National Water-Quality Assessment (NAWQA) Project
What happens to the pesticides that are applied and how much enters the atmosphere? This is not a simple question to answer, and the environmental fate of pesticides is dependent on many factors, such as the physical and chemical properties of the pesticide; how, when, and where it was applied, and weather conditions. Recent studies have shown that many pesticides readily evaporate into the atmosphere. Evaporation is a continuous process that occurs over weeks, months, and years, until all of the pesticide molecules are degraded. Seventy-five percent or more of what is applied, depending on the pesticide, can ultimately be lost through evaporation.
Annual deposition of selected pesticides by rain has been calculated in several areas of the country. The amounts generally account for less than one percent of the total amounts applied. Although this seems like very little, it can represent many tons for some high use pesticides. In addition, rain and snow are not the only way pesticides are deposited to the earth's surface. Deposition of vapors and particles also occurs, but there is an inadequate understanding of these dry deposition processes.