ZINC PHOSPHIDE RESIDUES IN GRAY-TAILED VOLES (MICROTUS-CANICAUDUS) FED FIXED PARTICLES OF A 2-PERCENT GRAIN BAIT

This study measured depelted-carcass residues of zinc phosphide (Zn3P2 . CAS # 1314-84-7) in 8 (4 male and 4 female) gray-tailed voles (Micro tus canicaudus). Six (3 male 3 female) voles were confined individuall y in 1.89 dkl (5 gal) plastic pails that contained 5, 2% Zn3P2 steam-r olled-oat (SRO) greats; 2 voles (1 male and 1 female) served as analyt ical (unbaited) controls. Four test voles (3 male 1 female) died withi n 7.5 h after bait exposure: whereas, 2 test voles showed no signs of toxicosis and were euthanized 7.0 h after bait exposure. Whole carcass es were stored frozen and depelted carcasses were analyzed within 31 d ays for Zn3P2 residues using a acid-hydrolyzation, gas-chromatographic (GC) method. Analytical controls were euthanized, with carcasses stor ed and analyzed the same as test voles. A mean (+/- SD) 4.7 (+/- 0.8) SRO greats were consumed by the test voles; this converted to a mean ( +/-SD) intake of 2.15 (+/- 0.38) mg Zn3P2 and dose of 73.25 mg/kg (+/- 22.95) Zn3P2. The mean (+/- SD) Zn3P2 residue in the 6 test vole carca sses was 0.42 mg (+/- 0.68); control carcasses contained < 0.009 mg Zn 3P2- < method limit of detection (MLOD). Results confirm that: (1) car cass residues of Zn3P2 in voles are variable, but typically <50% of in gested rodenticide and (2) risks of secondary poisoning posed by Zn3P2 -baited voles to avian and mammalian predators/scavengers are low due to the relatively high toxic thresholds (> 20 mg/kg) required to affec t these species. Published by Elsevier Science Ltd.