Copyright © 1999 American Chemical Society
Enantioselective metabolism of
-HCH, the only chiral HCH isomer,
takes place in lakes and marine waters. Nonracemic residues of
-HCH, o,p'-DDT, chlordane, and the metabolites heptachlor epoxide and oxychlordane were found in agricultural soils (3). Preferential accumulation of pesticide enantiomers and alteration of enantiomer ratios (ERs) have also been observed in biota (2, 5). Metabolic
processes do not always favor the same enantiomer, as exemplified
in studies with -HCH (2). The (+) enantiomer is preferentially degraded in some cases and the (-) enantiomer in others (signs refer
to the direction of optical rotation). Residues of -HCH in biological
tissues show preferential accumulation of either enantiomer, depending on the organism (2, 5), and strong preferential accumulation of (+) -HCH in seal brain tissue appears to be due to its ability
to selectively penetrate the blood-brain barrier (2). Ambivalence
was also seen for o,p'-DDT in midwestern U.S. soils, with depletion
of the (+) enantiomer in some soils and the (-) enantiomer in others
(3). Reasons for these reversals are not known but may be related
to different microbial populations in environmental media. Enantioselective metabolism takes place not only for OC pesticides, but for
other chiral compounds as well.
