Environmental Fate of Legacy Chiral Pesticides in Background Soils

Variability in the enantioselective degradation of chiral organo- chlorine pesticides (OCPs: D -HCH, cis- and trans-chlordane (CC and TC), chlordane MC5 and o,pc-DDT) in background soils was investigated on a global scale and in small-scale transect studies. Background soils collected from 32 countries displayed a wide range of enantiomer profiles for a particular compound, showing varying degradation preferences. In some locations, grassland and woodland soils which were collected only a few hundred meters apart showed differences in the enantiomer profiles and even reversals in degradation preferences. Further studies at small plots in Scotland indicated that such differences could be found within a few meters horizontally and a few centimeters in depth. Soil organic matter content and pH exerted a minor influence on the variability. For chlordanes, the enantiomer profiles in background soils were much more variable than those in ambient air, suggesting that degradation occurred following atmospheric deposition. Thus, background soils play a role in sequestering and degrading OCPs, although enantiomer profiles are not a quantitative measure of overall degradation. The results of this study show that caution is needed when considering the enantiomer signatures in air as a marker of volatilization of weathered soil-derived OCPs.