Enantiomeric Ratios of Chlordane-Related Compounds in Air near the Great Lakes

Some important environmental contaminants are chiral; therefore, enantiomeric ratios (ER) of these compounds can provide useful insights into their environmental fates. In this study, permethylated α- and γ-cyclodextrin gas chromatographic columns combined with electron capture and negative ionization mass spectrometry were used to measure the ER values of chlordane and related compounds. These techniques provided the selectivity and sensitivity necessary for these low-level environmental determinations. Studies using racemic and enriched standards confirmed that this analytical system gave reproducible and accurate ER measurements. From August 1994 through September 1995, 48 air samples were taken near Lake Erie, five air samples were taken near Lake Michigan, and six air samples were taken near Lake Superior. These samples were analyzed to determine the spatial trends in ER values. While there were slight differences between the various sites, there were considerable dif ferences between the compounds. The overall ER for cis -chlordane was 1.05 ± 0.02, which is close to racemic. The overall ER for trans -chlordane was 0.88 ± 0.02, which is significantly different than racemic and from the measured cis -chlordane value. This discrepancy suggests that trans - and cis -chlordane are metabolized differently in the environment. The overall ER of exo -heptachlor epoxide was 1.99 ± 0.04; this large deviation from racemic indicates that this compound is an enzymatic degradation product of heptachlor.