reductive dechlorination of weathered aroclor 1260 during anaerobic biotreatment of arctic soils we investigated the microbial reductive dechlorination of both weathered aged and nonweathered freshly added aroclor 1260 in aerobic soil from resolution island nunavut canada initial polychlorinated biphenyl pcb concentrations were 106 and 100 ppm respectively the aerobic soil samples were inoculated with anaerobic sediment incubated at 30 degrees c until methanogenic inoculated with a dechlorinating enrichment culture and incubated a further 8 weeks the average number of chlorine substituents per biphenyl molecule was biologically reduced from 66 to 51 and from 62 to 45 for weathered and nonweathered aroclor 1260 respectively removal of hexa and heptachlorobiphenyls cbs the major homolog groups present was significantly greater for nonweathered than for weathered aroclor 1260 formation of dechlorination products primarily 2244 and 2246tetracbs was also significantly greater for nonweathered than for weathered aroclor 1260 we additionally compared the dechlorination at 21 degrees c of weathered aroclor 1260 in soils from resolution island and saglek labrador canada the average number of chlorine substituents per biphenyl molecule was biologically reduced from 67 to 51 and from 65 to 46 respectively this study demonstrated the potential for bioremediation of aerobic soil contaminated with aroclor 1260 and showed that weathering may limit such treatment to an extent variable among different soils