Chiral organochlorine pesticides in the atmosphere

We measured the enantiomeric fractions (EF) of various organochlorine pesticides in air samples from Indiana, Arkansas, and Louisiana collected in 2002–2003. Enantiomeric fractions for o,p′-DDD are reported here for the first time, and they suggest preferential depletion of one enantiomer over the other, with a mean value of 0.44. For the chlordanes, the EFs followed the same trends as reported in previous studies. EF values for trans-chlordane (TC) were slightly below 0.5, and values for cis-chlordane (CC) were slightly above 0.5. For cis-heptachlor epoxide (HEPX), the EF values averaged 0.65, indicating a clear preferential depletion of the (−)-enantiomer. For TC and CC, no clear distinction could be made between the values measured among the three sites, suggesting that it is not possible to use these EF values as “source signatures”. For HEPX, the Indiana site had significantly higher EF values than did the Arkansas site; this difference may reflect differences in the historic use of heptachlor in these two regions.