Mercury is a naturally occurring element that is toxic to humans and animals. It affects human nervous systems, particularly of young children and fetuses. At room temperature, mercury is a silvery, liquid metal, but it can also evaporate and become airborne like water. Mercury does not break down into less toxic substances.
Mercury used to be common in some products like switches, thermometers, and fluorescent lights. Those uses are less common now, but it’s still found in some products. When these items are broken or thrown away, mercury can escape into the environment. Activities such as burning coal and processing taconite also release mercury into the air.
Airborne mercury circulates in and out of the atmosphere, and may travel long distances before it falls to earth with precipitation or dust. Eventually this mercury ends up in lakes or oceans, where it can accumulate in fish.
One of the primary ways people are exposed to mercury is by eating contaminated fish. As fish eat plankton and smaller fish that are contaminated, mercury concentrations increase. Large fish that are popular in Minnesota, such as bass, walleye, and northern pike, tend to be the most contaminated. Many states, including Minnesota, have fish consumption advisories to inform people about how many meals of fish they can safely eat over a period of time. The EPA has concluded that most Americans are not at risk from mercury exposure. However, pregnant women, women who may become pregnant within the next several years, children under six, and people who consume unusually large quantities of freshwater sport fish, shark, or swordfish may be harmed by mercury. Excess mercury exposure before birth or in infancy can cause a child to be late in beginning to walk and talk and may cause lifelong learning problems.
Inhaling the vapor given off when mercury is heated is also dangerous, as is the mercury that becomes airborne if you break something like a mercury thermometer.
Mercury's effects can be very subtle. Excess mercury exposure in adults might cause trembling hands and numbness or tingling in lips, tongues, fingers or toes. These effects can begin long after the exposure occurred. At higher exposures, walking could be affected, as well as vision, speech, and hearing. In sufficient quantities, mercury exposure can be fatal.
Fish are the main source of food for many birds and other animals, and mercury can seriously damage the health of these species. Loons, eagles, otters, mink, kingfishers, and ospreys eat large quantities of fish. Because these predators rely on speed and coordination to obtain food, mercury may be particularly hazardous to these animals.
Research indicates that the following environmental effects are occurring:
- Minnesota loons are accumulating so much mercury that it may be affecting their ability to reproduce, (reported by K. L. Ensor, D. D. Helwig and L. C. Wemmer in "Mercury and Lead in Minnesota Common Loons," published by the MPCA Water Quality Division in 1992)
- Elevated levels of mercury have been found in Minnesota's mink and otters, (reported by K. L. Ensor, W. C. Pitt and D. D. Helwig in "Contaminants in Minnesota Wildlife 1989-1991," published by the MPCA Water Quality Division in 1993)
- Walleye reproduction may be impaired by the fish's exposure to mercury, (reported by J. G. Wiener and D. J. Spry in "Toxicological Significance of Mercury in Freshwater Fish," published by Lewis Publishers, Baca Raton, Fla., in 1996)
Frequently asked questions
Does mercury cause cancer?
The U.S. Environmental Protection Agency classifies mercury as a possible human carcinogen. So far, data are unsufficient to determine conclusively whether it causes cancer. However, it also appears that serious nerve damage would result from exposures to mercury much lower than the levels that might cause cancer.
How do scientists detect mercury poisoning?
Mercury poisoning can be detected through blood tests. Scientists also can detect exposures to mercury in the recent past by chemical analysis of human hair, because mercury is excreted from the body, in part, through the hair.
Do all scientists agree about the dangers of mercury?
While all scientists agree that mercury is toxic, they do not all agree on the amount of mercury that should be considered a human health hazard. Both the U.S. Environmental Protection Agency and the Minnesota Department of Health have calculated limits to mercury consumption using an approach that allows for human variability in how the body responds to mercury. This method is most likely to be over-protective rather than under-protective of human health.
What can you do?
- Conserve energy, which reduces the need for utilities to burn coal.
- Buy green power.
- Avoid buying products containing mercury. For example, look for non-mercury fever thermometers.
- Do not throw products that contain mercury in the trash. Take them to your county household hazardous waste facility.