U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

Pesticides in the Atmosphere of the Mississippi River Valley, Part I - Rain

By Michael S. Majewski, William T. Foreman, and Donald A. Goolsby

This report is available in pdf format: Majewski.pdf

ABSTRACT

Weekly composite rainfall samples were collected in three paired urban and agricultural regions of the midwestern United States and along the Mississippi River during April - September 1995. The paired sampling sites were located Mississippi, Iowa, and Minnesota. A background site, removed from dense urban and agriculture areas, is 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 3 of 3 related transformation products were detected in one or more sample from each paired site. The detection frequency of 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 (µg pesticide/m^² per season) occurred at the agricultural sites in Mississippi (1,980 µg/m^²) and Iowa (490 µg/m^²) and at the urban site in Iowa (696 µg/m^²). Herbicides accounted for the majority of the wet depositional loading at the Iowa and Minnesota sites, but methyl parathion (1,740 µg/m^²) was the dominant compound contributing to the total loading at the agricultural site in Mississippi. Atrazine, CIAT (a transformation product of atrazine) and dacthal were detected most frequently (76, 53, and 53 percent, respectively) at the background site indicating their propensity for long-range atmospheric transport.