A Nonlinear Dynamic Simulation Model for Xenobiotic Transport and Whole Plant Allocation Following Foliar Application. II. Model Validation

A validation study was performed for a nonlinear computer simulation model describing xenobiotic absorption, whole plant allocation, and metabolism. Validation involved comparisons of predicted xenobiotic behavior with actual data (from independent studies in the literature) for the herbicides bentazon, chlorimuronethyl, prosulfuron, rimsulfuron, thifensulfuron, clopyralid, picloram, fluroxypyr, imazaquin, imazethapyr, acifluorfen, 2,4-D, 2,4-DB, dicamba, haloxyfop-methyl, sethoxydim, and pyridate. Simulations were performed with parameters describing the plant, the herbicide physicochemical properties, and the environmental conditions used in the experimental studies. The conformity between simulated and actual absorption, whole plant distribution, and metabolism data were evaluated by the ratio of simulated values to actual values in 25 species treated with 18 herbicides from several chemical families such as benzothiadiazole, pyridinecarboxylic acid, imidazolinone, diphenyl ether, phenoxyalkanoic acid, benzoic acid, aryloxyphenoxypropionate, cyclohexanedione, and phenylpyridazine. In general, most predicted values for herbicide absorption, whole plant allocation, and metabolism were close to actual values for this group of herbicides. Comparisons between model prediction and actual herbicide absorption showed that in 79% of comparisons the ratios of predicted/[served were between 0.8 and 1.2. For whole plant allocation, 61% of the comparisons showed a ratio of 1 ± 0.3. These results demonstrate the utility of this new computer simulation model in predicting xenobiotic behavior in plants and the potential use of such models in rational design of herbicide molecules for optimal plant uptake and whole plant allocation.