Regressors of whole-carcass zinc phosphide/phosphine residues in voles: Indirect evidence of low hazards to predators/scavengers

Whole-carcass residues of the rodenticide zinc phosphide (Zn₃P₂) and hydrolyzed phosphine (PH₃) were determined for voles (Microtus spp.) that died following ingestion of a 2% Zn₃P₂ steam rolled oat (SRO) groats bait. Procedures involved: a three-day acceptance test to assess vole consumption (n=27) of control SRO groats and several one-day Zn₃P₂- (n=13) or control-bait (n=4) tests to characterize onset of pharmacotoxic signs and to obtain fatally-dosed carcasses for residue analyses. Carcasses were stored in liquid nitrogen (LN₂) to maximize retention of Zn₃P₂/PH₃ residues prior to chemical determinations. Linear regressions were computed between pairs of consumption and residue variables. Main results were the following: (1) mean (±SD) consumption of control bait was 2.5 (±0.9), 3.0 (±0.9), and 2.8 (±0.8) g on days 1, 2, and 3, respectively (10.6 ± 4.6% of body weight); (2) all test-bait voles (n=13) died 4–12 h after bait presentation, with lethargy and respiratory distress key signs of toxicosis; (3) whole-carcass Zn₃P₂ residues averaged 1.73 mg (minmax: 0.31–4.95), and PH₃ residues averaged 10.6 g (minmax: 0.5–21.0); and (4) significant linear regressions were found between bait consumption/Zn₃P₂ intake and body weight (r²=0.64, p0.001), carcass Zn₃P₂ and bait consumption/Zn₃P₂ intake (r²=0.32, p0.043), and carcass Zn₃P₂ and body weight (r²=0.60, p0.002). Certain analytical and hazards issues are discussed.