytic dechlorination of PCBs appears to be a promising method for remediation of PCB-containing soils at ambient temperatures (14), but several hours are required for complete dechlorination even in the presence of zinc phthalocyanine, which is used as a catalyst to enhance the efficiency of the electrolysis.
Experimental Section Approximately 2 g of iron particles (
