Mercury in Their Midst

When released into the environment in substantial amounts over a period of time, mercury is a well-documented killer, not only of wildlife but of people as well.

The raw element itself, still called quicksilver by some, is the only common metal found in nature that’s liquid at ordinary temperatures. Humans have found hundreds of uses for it, from making medicines to the manufacture of other products ranging from pesticides to paints, thermometers to hats. The phrase “mad as a hatter” comes from centuries past, when mercury was used in the manufacture of felt hats. A common byproduct was mentally and physically impaired workers, hapless victims of acute mercury poisoning.

Mercury’s pathway into Everglades wildlife primarily begins in the skies, with mercury-loaded rainfall. Sulfate-reducing bacteria, mainly living in sediments and in mats of floating algae, absorb rainwater mercury and turn it into its organic form, methylmercury (CH₃Hg⁺). Microorganisms which eat such bacteria feed successive populations of larger organisms in the food web. At each step, methylmercury levels get concentrated. For wetland-dependent animals such as wading birds, raccoons and some panthers, concentrations can reach dangerously high levels. (BRUCE HALL ILLUSTRATION)

Like most elements, mercury is something of a chameleon, able to assume many forms. In the environment, the most toxic form is methylmercury, a tasteless, colorless and odorless compound that readily enters the food chain. Once in the tissues of organisms, methylmercury has a strong tendency to stay put. Over time, the compound can build up to dangerous levels in fish, shellfish and other aquatic life. People and wildlife with heavy diets of such tainted foods can accumulate the poison as well and suffer crippling, even lethal consequences.

In the digestive tract, methylmercury gets rapidly absorbed and can invade all tissues, including the brain and the wombs of pregnant women. In high enough concentrations, the neurotoxin can cause irreversable brain and nerve damage, seizures, kidney failure, even blindness.

Of all the abuses of mercury by manufacturers this century, by far the worst occurred in Japan, in the vicinity of a small fishing village on the island of Kyushu. Between 1953 and 1960, the Chisso Chemical Company dumped mercury-loaded sludge into Minimata Bay, where it accumulated in fish and shellfish. The pollution killed fish, seabirds, housecats--and reportedly as many as 700 inhabitants of the bayshore village. Hundreds more were crippled, including scores of babies born with horrific birth defects.

Nothing so terrible has happened in the U.S., although there have been numerous instances of methylmercury poisoning. The first example to draw significant public attention was in 1969, when some children in New Mexico got sick from eating hog meat from animals fed mercury-treated feed grain.

As it happens, indigenous peoples tend to eat lots of fish, which too often puts them at risk for mercury poisoning. Miners in Brazil use tons of mercury each year in a process for gleaning gold dust from rivers near Manaus. In the early 1990s, health officials found downstream forest peoples with methylmercury in their systems at levels up to four times a World Health Organization safety standard.

In 1983, Pomo Indians in California had to stop eating so many local fish because of high mercury in the fillets. Two bands of Indians in Ontario, Canada were awarded an $18.6 million settlement in a 1986 lawsuit against a paper mill that had poisoned a river that gave the Indians their livelihood. Mercury-loaded fish from the river sickened dozens of tribe members, and resulted in the birth of several infants with severe mental and physical defects.

Chippewa Indians in Wisconsin in 1990 were found to have blood levels of mercury high enough to cause developmental problems in fetuses. The Chippewas had a fondness for the walleye that swam in local lakes.

In Florida, Miccosukees and Seminoles are obliged to deal with a mercury contamination problem that defies belief. Their tribal lands are virtually synonymous with much of the Everglades, one of the largest tracts of unsullied wilderness left in the world--with one exception. Although statistics aren’t clear on the point, the Everglades may have the highest levels of mercury contamination ever seen in a freshwater ecosystem, period.

Most Everglades fish, turtles, alligators, wading birds, raccoons and even some insects carry mercury burdens way above normal. The average concentration of methylmercury in a fillet of an Everglades largemouth bass is 1.5 parts per million (ppm), three times what the state’s Department of Health calls safe.

To many Everglades Indians, the mercury problem is just one more insult to their environment they must deal with, says Joe Quetone, director of the Gov. Lawton Chiles’ Council on Indian Affairs. The tribes already are battling exotic species of fish and other wildlife, saltwater intrusion and pollution from agribusiness. “They’ve just added mercury to the list,” Quetone said.

Still, some tribal leaders are fully resentful of how the ‘Glades mercury issue has been handled by state authorities and have balked at what they call being “singled out” by health officials for mercury testing. So far, no evidence has surfaced that indicates a health problem tied to mercury among any of the Everglades’ human inhabitants.

But that may be because many Indians don’t eat fish anymore, said one Miccosukee woman living in Big Cypress. “Nobody eats these fish around here,” she said. “When we want fish, we do like everybody else--we go to Publix.” --F.S.

Reposted with permission of Frank Stephenson, editor of FSU Research in Review. 6/8/98