Use of Modeling in Developing Label Restrictions for Agricultural Chemicals

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Abstract
The movement and degradation of agricultural chemicals in soil and groundwater is a complex process, influenced by climatic conditions, site characteristics, chemical properties, and agricultural practices. Because of this complexity, mechanistic models are useful tools in evaluating environmental fate. Although currently available unsaturated zone models often do not provide accurate concentration profiles when compared with field measurements, they can be used to estimate the depth and extent of movement. Another application of modeling is to compare predicted movement under different simulation conditions to determine the significance of the various factors affecting the behavior of agricultural chemicals. When properly designed and interpreted, modeling studies can contribute to the understanding of the environmental fate of agricultural chemicals. When necessary, modeling can also be useful in developing management practices included on the label or in state regulations. Modeling has been a frequently used tool in developing restrictions for minimizing the movement of aldicarb residues into groundwater and preventing residues in drinking water. Examples of model use include optimizing application timing, estimating well setback distances, and identifying vulnerable soils.