Effects of Organic Substrates on Dechlorination of Aroclor 1242 in Anaerobic Sediments

Bush

et al. 1993

The effect of electron acceptors and biphenyl on reductive dechlorination was investigated using the commercial polychlorinated biphenyl mixture Aroclor 1242 and sediment microorganisms from the Hudson River. Polychlorinated biphenyl‐ (PCB‐) free sediments spiked with the Aroclor at 700 μg/g and anaerobically incubated for six months, with and without biphenyl enrichment, showed that dechlorination was most advanced with CO2 without biphenyl enrichment. A small amount of methane was detected. However, methane production per se was not essential for dechlorination, because addition of the inhibitor of methane production, 2‐bromoethane sulfonate, did not affect dechlorination. On the other hand, dechlorination was inhibited partly by sulfate and completely by nitrate. Biphenyl enrichment initially inhibited dechlorination under both methanogenic and sulfidogenic conditions.

Section: Resultsmentioning

confidence: 99%

Anaerobic dechlorination of aroclor 1242 as affected by some environmental conditions

Bush

et al. 1993

“…When trying to extrapolate laboratory findings to the natural environment, it is important to keep in mind the wide variation in PCB concentrations and vast heterogeneity in chemical composition in river sediments, because dechlorination was concentration dependent in the present study and elsewhere [21] and also was dependent on the availability of organic substrates [23]. Contaminated sediments that do not contain essential organic matter and/or nutrients may remain immune to dechlorination.…”

Section: Microorganisms Eluted From Upper Hudsonmentioning

confidence: 99%

Reductive dechlorination of aroclor 1242 in anaerobic sediments: Pattern, rate and concentration dependence

Bush

et al. 1993

Anaerobic biotransformation of polychlorinated biphenyls of Hudson River sediment microorganisms was investigated using the commercial mixture Aroclor 1242 in the laboratory at six different concentrations: 120, 300, 500, 800, 1,000, and 1,500 μg/g (on a sediment dry‐weight basis). Dechlorination was concentration dependent. No change in congener composition was found at 1,000 and 1,500 μg/g during seven months of incubation, but significant shifts were observed in sediments with concentrations below 800 μg/g. A mass balance of the transformation indicated that, despite the shifts, the total molar concentration remained the same. An optimum concentration, based on the decrease of Cl per biphenyl, was 500 μg/g, but based on Cl removed per gram sediment it had a range from 500 to 800 μg/g. Dechlorination (total Cl removed per biphenyl) at 300 and 500 μg/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, followed by p‐Cl, but no o‐Cl was removed. However, the faster rate of m‐dechlorination in Aroclor 1242 was probably due to a high concentration of congeners in the Aroclor with Cl substitution patterns favoring its removal, rather than the meta‐position itself.

“…

Reductive dechlorination of PCBs by Hudson River sediment microorganisms was investigated using individual congeners,2,3,4,2',4,2,4,5,2',4',2,3,4,5,2,4,2',and 3,4,3',4'chlorobiphenyls (CBPs) in long-term studies lasting 15 to 20 months. The dechlorination of 2, 3,4,2',4,4,5,2',2,4,2',2,4,2',and 2,4,2'-CBPs; notably absent was 2,2'-CBP. Yet, the total molar concentration of all congeners decreased with time and at 15 months accounted for only 25% of the initial concentration of the parent compound.

…”

mentioning

confidence: 99%

A long‐term study of anaerobic dechlorination of PCB congeners by sediment microorganisms: Pathways and mass balance

Bethoney

et al. 1993

Reductive dechlorination of PCBs by Hudson River sediment microorganisms was investigated using individual congeners, 2,3,4,2′,4′,5′‐, 2,4,5,2′,4′,5′‐, 2,3,4,5,6‐, 2,4,2′,4′‐, and 3,4,3′,4′‐chlorobiphenyls (CBPs) in long‐term studies lasting 15 to 20 months. The dechlorination of 2,3, 4,2′,4′,5′‐CBP yielded 2,4,5,2′,4′‐, 2,4,2′,4′‐, 2,4,2′,5′‐, and 2,4,2′‐CBPs; notably absent was 2,2′‐CBP. Yet, the total molar concentration of all congeners decreased with time and at 15 months accounted for only 25% of the initial concentration of the parent compound. 2,3,4,5,6‐CBP produced 2,3,5,6‐, 2,4,6‐, and 2,6‐CBPs. At 15 months the sum of all congeners accounted for only about 50% of the initial amount of the parent congener. On the other hand, 2,4,5,2′,4′,5′‐CBP yielded six daughter products, including 2,2′‐CBP, and did not show any decrease in total molar concentration even at 20 months. 2,4,2′,4′‐CBP did not show any change at 15 months. These results indicate that anaerobic PCB biotransformation may include mechanisms other than dechlorination and that the mechanisms are congener dependent. Biphenyl was detected with 3,4,3′,4′‐CBP, indicating complete dechlorination; however, it accounted for < 10% of the total molar loss. 14C‐labeled tracer of this congener showed that all radioactivity was in the hexane fraction, suggesting that transformation products were hydrophobic.