Pesticides in the atmosphere of the Mississippi River Valley, part I - rain

Weekly composite rainfall samples were collected in three paired urban and agricultural regions of the Midwestern United States and along the Mississi ppi River during April-September 1995. The paired sampling sites were locat ed in Mississippi, Iowa, and Minnesota. A background site, removed from den se urban and agriculture areas, was located near Lake Superior in Michigan. Herbicides were the predominant type of pesticide detected at every site. Each sample was analyzed for 47 compounds and 23 of 26 herbicides, 13 of 18 insecticides, and three of three related transformation products were dete cted in one or more sample from each paired site. The detection frequency o f herbicides and insecticides were nearly equivalent at the paired Iowa and Minnesota sites. In Mississippi, herbicides were detected more frequently at the agricultural site and insecticides were detected more frequently at. the urban site. The highest total wet depositional amounts (mu g pesticide /m(2) per season) occurred at the agricultural sites in Mississippi (1980 m u g/m(2)) and Iowa (490 mu g/m(2)) and at the urban site in Iowa (696 mu g/ m(2)). Herbicides accounted for the majority of the wet depositional loadin g at the Iowa and Minnesota sites, but methyl parathion (1740 mu g/m(2)) wa s the dominant compound contributing to the total loading at the agricultur al site in Mississippi. Atrazine, CIAT (a transformation product of atrazin e and propazine) and dacthal were detected most frequently (76, 53, and 53% , respectively) at the background site indicating their propensity for long -range atmospheric transport. (C) 2000 Elsevier Science B.V. All rights res erved.