BIOAVAILABILITY, BIOLOGICAL-ACTIVITY AND CHARACTERIZATION OF BOUND RESIDUES OF FENVALERATE IN WHEAT

Wheat grain was treated with radiolabeled fenvalerate and stored for various periods; up to 6 months. The grain was surface washed, Soxhlet-extracted with methanol, and the residue determined. A relative constant amount of bound residues (6%), i.e. , nonextractable radioactivity, was found 2 months after application and remained constant. Seventy-eight percent of the extractable radioactivity in grain after 6 months was identified as fenvalerate. When bound residues were fed to rats, 40% of the administered dose was eliminated through the urine and the remainder through the feces within 90 h. Approximately a third of the radioactivity excreted in the urine and feces was intact fenvalerate. Feeding bound residues to fathead minnows at a subchronic dose resulted in a time-dependent mortality of 40% of the fish after 6 days exposure. Supercritical fluid extraction of the bound residues liberated 96% of the radioactivity, of which 75% was identified as fenvalerate and the remaining 25% as 3-phenoxybenzoic acid. The bioavailability and biological activity of bound residues of fenvalerate have been demonstrated and the identity of the radioactivity characterized. Based on these findings, bound residues can no longer be ignored. They must be included in the establishment of pesticide tolerances and in the evaluation of their toxicological hazards.