Citation:

WONG, C. S., U. PAKDEESUSUK, J. A. MORRISSEY, C. M. LEE, J. T. COATES, A. W. GARRISON, S. A. MABURY, C. H. MARVIN, AND D. C. MUIR. ENANTIOMERIC COMPOSITION OF CHIRAL POLYCHLORINATED BIPHENYL ATROPISOMERS IN DATED SEDIMENT CORES. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 26(2):254-263, (2007).

Impact/Purpose:

To determine the environmental occurrences, fate, and effects of the enantiomers of selected chiral pesticides and other chiral pollutants.

Description:

Enantiomer fractions (EFs) of seven chiral polychlorinated biphenyl (PCB) congeners were measured in dated sediment cores of Lake Hartwell, SC, and Lake Ontario, to detect and quantify microbial reductive dechlorination of PCBs at high and low concentrations, respectively. Lake Hartwell sediments had high total PCB concentrations (5 to 60 micrograms/g), with accumulation and congener patterns consistent with PCB use there. Lake Hartwell sediment EFs were significantly nonracemic, and generally consistent with those from previous laboratory microcosm reductive dechlorination experiments with sediments taken from these sites. These results imply that sediment reductive dechlorination had occurred in situ, including at total PCB concentrations below the 30-80 micrograms/g threshold suggested as necessary for reductive dechlorination. Enantiomer fractions of PCBs 91, 95, 132 and 136 in Lake Hartwell cores were significantly correlated with both concentrations of those individual congeners as well as with total PCB concentration for some sites but not for others. This result suggests that stereoselective microbial dechlorination activity increased with higher concentrations and greater time within sediments, but also that these factors were not the only ones affecting stereoselective dechlorination activity. Comparison of EFs with dates suggest biotransformation half-lives of approximately 30 years, on the same time scale as burial sequestration. Enantiomer composition reversed with depth for PCBs 91, 132, and 176, suggesting there may be multiple microbial populations present within the same core enantioselectively dechlorinating PCBs. In contrast, Lake Ontario sediments (maximum total PCBs 400 nanograms/g) had racemic or near racemic amounts of most congeners throughout the core profile. This result is consistent with achiral indicators suggesting no microbial biotransformation within Lake Ontario sediments, and suggests that thresholds for reductive dechlorination may exist, but at concentrations below 30-80 micrograms/g.

Record Details: