Tissue Distribution, Elimination, and Metabolism of O-Ethyl O-4-Nitrophenyl Phenylphosphonothioate in Hens Following Daily Dermal Doses

The absorption, distribution, elimination, and metabolism of the insecticide O-ethyl O-4-nitrophenyl phenylphosphonothionate (EPN) were studied in the hen. A daily dermal dose of 0.5 mg/kg (0.56 μCi/dose) of [14C]EPN (O-ethyl O-4-nitrophenyl [14C] phenylphosphonothioate) was applied for 10 consecutive days to hens. Three treated hens were killed at each of the following time intervals: 1,5,10, and 15 days after the administration of the last dose. A total of 65% of the cumulative dose was excreted in the combined urinary and fecal excrement 15 days after the last dose. Small amounts of radioactivity were deposited in the egg yolk (0.8%) and the egg albumen (0.3%). No 14C02 was detected in the expired air. Radioactivity in the tissues reached a peak of 12% of the total administered dose one day after the last dose; 14C decreased to 1.5% of the total dose (12% of the peak value) 15 days after the administration of the last. dose. The concentration of radioactivity was highest in the liver, followed by the kidney, gall bladder, bile, small intestine, ceca, large intestine, and skin. Relatively low concentrations of 14C were detected in the central and peripheral nervous tissues. O-Ethyl phenylphosphonic acid (EPPA) was identified as the major urinary-fecal metabolite followed by phenylphosphonic acid (PPA) and O-ethyl phenylphosphonothioic acid (EPPTA). EPN accounted for most of the radioactivity in tissues except in the liver. In this tissue most of the radioactivity was identified as EPPA, EPPTA, and PPA.