Reductive Dechlorination of Polychlorinated Biphenyls in Sediment From the Twelve Mile Creek Arm of Lake Hartwell, South Carolina, Usa

Abstract

Lake Hartwell is a U.S. Army Corps of Engineers reservoir system located on the state line between South Carolina and Georgia, USA. The lake was contaminated with an estimated 200 metric tons of polychlorinated biphenyls ([PCBs]; mainly Aroclor 1016 and 1254), and the entire Twelve Mile Creek watershed and the Seneca River arm of Lake Hartwell were placed on the National Priorities List. Monitored natural attenuation was chosen as a remedy for the contaminated sediment. The relatively warm temperature of Lake Hartwell and lack of significant cocontaminants along with the PCBs distinguish this site from others that have been studied for microbially mediated reductive dechlorination. Microcosm studies were conducted with sediment from two locations in the Twelve Mile Creek arm and confirmed the presence of indigenous microorganisms capable of reductively dechlorinating Aroclor 1254, which contains predominantly tetra-, penta-, and hexachlorobiphenyl. The average number of total chlorines per biphenyl decreased from 4.8 to 4.9 to 2.9 to 3.0, following 250 to 260 d of incubation. The maximum observed dechlorination rates were 0.29 to 0.87 microg-atoms Cl- per gram sediment dry weight per week. The onset of dechlorination activity correlated strongly with maximum methanogenesis, which occurred without a lag in samples from the site that showed signs of in situ fermentation activity. Dechlorination occurred primarily at the meta and para positions (58-63% removal), with no apparent decrease in ortho chlorines. This most closely resembles pattern M, characterized by preferential removal of unflanked and flanked meta chlorines. The microcosm results are consistent with sediment cores analyzed from the same locations, which indicate accumulation with depth of the same ortho- and para-substituted congeners. It therefore appears that the success of monitored natural attenuation for Lake Hartwell will hinge on covering the recalcitrant PCBs with a sufficient amount of uncontaminated sediment to isolate them from the food chain.

Changes in Enantiomeric Fractions during Microbial Reductive Dechlorination of PCB132, PCB149, and Aroclor 1254 in Lake Hartwell Sediment Microcosms

“…Formation of PCB91 and PCB51 from PCB132 indicated a preference for meta dechlorination. This same preference was observed in Lake Hartwell G30 and G33 microcosms spiked with Aroclor 1254 (18,20). Near the end of the incubation period, a low rate of para dechlorination of PCB51 yielded small amounts of 26-2 CB (PCB19) (data not shown).…”

“…Killed controls were prepared identically except that the bottles containing sediment slurry were autoclaved (121°C , 15 min) for three consecutive days prior to addition of the PCBs. Samples of sediment slurry were collected in the anaerobic chamber at various time points to analyze for acetone and organic acids after headspace analysis for CH4 and H2 using the analytical methods described elsewhere (18,20). For PCB analyses, subsamples (3-5 g) were removed and extracted by sonication in acetone (5).…”

“…Four-point calibration curves for identified products were built using aldrin (AccuStandard, Inc.) as an internal standard. PCB congeners in Aroclor 1254 were identified and quantified using the methods described previously (5,18,20,23). Chiral Chromatography.…”

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

“…However, this lake is 22,660 ha in area, compared to the 10 ha of the PI Pond, the major source of PCBs at Lake Hartwell has been closed since 1978, and the sedimentation rate of2 g/cm2/yr (Magar et al 2005a) is probably significantly higher than sedimentation at the PI Pond. As of2003, Lake Hartwell was the only location in the United States where monitored natural attenuation was chosen as a remedy for PCBcontaminated sediment (Pakdeesusuk et al 2003). The cleanup goal is 1.0 mglkg PCBs in the surface 5 cm (Brenner et al 2004) or 10 cm (Magar et al 2005b) of sediment.…”

“…During a 25-year period, peak concentrations in sediments have decreased from 10 to 66 mglkg in buried sediments, to 1 to 3 mglkg in surface sediments (Brenner et al 2004). Pakdeesusuk et al (2003) measured dechlorination rates in sediments of Lake Hartwell. Maximum rates, measured in microcosms ranged from 0.29 to 0.87~g-atoms cr per gram sediment dry weight per week.…”