Mercury Contamination Over Environment
Watersheds tend to concentrate mercury through erosion of mineral deposits and atmospheric deposition. Plants absorb mercury when wet but may emit it in dry air. Plant and sedimentary deposits in coal contain various levels of mercury. Like plants, mushrooms can also accumulate mercury from the soil.
Human activities, like the application of agricultural fertilizers and industrial wastewater disposal, are examples of how humans release mercury directly into the soil or water. The mercury that is released in the environment ends up in surface water or soils eventually. When the pH values in acidic surface waters are between five and seven, the mercury concentrations in the water will increase. This is due to the mobilization of mercury in the ground near a water source.
Most compounds containing mercury are poisonous.The major contaminant found in fish is mercury. This element occurs naturally in trace amounts in the environment. But industrial pollution can produce mercury that accumulates in lakes, rivers and oceans. Microorganisms in the water convert the mercury to a highly toxic form, called methyl mercury.
Methylmercury is an organic form of mercury that has been used to preserve seed grain. Methylmercury can also be produced from metallic mercury or mercury compounds in bodies of water by the action of bacteria. Outbreaks of methylmercury poisoning have occurred following ingestion of treated seed grain, meat from animals fed treated seedgrain, or fish from waters contaminated with methylmercury, such as Minamata Bay in Japan.
Fetuses and young infants are very sensitive to methylmercury's effects. Methylmercury causes central nervous system (brain and spinal cord) damage and the severity of the damage depends on the extent of the exposure. Many of the CNS effects of mercury poisoning are similar to those seen in cerebral palsy , and methylmercury is thought to cause a form of cerebral palsy.
As good as fish are for your health, be aware of potential downsides. Some types of fish may contain significant amounts of contaminants, such as mercury, polychlorinated biphenyls, dioxins or other chemical pollutants. Fish acquire these toxins from pollutants in lakes, rivers and oceans.
In January 2001, the FDA issued a warning that pregnant women, women who may become pregnant, nursing mothers, and small infants to avoid fish that may contain unsafe levels of methylmercury. These fish include large, longer-lived fish, such as swordfish, king mackerel, shark, or tilefish. The FDA especially warns against noncommercial fish, or fish caught by friends and family, and the agency recommends that consumers check their local or state health departments for warnings against locally caught, noncommercial fish.
Recently,the nation's largest gold-producing state is being asked to investigate whether mercury emissions from its mines are contaminating area fisheries.
Citing a recent study by the University of Nevada, Reno, a coalition of environmentalists, health care advocates, sportsmen and American Indians said that a fish consumption advisory for mercury should be issued for one large reservoir in northeast Nevada and perhaps other fisheries downwind from mining operations.
Fish tissue samples collected by university researchers at Wild Horse Reservoir showed mercury concentrations that the U.S. Environmental Protection Agency considers a public health risk, especially to children and pregnant women, the groups said.
"We believe that an investigation into the public health risks from fish consumption from reservoirs, lakes and rivers in northern Nevada is warranted," they said in a letter to the state health administrator. "It is important that Nevada families and visiting tourists have accurate information to determine which fish are safe to eat and how many fish are safe to eat."
State Health Administrator Alex Harts will ask the state's health officer, Dr. Branford Lee, to examine the study and the groups' request, spokeswoman Martha Farmstead said.
There are about two dozen major gold mines in Nevada. They produced 6.85 million ounces of gold in 2005 with a value of about $3.05 billion — third in the world behind South Africa and Australia.
The coalition said the EPA's Toxic Release Inventory showed Nevada's mercury emissions totaled more than 4,605 pounds of mercury released in 2004 — more than 95 percent of it from gold mines in northern Nevada.
The Nevada mines are responsible for one-fourth of all U.S. mercury air emissions west of Texas, according to the Great Basin Mine Watch, a nonprofit environmental watchdog group based in Reno.
Scientists have reported high mercury levels in fish and waterfowl in Idaho and Utah downwind of the Nevada mines, the groups said.
"Yet very little monitoring has been done to determine the extent of mercury contamination in fish and waterfowl in northern Nevada," they said.
Great Basin Mine Watch has criticized new state regulations adopted last year because they don't include a cap on mercury emissions.
Dante Piston, spokesman for Nevada's environmental protection agency, said the state is implementing "aggressive, comprehensive" new rules, which are the first of their kind in the nation.
"Both the mining and power plant regulations go beyond what the federal government and other states have enacted," he said. "Once the regulations are fully implemented, mercury emissions will be highly controlled."
Ruses Fields, president of the Nevada Mining Association, said the gold mines are working with the state and the EPA to adopt the new controls.
Most of the mines operate on federal lands, many of which the Western Shoshone tribe claims as its own.
"These companies are operating in this manner without our consent. They need to stop and be honest about the hazards they are creating in our communities," said Arson Bill of the Western Shoshone Defense Project.
Large, predatory fish — such as tilefish, swordfish and king mackerel — tend to have higher levels of methyl mercury than do smaller fish because they're higher in the aquatic food chain. Small fish eat organisms that contain methyl mercury, and this contaminant is then stored in their bodies. Larger fish eat the smaller fish, gaining higher concentrations of the toxin. The longer a fish lives, the larger it grows and the more mercury it can collect.
If you consume fish that contains methyl mercury, the toxin can accumulate in your body as well. It can take weeks, months or even a year for your body to remove these toxins.The FDA and the Environmental Protection Agency (EPA) report that for most people, however, the amount of mercury they consume by eating fish isn't a health concern.