Submitted to: International Congress of Pesticide Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 30, 2002
Publication Date: August 4, 2002
The environmental fate of airborne organic pollutants, i.e., atmospheric lifetime, is often governed by their distribution between the vapor and particle phases. An accurate understanding of the chemical-specific air-particle interactions is necessary to predict the distance a particular chemical may travel from its source and the loadings it may contribute to non-target regions. Air samples were collected in two different agricultural watersheds within the larger Chesapeake Bay system. Sample extracts were analyzed for a number of commonly used agricultural pesticides, but atrazine and metolachlor were observed most frequently in both the gas and particle phases. This project is an examination of these two chemicals with respect to trends in concentration, vapor-particle distribution, and a comparison of observed (fobs) vs. predicted particle-phase fractions (fpred) using the Junge-Pankow and Octanol-Air approaches. Values of fobs were about 1.4-15 and 0.67-53 times as high as fpred values for atrazine and metolachlor, respectively, indicating that the model underestimates the sorption of these polar chemicals to aerosols. Alternatively, this may indicate that atrazine and metolachlor are not at equilibrium in the atmosphere. The differences between fobs and fpred were largest during the late spring and summer when the herbicides are applied. There are two main mechanisms by which pesticide residues are transported into the atmosphere from soil after application: one is volatilization, and the other is wind erosion. However, it is generally considered that wind erosion plays a less important role than volatilization. The difference between observed and predicted fractions of observed particle phase distribution for atrazine and metolachlor in summer may suggest that while pesticide evaporation or sublimation after application is an important source to airborne pesticide contamination, pesticide residue attached to soil particles and transported into the atmosphere via wind erosion may also play an important role, especially in areas close to intense agricultural activity.