Summary of aldicarb monitoring and research programs in the U.S.A.

Abstract

Since 1979, over 130,000 soil and water samples have been collected and analyzed for aldicarb in monitoring and research programs conducted in the U.S.A. Comprehensive field research studies have been conducted on 40 plots located in 14 states and involving eight different crops. In addition, exploratory studies have been conducted in eight states including three in which field studies were not conducted at a later date. Drinking water samples have been collected in 39 states. Many laboratory studies have been performed to better define degradation mechanisms and rates. Modeling simulations have been performed to interpret field data and to properly apply the results to other situations. The movement and degradation of aldicarb residues in the unsaturated and saturated zone in a complex process affected by soil and hydrogeological properties, climatic conditions, and agricultural practices. These studies show that in most areas aldicarb residues degrade in the upper portion of the unsaturated zone. In the few areas where aldicarb residues reach groundwater, the combined effects of the primarily lateral movement of groundwater and the continuing degradation usually constrain aldicarb residues to shallow groundwater neat treated fields. Most of the cases where aldicarb residues in drinking water have occurred in excess of the EPA (and WHO) health advisory level of 10 μg L −1 (a MCL of 7 μg L −1 is being proposed by the EPA) resulted from applications made at planting to potatoes. Generally, these instances of drinking water residues have been in the Northeast and Wisconsin: however, above guideline residues in drinking water wells have occurred as result of applications to lily bulbs in northern coastal California, sugar beets in Wyoming and citrus in central Florida. Management practices have been implemented to eliminate the occurrence of aldicarb residues in drinking water wells from future applications. These management practices have consisted of changes in application timing, application rates, and restrictions on applications near shallow drinking water wells in areas with vulnerable soils and shallow water tables. Almost all of the residues in drinking water wells currently exceeding guidelines are the result of applications made prior to the adoption of these management practices.