Modeling and Predicting Pesticide Exposures

Models provide a means for representing a real system in an understandable way. Conceptual models help to identify the major influences on where a chemical is likely to be found in the environment, and as such, need to be developed to help target sources of data needed to assess an environmental problem. This chapter appraises the available models for predicting exposure to pesticide. In general, developing a model requires two main steps. First, a model of the domain and the processes being studied must be defined. Then, a model of the boundary conditions is especially needed to represent the environment surrounding the study domain. Research scientists often develop physical or dynamic models to estimate the location where a chemical would be expected to move under controlled conditions, only on a much smaller scale. Isolated systems are usually encountered only in highly controlled reactors, so are important in modeling pesticide formulation and manufacturing but are not directly pertinent to pesticide exposure modeling. Pesticide transport and fate models can be statistical (stochastic) and/or deterministic. Statistical models include the pollutant dispersion models, such as the Lagrangian models, which follow the movement of a control volume starting from the source to the receptor locations. Deterministic models are used when the physical, chemical, and other processes are sufficiently understood so as to be incorporated to reflect the movement and fate of chemicals. More comprehensive models provide realistic descriptions of the underlying processes and are invaluable for performing detailed analysis. Thus, the evolution of models will allow for more realistic scenarios, especially regarding personal exposures to pesticides.