Soil-air exchange model of persistent pesticides in the United States cotton belt

Measurements of organochlorine pesticides (lindane, cis-chlordane [CC], trans-chlordane [TC], trans-nonachlor [TN]), dieldrin, p, p ′-dichlorodiphenyldichloroethylene [DDE], and toxaphene) in Alabama, USA, air and soil were used to assess the soil-air equilibrium status and to identify compounds with significant contributions to observed air burdens. Of the compounds tested, p, p ′-DDE and toxaphene showed a significant potential for outgasing, followed by dieldrin and trans-nonachlor, which showed moderate outgasing potentials. Lindane, cis-chlordane, and trans-chlordane were near soil-air equilibrium. A fugacity-based, multilayered soil-air exchange model was used to predict temporal trends of chemical in air and soil resulting from reemission of soil residues to a presumed clean atmosphere (maximum emission scenario). Results showed that p, p ′-DDE and toxaphene accounted for up to 50% of the observed air burden and that approximately 200 to 600 kg of p, p ′-DDE and 3,000 to 11,000 kg of toxaphene are released to the atmosphere each year by soils in Alabama (area = 1.23 × 1011 m2). High annual net fluxes were also predicted for dieldrin and trans-nonachlor (300-1,100 kg and 150-500 kg, respectively), but these only account for up to ∼20% of their observed air burdens.