Effects of Dietary Methylmercury Exposure on American Kestrels

Objective/Intended Use

The purpose of this research project is to advance the science behind ecological risk assessment of environmental releases of mercury (methylmercury) to avian wildlife. This project will involve collection of data on the pharmacokinetics and toxicological effects of dietary exposures to methylmercury on the American kestrel (Falco sparverius), a small falcon found throughout the U. S. This work supports the research objectives identified in the Agency's Mercury Research Strategy, which calls for research to improve the understanding of methylmercury toxicological effects on avian species.

Abstract

Several recent ecological risk assessments and criteria development efforts suggest that sensitive individuals of some piscivorous (fish eating) wildlife populations may be experiencing adverse effects from methylmercury exposure. The primary exposure route of methylmercury to these species is through the consumption of contaminated fish and other aquatic life. Despite the growing body of knowledge on the risks of methylmercury exposure to avian and other ecological receptors, corroborating field data on population-level effects from such exposures are generally lacking or are severely limited. Furthermore, substantial uncertainty underlies the aforementioned methylmercury ecological risk assessments which undermines the usefulness of the results. For example, available data on the effects of methylmercury on actual wildlife species of concern (e.g., eagle, kingfisher, osprey, mink, otter) is extremely limited in part because of difficulties in conducting controlled studies on such species. As a result, toxicological effects data must be extrapolated from commonly tested and distantly related species (e.g., mallard, chicken, pheasant). This interspecies extrapolation involves significant uncertainty because species sensitivity can exceed an order of magnitude. The goal of this project is to reduce uncertainty in interspecies extrapolations of toxicological effects of methylmercury through the collection of appropriate toxicological and pharmacokinetic data on the American kestrel. The kestrel was chosen as a study organisms because of its taxonomic similarity to other raptors of concern (e.g., osprey, eagle) and because it is one of the few raptors where successful colonies have been established in the laboratory. The dose-residue-response relationship between methylmercury exposure and host of reproductive, developmental, behavioral immunotoxicological and histopathological endpoints on adults and young will be quantified. In addition to the toxicological data, year two of this study will involve collecting necessary pharmacokinetic data to develop and test a physiologically-based toxicokinetic (PB-TK) model. The intent of this model would be to aid in extrapolation of methylmercury toxicity to other species. * A pilot study to determine the dosing regime and address experimental design issues was completed in FY00. In FY01 and FY02, the toxicological study was conducted, but was terminated early due to experimental problems. Much (but not all) of the information on the methylmercury toxicokinetics was obtained during these FY01 and FY02 studies. In FY03, additional toxicokinetic data were collected. In FY04, the toxicological dose-residue-response portion of the study was successfully conducted. Data analysis and preparation of manuscripts are proceeding in FY05 and FY06. Draft manuscripts summarizing the effects of methylmercury on kestrel reproduction and toxicokinetics have been prepared and are expected to be submitted for publication by the end of 2006 or early 2007.

Project Status

A pilot study to determine the dosing regime and address experimental design issues was completed in FY00. In FY01 and FY02, the toxicological study was conducted, but was terminiated early due to experimental problems. Much (but not all) of the information on the methylmercury pharmacokinetics was obtained during these FY01 and FY02 studies. In FY03, additional toxicokinetic and immunotoxicological data will be collected. In FY04, the toxicological dose-residue-response portion of the study will be conducted with the development of the PB-TK model.

Project Start Date

10/01/2000