Metabolism of and residues associated with dermal and intramuscular application of radiolabeled fenthion to dairy cows.

Abstract

P32-labeled fenthion having a specific activity of 5.0 mc per g was formulated as a 0.5% emulsion and applied dermally to 2 dairy cows at a rate of 1 quart per cow. Two other lactating cows were treated intramuscularly with 3.5 g of fenthion (8.6 mc per g) per cow. Fenthion and certain oxidative metabolites were isolated from milk, urine, and feces following either method of treatment. The ratio of these metabolites in the urine was vastly different from that in the feces. Fenthion was rapidly degraded to phosphoric acid derivatives and was eliminated primarily in the urine and to a lesser extent in the feces. Residues were negligible in edible tissues 14 days after dermal treatment, but persisted throughout the 21-day test period in cows treated intramuscularly. Mortality of the house fly, Musca domestica L., and the stable fly, Stomoxys calcitrans (L.). caged on cows treated dermally with fenthion was 100% at 1 day after treatment.