National Water-Quality Assessment (NAWQA) Program
W.T. Foreman, D.A. Goolsby, M.S. Majewski, B.K. Nations, R.H. Coupe, W.W. Larson, and W.A. Battaglin, U.S. Geological Survey, Denver, CO.
In April 1995, a study was undertaken to determine the occurrence and temporal distribution of nearly 50 pesticides and related degradation products in air and rain samples collected in agricultural regions of the Midwestern United States. This investigation included pesticides not examined in previous atmospheric studies. Concurrent high-volume air and wet-only deposition samples were collected weekly at paired urban and rural sites in Mississippi, Iowa, and Minnesota, and at one background location in the upper Michigan peninsula removed from heavy pesticide application. The air samplers consisted of a glass-fiber filter to collect particles and tandem polyurethane foam (PUF) plugs to collect gas-phase pesticides. The filter and PUF plugs were analyzed separately to provide estimates of gas-particle distributions of the pesticides and to establish pesticide collection efficiencies on the PUF plugs. Pesticides in rain samples were isolated by C-1 8 solid-phase extraction. All samples were analyzed by gas chromatography/mass spectrometry using selected ion monitoring. Differences in pesticide concentrations between urban and rural sites and with varying agricultural practices (cropping patterns) from south to north are examined. The relations between air and rain concentrations also are addressed in light of estimated gas-particle distributions of the pesticide in air and other relevant physical properties.