More on Mercury

  • TUNA TYPES- One particularly common source of low-level mercury exposure is tuna. Because they are large, long-lived predators, tuna accumulate more mercury in their tissue than smaller, short-lived fish. When tested for mercury – in parts per million, flesh from albacore tuna, which take five years to mature, was shown to contain about four times as much mercury as chunk light tuna, which is harvested from younger fish.
  • HISTORY– Mercury was known to the ancient Chinese and Hindus; the element has been found in Egyptian tombs from 1500 B.C.
  • SOURCE– Mercury rarely occurs free in nature but can be found in ores, principally cinnabar. The element, which exists in its natural form as a mix of seven stable isotopes, is most often found near volcanoes or geothermal springs. The metal is obtained by heating cinnabar in an air current and condensing the vapor.
  • USES– Mercury easily forms alloys, called amalgams, with other metals like gold, silver, and tin. The element has many uses in the chemical industry, such as in the manufacture of sodium hydroxide and chlorine by the electrolysis of brine, as well as in making advertising signs, mercury switches, and other electrical apparatuses. It is also used to make sensitive measuring devices for laboratories. Other uses are in dental work, batteries, and catalysts. Because of mercury’s toxicity, many of these uses are under review.
  • FAVORED FISH- An inspector at a California cannery in 1953 spot-checks canned tuna. In the United States, canned tuna is the third most commonly purchased food item, after sugar and coffee, based on dollar sales per amount of shelf space devoted to the product. An EPA study reported the median amount of mercury, measured in parts per million, in the following varieties of canned tuna: chunk light: .08 parts per million; canned albacore tuna: .34ppm; fresh or frozen tuna: .30ppm. A 2004 EPA advisory mentions five types of fish and shellfish that are low in mercury: shrimp, canned light tuna, salmon, pollack, and catfish. The advisory also warns consumers not to eat shark, swordfish, king mackerel, and tilefish because they all contain high levels of mercury.
  • MERCURY FILLINGS- Dental amalgams, known as silver fillings, are composed of roughly 50 percent mercury. Studies of people with mercury-containing dental fillings show a correlation between the number and size of the fillings and the amount of mercury excreted in their urine. The relationship suggests that the mercury is derived from mercury vapor released from the fillings. Some evidence shows that the level of mercury in the brain tissue of fetuses, newborns, and young children is also directly proportional to the number of surfaces of amalgam fillings the mother has.
  • TESTING TROUBLE- Chronic low-level exposure to mercury is difficult to quantify because analyses of blood, urine, and hair will reflect only recent acute exposure, not past exposure. If acute mercury poisoning is diagnosed, administering compounds that bind to mercury and draw it out of the tissue — a process called chelation therapy — can remove elemental or inorganic mercury. However, chelation cannot remove methylmercury. Mercury has a strong affinity for the brain, especially the fetal brain. Methylmercury has been shown to alter the construction of structural components of the brain called microtubules and influence the development of neurons.
  • SOURCES OF MERCURY RELEASE- During the last 150 years, human activities may have doubled or tripled natural amounts of mercury in the atmosphere. Although there are many natural sources of mercury emissions — such as volcanoes, geothermal springs, geologic deposits, and the ocean — there are also numerous industrial sources such as coal combustion, waste incineration, and mining. The greatest contributors are coal-fired utilities and industrial boilers, which account for about 50 percent of the transmission of inorganic mercury to the atmosphere.
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