Bioavailability and biological activity of wheat‐bound chlorpyrifos‐methyl residues in rats

Wheat grain was treated with 14C‐chlorpyrifos‐methyl to generate bound residues for determining their bioavailability to rats. In a parallel experiment, bound residues were prepared with non‐labelled chlorpyrifos‐methyl to determine possible adverse effects in rats fed the grain‐bound residue for 28 and 90 days. Two dose levels of 10 and 50 ppm were initially used on the grain. The 10 ppm led to the formation of 25.1% bound residues’ (2.51 ppm) after 6 months as determined by radiomeasurement. The higher dose was assumed to form 12.55 ppm bound residues. When 14C‐bound residues were fed to male rats for 24 hours, the animals eliminated 75% of the radioactivity in urine, 7% in expired air and 8% in faeces after 3 days, indicating that the bound residues were highly bioavailable. A further “bioavailable” amount (4%) was found in selected organs. In toxicity tests in rats bound residues were found to provoke biological effects such as inhibition of plasma ChE activity. The SGPT activity was elevated in females at both dose levels suggesting a hepatotoxic potential. Hematological data showed increases in hemoglobin concentration in males at both dose levels and RBC count in both sexes at both dose levels. The results strongly suggest that wheat‐bound chlorpyrifos‐methyl residues can cause adverse biological effects in the rat.