() Risk assessment model for predators and scavengers exposed indirectly to a rodenticide.

Giddings, J1, Warren-Hicks, W2, Mortensen, S3, Edwards, P4, Hosmer, A3, 1 Parametrix, Inc., Rochester, MA, USA2 The Cadmus Group, Inc., Chapel Hill, NC, USA3 Syngenta Crop Protection, Greensboro, NC, USA4 Syngenta Crop Protection, Jealotts Hill, Bracknell, Berks, UK

ABSTRACT- A probabilistic model is described for estimating the risk to predators and scavengers from indirect exposure to a rodenticide. The model combines predictions of dietary exposure with information about toxicological effects to estimate the likelihood that an individual predator or scavenger will accumulate a lethal dose. The exposure model is a probabilistic implementation of a standard dietary dose model based on food ingestion rate, percentage rodents in the diet, percentage of rodents that have been exposed to a rodenticide baiting program, and concentration of rodenticide in exposed rodents. Data on some of the model parameters (especially dietary composition and rodenticide concentrations in rodents) are available from field studies, while other parameters are based on expert opinion or assumptions. The model generates exposure probability curves for individuals, and also simulates variability among individuals. Effects of rodenticide exposure are estimated from laboratory studies with birds and mammals. A Bayesian hierarchical approach combines raw data from all studies into calculated dose-response relationships for individual species, or for species of unknown sensitivity. The exposure probability curves and dose-response curves are integrated into curves depicting the likelihood of lethal poisoning of an individual predator or scavenger. The model is illustrated using the coyote (Canis latrans) as the focal species. Through selection of distributions or assumptions for model parameters, the model can be used to explore a range of exposure scenarios and rodenticide baiting practices.

Key words: wildlife, rodenticide, probabilistic risk assessment, coyote

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