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

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Abstract
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 μg (minmax: 0.5–21.0); and (4) significant linear regressions were found between bait consumption/Zn3P2 intake and body weight (r2=0.64, p≦0.001), carcass Zn3P2 and bait consumption/Zn3P2 intake (r2=0.32, p≦0.043), and carcass Zn3P2 and body weight (r2=0.60, p≦0.002). Certain analytical and hazards issues are discussed.