The Dangers of Mercury 6/2010
What threat does mercury pose?
Mercury has long been known to be a deadly poison in high doses. Methylmercury is the organic form that is the most toxic. Children of women exposed to relatively high levels of methylmercury during pregnancy show delayed onset of walking and talking, reduced neurological test scores, and delays and deficits in learning ability, according to U.S. Environmental Protection Agency reports. EPA officials also say there is growing evidence that methylmercury exposure can have adverse cardiovascular effects for adults, resulting in elevated blood pressure and incidence of heart attack.
Mercury in the air-
Mercury is released into the atmosphere by many industrial processes, especially coal-fire power plants and mines. Most of the mercury pollution is elemental mercury, which is not as toxic. But it mixes in the atmosphere with other chemicals and is transformed through oxidation and other biological processes after it is deposited over the land into the more lethal methylmercury. It then washes into waterways at widely varying rates. In rivers and lakes, it moves up the food chain to concentrate at high levels in the flesh of fish.
Mercury in the water-
Methylmercury in the water and sediment is taken up by plankton. Minnows and juvenile fish eat large quantities of plankton over time. Larger predatory fish consume many smaller fish, accumulating methylmercury in their tissues. The older and larger the fish, the greater the potential for high mercury levels in their bodies. Fish are caught and eaten by humans, causing methylmercury to accumulate in human tissues. Since mercury is tightly bound to proteins in all fish tissue, including muscle, there is no method of cooking or cleaning them that will reduce the amount of mercury in a meal. From the 1950s to the 1970s, several mass poisonings took place in Japan and in Canada involving methylmercury from consumption of fish from contaminated waters. In the United States, the number of states that have issued health advisories limiting consumption of fish has risen steadily from 27 states in 1993 to 41 states in 1999.
How much mercury is safe?
In 1996, the EPA set its guideline for methylmercury in the diet at 0.1 micrograms of mercury per kilogram of body weight per day. A 1994 EPA survey found an average of 0.26 parts per million of mercury (ppm) in freshwater fish nationwide. Ocean fish have average mercury levels of 0.21 ppm.
An average person weighing 132 pounds can eat 6 micrograms of mercury per day without exceeding the EPA recommended dose. If each gram of fish contains 0.2 micrograms of mercury, an average person could only eat 30 grams of fish per day without exceeding the EPA dose. The walleye sampled in Salmon Falls Creek Reservoir had .55 ppm of mercury. So the average person who ate one meal a week from Salmon Falls would exceed EPA's recommended dose.
How can I learn more about the dangers of mercury?
Contact the Idaho Division of Environmental Quality in Boise at 208-373-0502, or go online to: http://www.deq.state.id.us .
For EPA information on mercury and fish advisories, go online to: http://www.epa.gov/
Read about the Mercury Policy Project. Online, go to: www.mercurypolicy.org/