Metabolism of monocrotophos in animals

Regarding the metabolic fate of monocrotophos, it appears that the mechanisms summarized below are largely independent of the animal species. Furthermore, significant sex dependency of any of these parameters has not been found. ABSORPTION: After oral administration to rats and goats, monocrotophos is rapidly and almost completely absorbed from the intestinal tract. There is convincing evidence that monocrotophos is readily absorbed after dermal administration to man, pigs, and rabbits.

Monocrotophos and/or its metabolites are evenly distributed between the tissues and organs of the animals; usually, the highest concentrations are typically found in organs involved in the elimination process, i.e., liver and kidney. There are no indications for any organ-specific retention. In assessing the relevance of tissue residues, the fact that monocrotophos may contribute to the carbon pool and may thus, via de novo synthesis of endogenous compounds, lead to nonmonocrotophos-related 14C-residues needs to be considered.

The biotransformation of monocrotophos is well understood. Three different metabolic reactions are involved in the initial biotransformation: N-demethylation, O-demethylation, and cleavage of the vinyl phosphate bond. The compound is completely degradable, ultimately leading to CO2. All carbon atoms of the molecule have the potential to enter the carbon pool. EXCRETION: After absorption and biotransformation, monocrotophos and/or its metabolites are rapidly eliminated from the animals. Excretion is predominantly in the urine, typically 70-90% of the dose, and usually less than 10% is voided with the feces. Significant amounts, i.e., 6% of the crotonamide backbone, is expired as CO2 by rats. In lactating goats, approximately 2% of the dose is eliminated with the milk. Due to the water solubility of monocrotophos, some portion of the dose may escape biotransformation and consequently be excreted unchanged.