Factors affecting pesticide occurrence and transport in a large Midwestern river basin

Several factors affect the occurrence and transport of pesticides in surface waters of the 29,400 km2 White River Basin in Indiana. A relationship was found between pesticide use and the average annual concentration of that pesticide in the White River, although this relationship varies for different classes of pesticides. About one percent of the mass applied of each of the commonly used agricultural herbicides was transported from the basin via the White River. Peak pesticide concentrations were typically highest in late spring or early summer and were associated with periods of runoff following application. Concentrations of diazinon were higher in an urban basin than in two agricultural basins, corresponding to the common use of this insecticide on lawns and gardens in urban areas. Concentrations of atrazine, a corn herbicide widely used in the White River Basin, were higher in an agricultural basin with permeable, well-drained soils, than in an agricultural basin with less permeable, more poorly drained soils. Although use of butylate and cyanazine was comparable in the White River Basin between 1992 and 1994, concentrations in the White River of butylate, which is incorporated into soil, were substantially less than for cyanazine, which is typically applied to the soil surface.