Atmospheric transport and air-surface exchange of pesticides

Atmospheric transport and exchange of pesticides with soil, vegetation, water and atmospheric particles are discussed, with an emphasis on applying physicochemical properties of the compound to describe environmental partitioning. The octanol-air partition coefficient is promoted as a unifying property for describing volatilization of pesticides from soil and sorption to aerosols. Present-day sources of organochlorine (OC) pesticides to the atmosphere are continued usage in certain countries and volatilization from contaminated soils where they were used in the past. Models are available to predict volatilization from soil; however, their implementation is hampered by lack of soil residue data on a regional scale. The need to differentiate "new" and "old" sources is increasing, as countries negotiate international controls on persistent organic pollutants (POPs). A new technique, based on the analysis of individual pesticide enantiomers, is proposed to follow emission of chiral OC pesticides from soil and water. Air monitoring programs in the Arctic show the ubiquitous presence of OC pesticides, PCBs and other POPs, and recently a few "modern" pesticides have been identified in fog and surface seawater. Atmospheric loadings of POPs to oceans and large lakes take place mainly by air-water gas exchange. In the case of OC pesticides and PCBs, aquatic systems are often near air-water equilibrium or even oversaturated. Measurement of water/air fugacity ratios suggests revolatilization of PCBs and several OC pesticides in the Great Lakes and, for α-hexachloroacyclohexane (α-HCH), in the Arctic Ocean. Outgassing of α-HCH in large lakes and arctic waters has been confirmed by enantiomeric tracer studies. The potential for pesticides to be atmospherically transported depends on their ability to be mobilized into air and the removal processes that take place enroute: wet and dry deposition of gases and particles and chemical reactions in the atmosphere. Measurement of reaction rate constants for pesticides in the gas and particle phase at a range of environmental temperatures is a critical research need. The transport distance of a chemical is related to its overall environmental persistence, determined by the partitioning among different compartments (water, sediment, soil, air), degradation rates in each compartment and mode of emission (into water, soil, air). Several pesticides found in the arctic environment have predicted lifetimes in the gas phase of only a f