Graduate Thesis Or Dissertation

Improving ecological risk assessment of pesticides for nontarget terrestrial vertebrates

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  • The Quotient Method (QM) is used by the United States Environmental Protection Agency (USEPA) in ecological risk assessments of pesticides for nontarget organisms. The QM requires several assumptions regarding exposure and hazards of pesticides to wildlife; several of these assumptions have not been tested. During 1997-99, I conducted three experiments using the gray-tailed vole (Microtus canicaudus) as a model species to test three assumptions of the QM. The experiments were conducted in 24 0.2-ha fenced vole-proof enclosures. In Experiment 1, I tracked voles using radio-telemetry and found that animals did not move from contaminated to uncontaminated habitat to avoid exposure to a pesticide, thus supporting one assumption of the QM. In Experiment 2, I studied demographic responses of gray-tailed voles and northern bobwhite quail (Colinus virginianus) to liquid and granular formulations of diazinon. The results of Experiment 2 indicated that quail were more susceptible to granular diazinon than to liquid diazinon because of direct consumption of diazinon granules. Neither formulation of diazinon at 0.55 or 1.55 kg AI/ha adversely affected vole demography. In Experiment 3, I used sprinklers to simulate a 0.25-cm rainfall to test the assumption that the expected environmental concentration (EEC) of a pesticide is estimated immediately after application, and that rainfall does not modify the risk of pesticides to animals. The 0.25-cm rainfall may have reduced the risk of voles to Guthion® 2S either by improving the dry season habitat or by washing more pesticide residues down to the soil and reducing exposure of the animals. This experiment did not support the assumption of the QM that weather would not affect the EEC of pesticides. Last, I used a Ricker model incorporating demographic stochasticity to simulate the 1998 and 1999 vole populations and a single pesticide application at different population sizes. The simulations demonstrate that demographic stochasticity could cause uncertainties in predictions of significant effects of pesticide on voles, especially for small populations. These simulations suggest that ecological risk assessments of pesticides to nontarget wildlife should consider demographic characteristics of wildlife species to minimize the uncertainty of predictions.
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