National Water-Quality Assessment (NAWQA) Program
Michael S. Majewski and Paul D. Capel, U.S. Geological Survey, Sacramento, California.
A comprehensive review of existing literature on the occurrence and distribution of pesticides in the atmosphere of the United States showed that the atmosphere is an important part of the hydrologic cycle that acts to distribute and deposit pesticides in areas far removed from their application sites. A compilation of existing data shows that pesticides have been detected in the atmosphere throughout the Nation, but most of the available information is from small-scale, short term studies, few of which lasted more than one year. Most of the pesticides analyzed for were detected in air, rain, fog, or show and include about 25 percent of the currently used pesticides. The geographical distribution of studies, and the type of sampling and analysis were highly variable with most of the historical study efforts concentrated in the Great Lakes area and California. Reported pesticide concentrations in air and rain were frequently positively correlated to their regional agricultural use. Most deviations from this relation could be explained by non- agricultural use of pesticides, sampling and analytical difficulties, or environmental persistence. High concentrations of locally used pesticides were found to occur seasonally, usually in conjunction with spring planting of row crops, but high concentrations also occurred during winter months in areas where dormant orchards were sprayed. The more persistent pesticides were detected at low concentrations throughout the year. Deposition of airborne pesticides can have significant effects on water quality, but neither the nature nor the magnitude of these effects can be determined on the basis of the type of data currently available. The lack of consistent, long term, regional and national monitoring and study of pesticides in atmospheric matrices severely limits assessment capability.