Unsaturated zone aldicarb studies

Jones, R.E., Hansen, J.L., Romine, R.R., and Marquardt, T.E. Unsaturated zone studies of the degradation and movement of aldicarb and aldoxycarb residues, Environ. Toxicol Chem., 5 361-372, 1986. 

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. 

Research conducted on the movement and degradation of aldicarb residues in the unsaturated and saturated zones has shown that it is a complex process affected by soil and hydrogeological properties, climatic conditions, and agricultural practices. This paper presents the results of unsaturated and saturated zone field studies conducted in 16 states over a period of six years in which approximately 20,000 soil and water samples have been collected. Results from laboratory degradation studies are also included. 

Hornsby, A. G., P.S. C. Rao, W., B. Wheeler, P. Hkedi-Kizza, R. L. Jones, Fate of Aldicarb in Florida Citrus Soils 1. Field and Laboratory Studies, presented at Characterization and Monitoring of the Vadose (Unsaturated) Zone, Las Vegas, December 8-10, 1983. 

Jones, R. L., J. L. Hansen, R. R. Romine, T. E. Marquardt, "Unsaturated Zone Studies on the Degradation and Movement of Aldicarb and Aldoxycarb Residues." Submitted for publication, 1985. 

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. 

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