Pesticides in the Hydrologic System

More than 600 million pounds of pesticides are used each year in the United States to control many different types of weeds, insects, and other pests in a wide variety of agricultural and urban settings. National use of herbicides and insecticides on cropland and pasture has grown from 190 million pounds of active ingredient in 1964, to an estimated 630 million pounds in 1988. Though increased use has resulted in increased crop production and other benefits, concerns about the potential adverse effects of pesticides on the environment and human health have grown steadily.

Figure 1. Pathways of pesticide movement in the hydrologic cycle. Importance of the Atmosphere

In many respects, the greatest potential for adverse effects of pesticides is through contamination of the hydrologic system, which supports not only human life, but aquatic life and related food chains as well. Water is one of the primary means by which pesticides are transported from their application areas to other parts of the environment. Thus, there is potential for movement of pesticides into and through all components of the hydrologic cycle (see Figure 1).