Measuring degradation of zinc phosphide residues in possum stomach contents.

Zinc phosphide (ZnP) has been identified as a potentially cost-effective vertebrate pesticide for possum (Trichosurus vulpecula) control in New Zealand. We established methodology for analysis of microencapsulated ZnP formulations (MZP) and investigated the half-life of residual ZnP in the stomach contents of poisoned possums. An interlaboratory study was conducted to compare results of ZnP analysis in stomach contents. The half-life of ZnP was 3.4 days for ZnP in possum stomach contents and 6.7 days in vomit. Subsequent estimates were made of 34 and 67 days, respectively, for residual ZnP to decline to concentrations below the 1 microg/g method detection limit.