Zinc phosphide residues in gray-tailed voles (Microtus canicaudus) fed fixed particles of a 2% grain bait

Abstract

This study measured depelted-carcass residues of zinc phosphide (Zn 3P 2, CAS ı1314-84-7) in 8 (4 and 4♀) gray-tailed voles ( Microtus canicaudus). Six (3 3♀) voles were confined individually in 1.89 dkl (5 gal) plastic pails that contained 5, 2% Zn 3P 2 steam-rolled-oat (SRO) groats; 2 voles (1 and 1♀) served as analytical (unbaited) controls. Four test voles (3 1♀) died within 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 carcasses were stored frozen and depelted carcasses were analyzed within 31 days for Zn 3P 2 residues using a acid-hydrolyzation, gas-chromatographic (GC) method. Analytical controls were euthanized, with carcasses stored and analyzed the same as test voles. A mean (±SD) 4.7 (±0.8) SRO groats were consumed by the test voles; this converted to a mean (±SD) intake of 2.15 (±0.38) mg Zn 3P 2 and dose of 73.25 mg⧹kg (±22.95) Zn 3P 2. The mean (±SD) Zn 3P 2 residue in the 6 test vole carcasses was 0.42 mg (±0.68); control carcasses contained <0.009 mg Zn 3P 2—<method limit of detection (MLOD). Results confirm that: (1) carcass residues of Zn 3P 2 in voles are variable, but typically <50% of ingested rodenticide and (2) risks of secondary poisoning posed by Zn 3P 2-baited voles to avian and mammalian predators⧹scavengers are low due to the relatively high toxic thresholds (>20 mg⧹kg) required to affect these species.