Effect of aroclor 1248 concentration on the rate and extent of polychlorinated biphenyl dechlorination

Abstract

Abstract-Dechlorination kinetics of polychlorinated biphenyls (PCBs) were investigated 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 period. The time course of dechlorination, measured as the total Cl per biphenyl, consisted of an initial lag phase followed by rapid dechlorination and then a plateau that represented an apparent endpoint of dechlorination. 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 rate was a function of sediment PCB concentration. The rate, calculated as the slope of the rapid phase, was linear within the concentration range investigated. The maximum extent of dechlorination also increased with initial Aroclor concentrations; only 4% of Cl per biphenyl was removed at 45 ppm, and the removal was saturated at approximately 36% above 125 ppm. This difference appeared to be due to whether or not dechlorination involved meta-rich congeners such as 25-2Ј (IUPAC no. 18), 25-2Ј5Ј-(no. 52), and 23-2Ј5Ј chlorobiphenyl (no. 44). These results indicate that a major controlling factor for natural remediation potential in sediments is the initial PCB concentration that determines the maximum extent of dechlorination rather than the dechlorination rate.

Enhancement of microbial PCB dechlorination by chlorobenzoates, chlorophenols and chlorobenzenes

“…Sediment slurries in serum vials were autoclaved and then amended with each of the non-PCB HACs (3-, 2,3-, 2,4-, 2,5-, 2,3,5-and 2,4,6-chlorobenzoate; 2,3-, 3,4-, 2,5-, 2,3,6-and penta-chlorophenol ; and 1,2-, 1,2,3-, 1,2,4-and penta-chlorobenzene) in acetone stock solutions (0.5%, v/ v) to yield a ¢nal concentration of 200 Wg (g sediment) 31 . To obtain an inoculum of natural sediment populations, 10 g of the Reynolds site sediments was ¢rst made into slurries in 100 ml of sterilized and reduced synthetic mineral medium, and then stirred for 1 h. After allowing these slurries to settle for 20 min, the supernatant was used as the inoculum.…”

“…For laboratory studies, PCB-contaminated sediments were prepared in serum vials by spiking PCB-free sediments with Aroclor 1248 in hexane to yield a concentration of 300 Wg (g sediment) 31 (dry weight basis). The hexane was removed by evaporation.…”

Evaluation of the Eological Management and Enhancement Alernative for Remediation of the K1007-P1 Pond

“…Rates of biotransformation are generally directly proportional to solution concentrations rather than total concentrations in sediment (Zwiemik et al 1999), though Sokol et al (1998) found that above concentrations of35 to 45 mg/kg, the dechlorination rate of Aroclor 1248-spiked St. Lawrence River sediments was proportional to concentration in sediment. Because solution concentrations for most congeners are in the low nanogram per liter concentration, transformation rates can be very low.…”

“…In this case, rates would be slow and difficult to measure, but perhaps significant over multi-year periods. Similarly, Sokol et al (1998) cite studies where dechlorination occurred at PCB concentrations as low as 10 mg/kg sediment and possibly in the ppb range, with bioavailability suggested as the explanation for different thresholds at different sites. PCB dechlorination at Lake Hartwell, SC, apparently occurs at sediment concentrations much lower than 50 mg/kg (Magar et al 2005b).…”

“…Although aging sometimes affects the bioavailability and transformation rates of organic compounds, the dechlorination of PCBs aged in sediments occurs at rates similar to those in freshly spiked sediments (Abramowicz et al 1993). Sokol et al (1998) argue that "a major controlling factor for natural remediation potential in sediments is the initial PCB concentration that determines the maximum extent of dechlorination rather than the dechlorination rate." They observed a threshold for dechlorination at concentrations at about 35 to 45 mg/kg, with reactions not occurring below those concentrations.…”