Selective Persistence and Bioaccumulation of Toxaphene in a Coastal Wetland

Enviro Toxic and Chemistry

Bartha

Stern

et al. 1999

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The composition of toxaphene residuesand the enantiomeric ratios of the major congeners were studied in the top 10 slices (1935–1992) of a sediment core collected from Hanson Lake in the Yukon Territories (Canada). This lake was treated with toxaphene as a picsicide in July 1963. Electron‐capture negative ion mass spectrometry and electron‐capture detection were applied in combination with enantioselective gas chromatography using modified cyclodextrin columns. Of the 10 toxaphene peaks identified in each of the sediment slices, two congeners, 2‐exo,3‐endo,6‐exo,8,9,10‐hexachlorobornane (B6‐923 or Hx‐Sed) and 2‐endo,3‐exo, 5‐endo,6‐exo, 8,9,10‐heptachlorobornane (B7‐1001 or Hp‐Sed), were the most abundant. Each of the three chiral stationary phases used in this study was successful at resolving the enantiomers in at least of one of the two congeners. Among them was permethylated β‐cyclodextrin (Chirasil‐Dex), which, up until now, has never been used for enantiomer separation of compounds of technical toxaphene. B6‐923 and another less abundant, as of yet unknown, hexachlorobornane were racemic in all sediment core slices. For B7‐1001, the latter eluting enantiomer was always more predominant. Furthermore, the enantiomeric ratio was found to consistently decrease with time from approximately 0.8 in the early slices (∼1950) to 0.7 in the slice representing 1992, implying that the first eluted B7‐1001 enantiomer is less persistent than the second. B6‐923 and B7‐1001 are most likely metabolites of the more highly chlorinated congeners. A structural evaluation provided evidence that reductive dechlorination at carbons with geminal chlorine atoms is the primary microbial degradation pathway in sediments from Hanson Lake.

Section: Discussionmentioning

confidence: 99%

Enantioselective determination of two persistent chlorobornane congeners in sediment from a toxaphene‐treated yukon lake

Enviro Toxic and Chemistry

Bartha

Stern

et al. 1999

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“…Individual CTT concentrations were computed from the average response of a 22-component mixture (TM2; Dr. Ehrenstorfer, Germany) (5 point calibration; r 2 > 0.99). The response factors for B6-923 and B7-1001 were assumed to be equal to the mean of all 22 components in TM2 (19).…”

Section: Methodsmentioning

confidence: 99%

“…Quality Assurance/Quality Control (QA/QC). Provisions for QA/QC, including the analysis of procedural blanks, spiked reference sediment and tissue, and replicate samples, are outlined elsewhere ( , ). On the basis of blank values and instrument sensitivity, the nominal detection limit for individual congeners was ∼1 ng/g.…”

Section: Methodsmentioning

confidence: 99%

Interpreting Nonracemic Ratios of Chiral Organochlorines Using Naturally Contaminated Fish

Smalling

Maruya

2001

Environ. Sci. Technol.

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Although reports of nonracemic proportions of chiral organochlorine pollutants in the environment are widespread, the interpretation of such data is not well developed. Using GC/MS and a chiral stationary phase consisting of 25% tert-butyldimethylsilylated beta-cyclodextrin in PS086 (beta-BSCD), we followed the change in the enantiomeric signature of 2-exo,3-endo,6-exo,8,9,10-hexachlorobornane (B6-923) in naturally contaminated fish maintained under toxaphene-free conditions. Whereas the enantiomeric ratio (ER) of B6-923 was near racemic at the start of the elimination experiment, it had increased severalfold by the end of 60 d. On the basis of first-order kinetics, one enantiomer of B6-923 was eliminated twice as fast as its mirror image, resulting in half-lives of 7 and 13 d, respectively. Enantioselective elimination by our test fish (Fundulus sp.) strongly suggests active biotransformation of B6-923; however, bioprocessing throughput estimates suggest a very low in situ rate of natural attenuation. These results confirm that the relatively constant ERs observed for chiral organochlorines in a given species are the result of competing processes, e.g., uptake vs elimination. Our experiments also further illustrate the utility of enantioselective analysis in characterizing the biotransformation of persistent organochlorine pollutants.

“…However, relatively little is known about the CTT elimination and metabolic transformation processes associated with midlevel aquatic organisms such as fish. Analysis of preliminary data on the levels of toxaphene residues in marsh biota collected synoptically with the sediments in this study indicated that B6‐923 and B7‐1001 are also among the most prominent CTTs [14], indicating that source characteristics (i.e., sediment) are important. Preliminary evidence also exists that enantiomer ratios of prominent CHBs in these biota were shifted significantly relative to sediments, suggesting that biotransformation is occurring [25].…”

Section: Resultsmentioning

confidence: 99%

“…The concentrations of individual CHB congeners and total toxaphene (⌺TOX) in sediment were quantified using GC-ECD, the details of which are given elsewhere [14]. Briefly, congener-specific concentrations were computed using mean response factors (2-100 pg calibration range) based on the TM2 22-component mixture (Dr. Ehrenstorfer, Augsburg, Germany).…”

Section: Gas Chromatography-mass Spectrometry (Gc-ms) and Gc-electronmentioning

confidence: 99%

Prominent chlorobornane residues in estuarine sediments contaminated with toxaphene

Maruya

Wakeham

Enviro Toxic and Chemistry

et al. 2000

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Abstract-Soils and sediments contaminated with residues of technical toxaphene may require remedial action to reduce human health and ecological risks. Sediments were collected from a coastal wetland impacted by discharge from a former toxaphene production facility and analyzed by gas chromatography-electron capture detection and conventional and enantioselective gas chromatography-mass spectrometry in the electron capture negative ion mode. The prominent chlorobornanes (CHBs) in all samples were 2-exo,3-endo,6-exo,8,9,10-hexachlorobornane (B6-923 or Hx-Sed) and 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane (B7-1001 or Hp-Sed), metabolites of higher chlorinated components of technical toxaphene (CTTs). Pentachlorobornanes, toxaphene homologs not previously reported in environmental samples, and likely precursor CTTs were also detected. Several CHB congeners were enantioresolved, the majority of which exhibited racemic composition. These results indicate that the profile of CHBs persisting in estuarine sediment is highly modified relative to the technical mixture, and also provides strong evidence of in situ reductive dechlorination, a process that if enhanced could act to reduce bioaccumulation and toxicity of sediment-bound CTTs at toxaphenecontaminated sites.