Bioavailability, biological activity and characterization of bound residues of diflubenzuron in wheat

Wheat grain was treated with radiolabeled diflubenzuron at 100 ppm and stored for various periods; up to 6 months. The grain was surface washed, Soxhlet-extracted with methanol, and the residues determined. A relative constant amount of bound residues (4%), i.e., non-extractable radioactivity, was found 4 months after application and remained constant. More than 97% of the extractable radioactivity in the grain after 6 months was identified as diflubenzuron. When the bound residues were fed to rats, 47% of the administered dose was eliminated via the urine and the remainder via feces within 96 h. Diflubenzuron was the major component in the urine. Adding bound residues to housefly media resulted in a dose-dependent mortality of housefly pupae. Bound residues were biologically active, preventing the emergence of adult houseflies. Supercritical fluid extraction of the bound residues extracted 92% and 96% of the radioactivity associated with grain and feces, respectively. Only diflubenzuron was present in these extracts. The bioavailability and biological activity of bound residues of diflubenzuron have been demonstrated and the identity of the radioactivity was shown to be parent compound. Based on these findings, bound pesticide residues can no longer be ignored or overlooked in the evaluation of pesticide residues and their possible toxicological implications.