1National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, Office of Research and Development, United States Environmental Protection Agency, Narragansett, RI, USA; 2Patuxent Wildlife Research Center, United States Geological Survey, Laurel, MD, USA; 3National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, Office of Research and Development, United States Environmental Protection Agency, Duluth, MN, USA; 4National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, Office of Research and Development, United States Environmental Protection Agency, Grosse Isle, MI, USA
Abstract
Methyl mercury in the aquatic food web poses significant health risks to both wildlife and humans.1 One primary source of mercury contamination for both the aquatic and terrestrial systems is atmospheric deposition of inorganic mercury from industrial emissions.2 Once in the environment, inorganic mercury is converted to methyl mercury that enters the food web and bioaccumulates in prey species. Top-level predators including piscivorous birds and humans are at greatest risk. Methyl mercury is the most toxic form of mercury, and is associated with behavioral changes, neurologic impairment, reproductive failure, and death. There is concern that methyl mercury may threaten populations of many wildlife species.
In this study the American kestrel was exposed to dietary methyl mercury in a controlled setting at the United States Geological Survey (USGS) Patuxent Wildlife Research Center (PWRC). The purpose of this pilot study was to determine sensitivity and pathologic change of this species to the toxicant and gather information about methyl mercury absorption and distribution. Results from this study will help (1) design a reproductive study and (2) develop a physiologically based toxicokinetic model of bioaccumulation of mercury in kestrels.
Though the concern for methyl mercury in avian species is primarily in piscivores, the American kestrel was chosen as the animal model for study because it can be kept and bred in captivity and is a top-level carnivore. Information from the kestrel studies will also provide needed information to better understand risk from methyl mercury to wild piscivorous birds.
Dosage of birds included control, 3, 6, and 12 ppm methyl mercury chloride (dry weight) mixed with Nebraska Brand Bird of Prey Diet (Central Nebraska Packing, Inc., North Platte, NE) for one, two, four, or eight weeks. Tissues examined histopathologically were kidney, liver, spinal cord, and brain.
Lesions were found only in the cerebellum of 12 ppm birds; all birds at this dose had similar lesions. Changes included neuronal degeneration, loss of myelin, and mild inflammation.
Acknowledgments
This project is a collaboration between the United States Environmental Protection Agency and the USGS.
Literature Cited
1. Heinz GH. Chapter 11. Mercury Poisoning in Wildlife. In: Fairbrother A, Locke LN, Hoff GL, eds. Noninfectious Diseases of Wildlife. Ames, IA: Iowa State University Press; 1996;118–127.
2. US EPA. Mercury Study Report to Congress. EPA-452/R-97-003. Washington, DC: Office of Air Quality Planning and Standards and Office of Research and Development. 1997.