Effects of selected reducing agents on microbiologically mediated reductive dechlorination of aroclor® 1242

Abstract The effect of various chemical reducing agents on the anaerobic microbial reductive biotransformation of polychlorinated biphenyls (PCBs) was investigated using Aroclor® 1242 at a concentration of 600 μg/g soil and microorganisms eluted from Hudson River sediments. The investigation sought to determine how various reducing agents influenced PCB dechlorination rates, patterns, and acclimation periods. Three reducing agents were incorporated into culture media: amorphous ferrous sulfide, sodium sulfide with sodium thioglycollate, and sodium sulfide with amorphous ferrous sulfide. All cultures were incubated statically under methanogenic conditions and ambient incubation temperatures of about 20°C. Cultures utilizing both sodium sulfide and ferrous sulfide together demonstrated the most extensive removal of meta- and para-chlorines, the highest average dechlorination rate, the greatest dechlorination of tri- and tetrachlorinated biphenyls, and the greatest accumulation of dichlorobiphenyl homologues. Overall, treatments incorporating ferrous sulfide, alone or in combination with sodium sulfide, demonstrated the ability to more effectively dechlorinate tri-ortho-substituted tetrachlorobiphenyls and pentachlorobiphenyls which had commonly positioned chlorines. Under these same conditions, dichlorobiphenyls, which are more amenable to aerobic dechlorination conditions, increased from 25% (molar basis) initially to levels greater than 60%.