In 1989 scientists first became aware of the potential threat of mercury to panthers in south Florida when a female panther from Everglades National Park died. An immediate cause of death could not be determined, although the panther did have severe parasite infestations, a uterine infection, and a healing fracture of her right front leg. Later tests revealed her liver contained high levels of mercury (110 parts per million). Her tissue also contained high levels of PCBs (polychlorinated biphenels) and pesticide residues. Death from mercury toxicosis (poisoning) has been reported in feral domestic cats in Japan with liver concentrations of 37-145 parts per million (Takeuchi et al. 1977, cited in Dunbar 1994).

    In 1989 a joint monitoring project by the Florida Game and Fresh Water Fish Commission, the Florida Department of Health and Rehabilitative Services, and the Florida Department of Environmental Regulation (now Environmental Protection) also found high levels of mercury in fish from the Everglades (see map). By 1996, 1 million acres of the Everglades drainage system was found to contain largemouth bass with over 1.5 ppm mercury, three times the level the Florida Department of Health considers safe for human consumption. The State Health Officer has advised against eating fish from the Everglades.

    Air pollution from metals mining and smelting, coal-fired utilities and industry, and solid waste incinerators are thought to be the major source of mercury contamination (Stephenson 1997). Some of this pollution may come from utilities and industries within Florida, but some may come from as far away as Europe. An ongoing study suggests that mercury from industry in the northeastern United States travels along with air currents east across the Atlantic where it mixes with air currents from the coast of Europe. These currents may carry pollution from Europe and even China. The air mass then travels south where the trade winds carry it back across the Atlantic to Florida. Summer thunderstorms then scour the mercury out of the upper atmosphere (Stephenson 1997).

    Raccoons are thought to be the major source of mercury in Florida panthers (Roelke and Glass 1992; Dunbar 1994). In the 15 months before her death, the panther with high levels of mercury in her liver fed only on small prey, primarily raccoons (Dunbar 1994). Mercury concentrations in panther tissues are lowest north of I-75 where adequate deer and hogs are available and are highest in the Everglades and southern Big Cypress where consumption of raccoons is highest (Roelke and Glass 1992; Dunbar 1994).

    Florida panthers are also exposed through the food chain to a variety of pesticides and other compounds with potential harmful effects on health and reproduction.

Probable Path of Mercury to the Florida Panther
	Mercury in rainfall is transformed to methyl mercury by bacteria in sediments and algal mats. Zooplankton feed on algae, and fish and crayfish consume zooplankton. Raccoons eat fish and crayfish, and panthers eat raccoons.

  
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