REDUCTIVE DECHLORINATION OF AROCLOR 1242 IN ANAEROBIC SEDIMENTS - PATTERN, RATE AND CONCENTRATION-DEPENDENCE

Anaerobic biotransformation of polychlorinated biphenyls of Hudson Riv er sediment microorganisms was investigated using the commercial mixtu re Aroclor 1242 in the laboratory at six different concentrations: 120 , 300, 500, 800, 1,000, and 1,500 mug/g (on a sediment dry-weight basi s). Dechlorination was concentration dependent. No change in congener composition was found at 1,000 and 1,500 mug/g during seven months of incubation, but significant shifts were observed in sediments with con centrations below 800 mug/g. A mass balance of the transformation indi cated that, despite the shifts, the total molar concentration remained the same. An optimum concentration, based on the decrease of Cl per b iphenyl, was 500 mug/g, but based on Cl removed per gram sediment it h ad a range from 500 to 800 mug/g. Dechlorination (total Cl removed per biphenyl) at 300 and 500 mug/g appeared to be first order, with rate constants of -0.039 and -0.059 per month, respectively. The rate also varied with the substitution position; it was faster for m-Cl, followe d by p-Cl, but no o-Cl was removed. However, the faster rate of m-dech lorination in Aroclor 1242 was probably due to a high concentration of congeners in the Aroclor with Cl substitution patterns favoring its r emoval, rather than the meta-position itself.