Interpreting nonracemic ratios of chiral organochlorines using naturally contaminated fish

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.