In March 2005, the U.S. Environmental Protection Agency (EPA) issued new regulations dealing with one of the world's most sinister contaminants: mercury. Toxic to both wildlife and humans, mercury is particularly dangerous for babies and children.

Once released into the environment, mercury concentrates in the food chain. Not only is it found in the air and water, but in plants and animals, as well. It is very adept at concentrating in aquatic plants and animals. Animals at the top of the food chain, including humans, are particularly susceptible to concentrations. And there is no easy way to rid the body of this poisonous metal.

Mercury in relatively small concentrations can damage brain cells and the nervous systems of some fragile animals. Human adults may be affected by high concentrations. None, however, are more susceptible to mercury's detrimental affects than babies and fetuses. According to reports, one out of every six women in the United States has high enough mercury levels to endanger her fetus.

According to the EPA, advisories against frequent consumption of some varieties of fish are found in some watersheds in nearly every state. Nineteen of the northern states from Washington to New England, and particularly in the Midwest, have issued advisories for all lakes or rivers or both.

Mercury is a silver-colored metal and is one of the 114 chemical elements. As the only metal to liquefy at room temperature, it flows easily and is sometimes called quicksilver. As an industrial product, mercury is used in various instruments, including thermometers, fluorescent lamps and batteries.

One of the principal industrial sources of industrial mercury is deposits of cinnabar, found in large amounts in Spain, Chile, Peru, the Philippines, Russia, Turkey and the United States. The largest U.S. deposits are in Alaska, California and Nevada. When mercury is used for industrial purposes, it is generally not released into the environment in large amounts during manufacture. When the manufactured products age, are abandoned or destroyed, however, there is a likelihood of the mercury escaping into the environment.

However, there are other sources of mercury found in some sedimentary rocks. Coal, in particular, may contain small amounts of mercury. When coal is burned, as in a coal-fired power plant, some of the mercury exits in its elemental form as droplets or attached to particles. Other mercury is oxidized during combustion and may be released into the atmosphere as a gas.

Elemental mercury tends to be heavy enough to fall out of the atmosphere within a relatively short time, especially with precipitation. Gaseous mercury, on the other hand, may remain airborne for weeks, months or years, encircling the earth with the wind patterns. These characteristics create conditions where no place on earth is free of this toxic element, but the geography of environmental mercury concentrations is particularly troublesome.

Coal-fired electrical plants in the United States generate about half of all mercury emissions. Power plants are more concentrated in the eastern half of the country. While much of the West has lower concentrations of mercury, the East and Northeast are extremely contaminated because the westerly winds drop mercury produced in power plants in the Midwest and Southeast.

There is no highly efficient technology currently capable of removing all mercury from power plant smokestacks. One solution to environmental mercury emissions proposed by the Bush administration is to "trade pollution credits." The strategy involves heavily polluting plants literally "buying the excess clean rights" from low polluting plants.

Although proponents say that the cost of the credit purchases will cause polluters to reduce emissions, it is easy to see that it does little to change the geographic pattern of mercury concentrations. Places directly downwind of a coal-fired plant are still going to find the greatest mercury concentrations. And generally regions with high numbers of smokestacks or downwind from large numbers of coal-fired generators are going to experience high mercury emissions and concentrations.

Some foods containing the highest concentrations of mercury include tuna, mackerel, swordfish, shark and other near-shore game fish. This doesn't mean that we shouldn't eat fish, but that we should do so in moderation. Other contaminated foods, including mothers' milk, aren't so easily avoided.

Mercury contamination is an issue already adversely affecting the health of 8 percent, or 81 million, of the world's 6.5 billion people