Excretion and residues of the herbicides benzoylprop-ethyl flamprop-isopropyl and flamprop-methyl in cows,pigs and hens

Two wild oat herbicides, benzoylprop-ethyl and flamprop-methyl were administered to lactating cows at low dose levels (0.3–3.0 mg/kg in total diet) and the excretion of total metabolites in milk, urine and faeces was measured. Total residues in tissues were also determined. Similarly a third and related herbicide flamprop-isopropyl was fed to cows, pigs and hens (at 0.5 mg/kg in total diet) and the residues were determined in excreta and tissues, including eggs. The amounts of the compounds fed were equivalent to approximately 10–300 times the total residue found in cereal treated in the field. Residues in milk in most cases were well below 0.001 mg/kg; in muscle samples <0.003 mg/kg; and in eggs, 0.0008 mg/kg, decreasing by 50% in approximately 3 days to 0.0001 mg/kg 4 days after the termination of treatment. Elimination of the herbicides from the animals was rapid in every case and this, together with the low residue levels, was attributed to very efficient metabolic de-esterification to the parent carboxylic acid metabolites (benzoylprop and flamprop). These metabolites possess physical properties ideally suited for excretion via the kidneys and bile into urine and faeces and, conversely, unsuited for transport into milk and eggs.