EFFECT OF AROCLOR-1248 CONCENTRATION ON THE RATE AND EXTENT OF POLYCHLORINATED BIPHENYL DECHLORINATION

Dechlorination kinetics of polychlorinated biphenyls (PCBs) were inves tigated in Aroclor 1248-spiked sediments at 16 concentrations ranging from 0 to 200 ppm using sediment microorganisms from the Reynolds site in the St. Lawrence River, New York, USA, over a 58-week incubation p eriod. The time course of dechlorination, measured as the total Cl per biphenyl, consisted of an initial lag phase followed by rapid dechlor ination and then a plateau that represented an apparent endpoint of de chlorination. A clear threshold concentration was found between 35 and 45 ppm; there was no dechlorination observed at seven concentrations below this level. Above the threshold concentration, dechlorination ra te was a function of sediment PCB concentration. The rate, calculated as the slope of the rapid phase, was linear within the concentration r ange investigated. The maximum extent of dechlorination also increased with initial Aroclor concentrations; only 4% of Cl per biphenyl was r emoved at 35 ppm, and the removal was saturated at approximately 36% a bove 125 ppm. This difference appeared to be due to whether or not dec hlorination involved meta-rich congeners such as 25-2' (IUPAC no. 18), 25-2'5'- (no. 52), and 23-2'5' chlorobiphenyl (no. 44). These results indicate that a major controlling factor for natural remediation pote ntial in sediments is the initial PCB concentration that determines th e maximum extent of dechlorination rather than the dechlorination rate .