ARS | Publication request: Sorption-Desorption Imidacloprid and Three Metabolites As a Function of Soil Depth

Submitted to: International Association Of Environmental And Analytical Chemistry
Publication Acceptance Date: May 19, 2004
Publication Date: August 16, 2004
Citation: Koskinen, W.C., Werdin, N.R., Cox, L., Norberg, K.A. 2004. International Association Of Environmental Analytical Chemistry Abstracts. International Association Of Environmental And Analytical Chemistry. P. 30.

Technical Abstract: Sorption-desorption is arguably the most important process affecting the transport of pesticides through soil since it controls the amount of pesticide available for transport. Sorption is usually characterized by determining batch sorption coefficients, which are then used in transport models to predict movement from the soil surface through the subsoils. Variability in subsurface soil properties can significantly affect prediction in pesticide transport. This research characterized the sorption-desorption of imidicloprid, and three of its metabolites, as a function of changing soil properties with depth in two soils. For instance, in samples from a sandy loam soil core, imidacloprid Koc values ranged from 181 L/kg in the surface 30 cm of soil to 512 L/kg for soil from the 700 cm depth, a 2.8-fold increase. If OC contents of the subsoils and the surface Koc value were used to predict subsurface Kf values, predicted subsurface Kf would be 30 to 80% of actual measured values. These data illustrate the importance of evaluation of the sorption data used to predict potential mobility; mobility could be either over- or under-predicted depending on sorption coefficients used. In this case, if Koc values of the surface soil were used to predict sorption (either Koc or Kf) on subsurface soils, sorption would be underestimated and predicted potential mobility would be overestimated. Also, not taking into account the hysteresis in desorption of imidicloprid from soil would overestimate the predicted potential mobility. Similar results were obtained for guanidine and urea metabolites of imidacloprid. Understanding the variability of soil properties and processes as a function of soil depth is necessary for accurate prediction of pesticide dissipation.