Mercury and the Environment Bio Sci 2B
Mercury: The Element Liquid at room temperature Atomic #: 80 Atomic Mass: g “Quicksilver” Density: 13.6 g/mL
The Different Forms of Mercury Exists in different forms: elemental, inorganic, and organic mercury Mercury alloys easily with other metals such as gold, silver, and tin (amalgams). Important mercury salts include HgCl2, Hg2Cl2, Hg(ONC)2, and HgS (vermillion). Metallic mercury is used in thermometers, barometers, and fluorescent light bulbs.
How Mercury Enters the Environment Mercury can enter the environment through human activities such as coal burning and product manufacturing. Mercury can also enter the environment from natural sources such as volcanoes. Globally, 4800 – 8300 tons of mercury are deposited per year due to both natural and human generated causes.
Bioaccumulation of Mercury Bioaccumulation of mercury begins when bacteria in soils convert the mercury to methylmercury, a highly toxic form. The concentrations of methylmercury in large fish can be over a million-fold larger than in the surrounding water. The methylmercury is concentrated further up the food chain.
Overview of Mercury Health Effects Almost all people have at least trace amounts of mercury in their tissues. People may be exposed to mercury in any of its forms under different situations. The effects of mercury exposure can be very severe, subtle, or may not occur at all. Because young children and unborn fetuses are still developing, they are particularly sensitive to the effects of methylmercury on the nervous system.
Methylmercury Effects & Exposure Organic mercury, such as methyl mercury is more toxic than inorganic mercury. Symptoms of methylmercury poisoning may include: impairment of the peripheral vision, disturbances in sensations, lack of coordination of movements, impairment of speech, hearing, walking, and muscle weakness. Methylmercury exposure in the womb, which can result from a mother's consumption of fish and shellfish that contain methylmercury, can adversely affect a baby's growing brain and nervous system. Impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methylmercury in the womb.
Statistics and Details The reference dose the EPA uses is 0.1 µg/kg body weight/day as an exposure without recognized adverse effects. This is equivalent to about 5.8 µg/L of whole blood. The EPA estimated that 7% of women of childbearing age would have blood mercury concentrations greater than those equivalent to the reference dose (1997). It is estimated that more than 300,000 newborns each year may have increased risk of learning disabilities associated with in utero exposure to methylmercury.
Effects of Other Mercury Compounds Elemental (metallic) mercury primarily causes health effects when it is breathed as a vapor where it can be absorbed through the lungs. With large acute exposures to metallic mercury vapor, the lungs may be permanently damaged. High exposures to inorganic mercury may result in damage to the gastrointestinal tract, and the nervous system. Long term exposure to inorganic mercury affects the kidneys and can cause tubular necrosis. Organic mercury compounds are more readily absorbed via ingestion than inorganic mercury compounds.
Reducing Mercury Exposure Fish consumption advisories in 44 states have limited or eliminated the fishing of certain highly mercury contaminated fish. The FDA maximum permissible level is 1 part of methyl mercury in a million parts of seafood (1ppm). On March 15 th, the EPA issued the Clean Air Mercury Rule to reduce mercury emissions from coal-fired power plants. This rule will hopefully reduce emissions by 33 tons, nearly 70% when fully implemented. Medical waste incinerators, which emitted about 50 tons of mercury per year into the air in 1990, have gone down 95% since the EPA issued emission standards for these medical waste incinerators in 1997.
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