Excretion and residues of the pyrethroid insecticide cypermethrin in lactating cows

Abstract

Abstract Two radiolabelled forms of racemic [ 14 C]cypermethrin ( 14 C at the benzylic carbon or at C‐1 of the cyclopropane ring) were separately administered twice daily to lactating cows in portions of the feed. The amounts dosed were equivalent to 0.2, 5 and 10 μg of cypermethrin per g of feed. The radioactivity eliminated in the milk indicated that the ingestion and elimination of radioactivity were in balance at about day 4 after the start of dosing. Urine and faeces were equally the major routes of elimination, and only a fraction of a percent of the dose appeared in the milk. The residue in the milk was unchanged cypermethrin and was found at a concentration that was proportional to the dose. At the high cypermethrin intake of 10 μg g −1 of diet, the residue in the milk was 0.03 μg g −1 . Concentrations of residues in the tissues, measured after 7, 20 or 21 days of treatment, were low and in the order: liver>kidney>renal fat>subcutaneous fat>blood>muscle>brain. The major residue in the liver and kidney of a cow that received 10 μg of cypermethrin per g of diet was N ‐(3‐phenoxybenzoyl)glutamic acid. Other conjugates of 3‐phenoxybenzoic acid and of 3‐(4‐hydroxyphenoxy)benzoic acid (unidentified, with the exception of the glycine conjugate) were also present. The residue in fat (about 0.1 μg g −1 from an intake of 10 μg g −1 of feed) consisted mainly of cypermethrin.