Pesticides in the atmosphere in Minnesota: Partitioning, deposition, and significance

The atmosphere is recognized as an important pathway by which pesticides are transported and deposited in the areas far from their sources. The observations of pesticides in rain, air, and surface runoff in Minnesota (1993--1996) contribute to understand the significance of the atmospheric deposition.;The vapor/particle partitioning of pesticides in the urban area of Minnesota elucidated a strong dependency on the subcooled liquid vapor pressure, but not the same as predicted by Junge's model. The air concentrations before and after a single 24-hour rain event indicated that rain scavenging is efficient for removing water-soluble herbicides. Concentrations of many herbicides in 43 sequential rain samples followed the same pattern: much higher concentration at the beginning of the rain than that in the rest of rain event.;The most frequently detected pesticides were alachlor, atrazine, cyanazine, metolachlor, and acetochlor. Concentration and fluxes of most pesticides in rain depicted a distinct seasonal pattern. The presence of agriculture pesticides in urban rain demonstrates that pesticides are being transported regionally through the atmosphere. The relatively consistent year-to-year flux of pesticides in Minneapolis indicates the regional background of pesticides in rain. The intensive row-crop agricultural area showed a significantly greater annual flux than the other four sampling sites that were in areas of either urbanization or less intensive agriculture.;A multi-year paired study of pesticides in rain and storm runoff in three watersheds in Minnesota was conducted to compare the mass loadings from two pathways to aquatic and terrestrial ecosystems. Seven other larger watersheds were selected from previous research to perform the same assessment. The mass contributed from the rain was 40 to 200 times greater than the riverine load in the urban watershed and equal to five times greater in the two agricultural watersheds in Minnesota. The magnitude of mass in rain is similar, if is not greater than, to that in runoff, over many orders of magnitude differences in the sizes of watersheds.