Sorption and bound residue formation of linuron, methylparathion, and metolachlor by carrot tissues: Kinetics by on-line HPLC microextraction

The feasibility of determining the identities and kinetics behavior of three pesticides in carrot tissue slurries using a novel on-line HPLC microextraction was investigated. Linuron, methylparathion, and metolachlor were added to aqueous slurries of carrot tissue particles smaller than 150 mu m. For each pesticide, the solution phase and the total pesticide recoverable from the whole slurry concentrations were separately monitored over a 10 day period. Kinetics curves for three categories of chemical species including solution phase pesticides, labile sorbed fractions, and unrecovered fractions were obtained. The linuron and metolachlor data are consistent with the commonly reported two-step sorption mechanism consisting of labile sorption followed by intraparticle diffusion, but the methylparathion data resemble a combination of labile surface sorption and solution phase and/or surface chemical decomposition. It is concluded that laboratory test methods of this type could be developed for assessing the risk of bound residue formation in vegetables.