Aldicarb ground water study

As the study moves into the second phase when field data will be collected for analysis after application of the pesticide aldicarb, background data will continue to be collected to better define and characterize the local ground-water system and its relation to the unsaturated zone. 

As stated earlier, the means by which to test a model are dependent on the biases of the model tester and the purposes of his exercise. The purpose of the calibration in this study is to set up the exposure assessment simulations, which will determine the potential for aldicarb to contaminate the ground water in the scenarios modeled. As will be seen shortly, this potential is represented by model results at a point deep in the unsaturated zone. As such, it becomes Imperative to accurately portray aldicarb fate in the unsaturated zone. Since these field studies showed that high concentrations of aldicarb were maintained near the soil surface, parameters were adjusted to portray that behavior. If anything, this exercise has uncovered a discrepancy between model theory and reality, and a future direction in PRZM development and/or field testing might be to test the theories proposed. Nonetheless, the calibration in this study is valid since the purpose is to duplicate reality, given the limitations of the model. 

The following example using aldicarb illustrates how to derive an ADI. Aldicarb is a pesticide that has been detected in ground water in Florida and elsewhere. The EPA is currently in the process of establishing a drinking water criterion for aldicarb. Weil and Carpenter (19) studied the effects of aldicarb sulfoxide on rats and determined a NOEL of 0.125 mg/kg/day. This is supported by another rat study by Mirrow et al. (20), which resulted in a NOEL equal to 0.12 mg/kg/day. An ADI is estimated for aldicarb, using the NOEL from the Weil and Carpenter study and an uncertainty factor of 100 ... 

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