Emission of legacy chlorinated pesticides from agricultural and orchard soils in British Columbia, Canada

Air samples were collected above agricultural fields in the Fraser Valley and orchards in the Okanagan Valley, British Columbia, Canada, to investigate volatilization of organochlorine pesticides used in the past. Concentrations of pesticides in air were elevated over soils that contained higher residues. Soil/air fugacity ratios at sites with the higher soil residues were calculated relative to air sampled at 40 cm height and background air. The fugacity ratios in the first case indicated net volatilization or soil-air equilibrium for most compounds and occasional net deposition for p,p'-dichlorodiphenyldichloroethene (p,p'-DDE), whereas those in the second case showed a strong potential for net volatilization of all compounds. The enantiomer fraction (EF) of chiral compounds alpha-hexachlorocyclohexane (alpha-HCH), trans-chlordane, cis-chlordane, and o,p'-DDT were determined in overlying air samples and soils. Enantiomer fractions in air corresponded to those in soils at fields in which soil concentrations were high but were decoupled from soil signatures at fields with low soil residues. Mean EFs in air sampled over soils were significantly (p < 0.001) nonracemic for alpha-HCH and the chlordanes and agreed with published EFs in regional ambient air. The mean EF of o,p'-DDT for all air samples did not show a significant deviation from racemic EFs (p > 0.2), but EFs of individual samples reflected the ambivalent nature of o,p'-DDT degradation, sometimes preferring the (+) enantiomer and other times the (-) enantiomer. The study indicates that soils are continuing to emit "legacy" pesticides into the regional atmosphere.