Mathematical model of the uptake of non-ionized pesticides by edible root of root crops

Abstract

A plant uptake model was developed to estimate the residual amount of non-ionized pesticides in the edible roots of root crops. An examination of the route of uptake of furametpyr (log Kow=2.36) and pyriproxyfen (log Kow=5.37) suggested that the more lipophilic of the two pesticides, pyriproxyfen, was mainly adsorbed by the root peel and incorporated by diffusion into the root core. On the other hand, the less lipophilic pesticide, furametpyr, was mainly taken up via the transpiration stream into the core through the root hairs. Based on the results, a mathematical model for the uptake of a pesticide into edible roots was developed based on the following route; (1) incorporation into the root core via the transpiration stream through the root hairs, (2) adsorption by the root peel, and (3) diffusion from the peel to the root core. To test the model, residual amounts of furametpyr and pyriproxyfen were analyzed and compared to those predicted when the pesticides were treated at one-tenth of the concentration in the model construction. Ratios of predicted to measured residual concentrations were 1.01-1.38 and 0.75-1.28 for furametpyr and pyriproxyfen, respectively, showing the effectiveness of the model as a predictive tool.