RELATIONS BETWEEN PESTICIDE USE AND RIVERINE FLUX IN THE MISSISSIPPI RIVER BASIN

In an intensive subcontinental study of pesticides in surface waters o f the United States, concentrations of 26 high-use pesticides were mea sured at nine sites in the Mississippi River basin from May 1991 throu gh March 1992. Calculated total fluxes were combined with agricultural -use data to estimate the percentage of applied pesticide reaching the mouths of the Mississippi River and six major tributaries. For most p esticides, the riverine flux was less than 2% of the mass applied agri culturally. The fluxes were only marginally related to runoff-potentia l ratings based solely on the pesticides' chemical and environmental p roperties. The insecticide diazinon was detected frequently in rivers draining the three basins with the highest population densities, appar ently as a result of urban use.