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 (> or = 10.6 +/- 4.6% of body weight); (2) all test-bait voles (n = 13) died approximately 4-12 h after bait presentation, with lethargy and respiratory distress key signs of toxicosis; (3) whole-carcass Zn3P2 residues averaged 1.73 mg (min-max: 0.31-4.95), and PH3 residues averaged 10.6 micrograms (min-max: 0.5-21.0); and (4) significant linear regressions were found between bait consumption/Zn3P2 intake and body weight (r2 = 0.64, p < or = 0.001), carcass Zn3P2 and bait consumption/Zn3P2 intake (r2 = 0.32, p < or = 0.043), and carcass Zn3P2 and body weight (r2 = 0.60, p < or = 0.002). Certain analytical and hazards issues are discussed.