Mercury Poisoning Causes, Symptoms, and Prevention on MedicineNet.com

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Mercury Poisoning

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Mercury introduction

Mercury is contained in some of the fish we eat, whether caught in local lakes and streams or bought in a grocery store. Mercury is also contained in some of the products we use, which may be found in your home, at the dentist, and at schools. This article provides links to information about sources of mercury exposure, potential health effects, fish that may contain mercury, consumer products that contain mercury, and ways to reduce your exposure to mercury.

General information about mercury and mercury exposure

Forms of mercury. Mercury is a naturally occurring element that is found in air, water and soil. It exists in several forms:

elemental or metallic mercury,
inorganic mercury compounds, and
organic mercury compounds.

Sources of mercury. Mercury is an element in the earth's crust. Humans cannot create or destroy mercury. Pure mercury is a liquid metal, sometimes referred to as quicksilver that volatizes readily. It has traditionally been used to make products like thermometers, switches, and some light bulbs.

Mercury is found in many rocks including coal. When coal is burned, mercury is released into the environment. Coal-burning power plants are the largest human-caused source of mercury emissions to the air in the United States, accounting for over 40 percent of all domestic human-caused mercury emissions. EPA has estimated that about one quarter of U.S. emissions from coal-burning power plants are deposited within the contiguous U.S. and the remainder enters the global cycle. Burning hazardous wastes, producing chlorine, breaking mercury products, and spilling mercury, as well as the improper treatment and disposal of products or wastes containing mercury, can also release it into the environment. Current estimates are that less than half of all mercury deposition within the U.S. comes from U.S. sources.

Exposure to mercury. Mercury in the air eventually settles into water or onto land where it can be washed into water. Once deposited, certain microorganisms can change it into methylmercury, a highly toxic form that builds up in fish, shellfish and animals that eat fish. Fish and shellfish are the main sources of methylmercury exposure to humans. Methylmercury builds up more in some types of fish and shellfish than others. The levels of methylmercury in fish and shellfish depend on what they eat, how long they live and how high they are in the food chain.

EPA works with the U.S. Food and Drug Administration (FDA) and with states and tribes to issue advice to women who may become pregnant, pregnant women, nursing mothers, and parents of young children about how often they should eat certain types of commercially-caught fish and shellfish. Fish advisories are also issued for men, women, and children of all ages when appropriate. In addition, EPA releases an annual summary of information on locally-issued fish advisories and safe-eating guidelines to the public. Fish is a beneficial part of the diet, so EPA & FDA encourage people to continue to eat fish that are low in methylmercury.

Another less common exposure to mercury that can be a concern is breathing mercury vapor. These exposures can occur when elemental mercury or products that contain elemental mercury break and release mercury to the air, particularly in warm or poorly-ventilated indoor spaces.

Health effects of mercury. Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages. Research shows that most people's fish consumption does not cause a health concern. However, it has been demonstrated that high levels of methylmercury in the bloodstream of unborn babies and young children may harm the developing nervous system, making the child less able to think and learn. More information

Ecological effects of mercury. Birds and mammals that eat fish are more exposed to mercury than other animals in water ecosystems. Similarly, predators that eat fish-eating animals may be highly exposed. At high levels of exposure, methylmercury's harmful effects on these animals include death, reduced reproduction, slower growth and development, and abnormal behavior.

Reducing mercury releases. EPA issues regulations that require industry to reduce mercury releases to air and water and to properly treat and dispose of mercury wastes. EPA also works with industry to promote voluntary reductions in mercury use and releases, and with partners in state, local and tribal governments to improve their mercury reduction programs. EPA works with international organizations to prevent the release of mercury in other countries. The public can contribute to mercury reduction efforts by purchasing mercury-free products and correctly disposing of products that contain mercury by reducing demand for products whose production leads to the release of mercury into the environment.