Residues of Phosvel in plasma and in adipose tissue of hens after single oral administration

Abstract In the first study, hens (24 months old) were sacrificed at various time intervals after a single oral dose of 50 or 250 mg/kg of Phosvel (leptophos), O -(4-bromo-2,5-dichlorophenyl)- O -methylphenylphosphonothioate. At both doses, the Phosvel concentration in plasma reached a maximum within 3 hr and then declined rapidly; after 72 hr no residues were detectable. The concentration of Phosvel in fat attained a peak after 12 hr in both groups and was closely related to dose. The elimination of Phosvel from the fat was very slow. In the second study, younger (6 months old) and older (21 months old) hens were given a single oral dose of 250 mg/kg of the pesticide and were sacrificed after 1, 3, 7, 14, 21, and 28 days. Phosvel was detected in the fat of one of the older birds 28 days after treatment. The mean values of Phosvel in fat decayed logarithmically and biological half-life was 1.5 days for the younger birds and 4.9 days for the older birds.