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Mercury and Other Environmental Contaminants
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. Mercury chemical symbolAn 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).
Research Question
We are part of the same environment as the Florida panthers. What effects are mercury and other environmental contaminants known to have on human health and reproduction?
In 1989 a joint monitoring project by the Florida Fish and Wildlife Conservation Commission, the Florida Department of Health and Rehabilitative Services, and the research questionFlorida Department of Environmental Regulation (now Environmental Protection) also found high levels of mercury in fish from the Everglades. 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 find out more about hormone disrupting chemicalsongoing 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).
Hormone-Disrupting Chemicals
Studies of wildlife, laboratory animals, and human populations indicate that a variety of man-made chemicals may negatively affect health and reproduction by mimicking, blocking, or in other ways disrupting natural hormones (Miller 1999).They may result in thyroid disorders as well as cryptorchidism, abnormally small penises, and low testosterone levels (Miller 1999). Exposure of developing rat fetuses to the herbicide nitrofen has been linked to cardiac septal defects (Lau et al. 1986 cited in Sileo et al. 1997).
University of Florida zoologist Louis Guillette has found male alligators in Lake Apopka in central Florida to have low levels of testosterone and penises 25 percent smaller than normal males. Females had elevated levels of estrogen, and eggs from Lake Apopka were three times as likely to die before hatching as eggs from other Florida lakes. Guillette attributes these defects to a spill from a chemical waste pond that sent large amounts of the pesticides including DDT into the lake (Guillette et al. 1994, 1996).
Chemicals known or suspected of being hormone disrupters include dioxins (byproducts of incineration of chlorine-containing compounds), PCBs (polychlorinated biphenels, substances used in various industrial processes), some pesticides, chemicals in some plastics, and lead and mercury (Miller 1999).
Many of these substances are biomagnified (increased in concentration) through the food chain and pose the greatest risk to humans, panthers, and other animals at the top of the food chain. Initial results of a study of hormone disrupting chemicals and Florida panthers found no abnormal hormone levels in a sample of adult male panthers (Sileo et al. 1997). Further research, however, is needed before conclusions can be made concerning the occurrence of these chemicals in panthers and their relationship to health and reproduction (Sileo et al. 1997).
Research on these chemicals and their effects is in its infancy. In 1996 the National Academy of Sciences embarked on an evaluation of hormone disrupters and their effects, and the U.S. Environmental Protection Agency has made hormone-disrupting chemicals a top research priority.
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.