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Enantiomeric composition of chiral polychlorinated biphenyl atropisomers in dated sediment cores
Author(s) -
Wong Charles S.,
Pakdeesusuk Usarat,
Morrissey Joshua A.,
Lee Cindy M.,
Coates John T.,
Garrison Arthur W.,
Mabury Scott A.,
Marvin Christopher H.,
Muir Derek C. G.
Publication year - 2007
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/06-164r.1
Subject(s) - reductive dechlorination , polychlorinated biphenyl , environmental chemistry , enantiomer , biotransformation , chemistry , microcosm , sediment , biphenyl , atropisomer , composition (language) , biodegradation , geology , organic chemistry , enzyme , paleontology , linguistics , philosophy
—Enantiomer fractions (EFs) of seven chiral poly chlorinated biphenyls (PCBs) were measured in dated sediment cores of Lake Hartwell (SC, USA) and Lake Ontario (USA) to detect, quantify, and gain insight regarding microbial reductive dechlorination of PCBs in lake sediments with high and low concentrations, respectively. Lake Hartwell sediments had high total PCBs (5–60 μg/g), with significantly nonracemic EFs that generally were consistent with those from previous laboratory microcosm reductive dechlorination experiments using sediments from these sites. Thus, stereoselective reductive dechlorination had occurred in situ, including at total PCB concentrations of less than the threshold of approximately 30 to 80 μg/g suggested as being necessary for reductive dechlorination. Enantiomer fractions of PCBs 91, 95, 132, and 136 in Lake Hartwell cores were significantly correlated both with concentrations of those individual congeners and with total PCB concentration for some sites. This result indicates that enantioselective microbial dechlorination activity increases with higher concentrations within sediments for these congeners. Enantiomer composition reversed with depth for PCBs 91, 132, and 176, suggesting that multiple microbial populations may be present within the same core that are enantioselectively dechlorinating PCBs. Such observations indicate that concentration and time are not the only factors affecting biotransformation, complicating prediction of enantioselectivity. Comparison of EFs with dates suggested biotransformation half‐lives of approximately 30 years, which is on the same time scale as sequestration by burial. In contrast, Lake Ontario sediments (maximum total PCBs, 400 ng/g) had racemic or near‐racemic amounts of most congeners throughout the core profile, which is consistent with achiral indicators suggesting no microbial biotransformation within Lake Ontario sediments. Thresholds for reductive dechlorination may exist, but they would be at concentrations of less than 30 to 80 μg/g.