ABSTRACT
Pesticides may enter surface waters directly through runoff, spills, or various effluents. Contamination also may be indirect, with pesticides first entering the atmosphere or ground water, and then transported to surface waters. The methods of application or routes of delivery of pesticides to each source, the important processes involved in transport of pesticides from each source to surface waters, and finally, the relative importance of each source of pesticides to surface waters are examined. Generally, the major source of most pesticides to surface waters is agricultural use. Agricultural use accounts for about 75 percent of total pesticide use in the United States. Pesticides generally move from fields to surface waters in runoff or in drainage induced by rain or irrigation. Pesticide use in forestry represents a significant portion of the total use of a number of pesticides, such as triclopyr, hexazinone, and diflubenzuron. The transformation of a pesticide results in changes in its chemical structure.
