Mercury poisoning

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Mercury poisoning
Classifications and external resources
Elemental mercury
ICD-10 T56.1
ICD-9 985.0
DiseasesDB 8057
MedlinePlus 002476
eMedicine emerg/813 

Mercury poisoning, also known as mercuralism, is the phenomenon of toxication by contact with mercury.

The main dangers associated with elemental mercury are that at standard conditions for temperature and pressure, mercury tends to oxidize forming mercury(II) oxide, and that if dropped or disturbed, mercury will form microscopic drops, increasing its surface area dramatically.

Air saturated with mercury vapor at room temperature is at a concentration many times the toxic level, despite the high boiling point (the danger is increased at higher temperatures).

Watersheds tend to concentrate mercury through erosion of mineral deposits and atmospheric deposition. Plants absorb mercury when wet but may emit it in dry air. Plant and sedimentary deposits in coal contain various levels of mercury. Like plants, mushrooms can also accumulate mercury from the soil.

Human activities, like the application of agricultural fertilizers and industrial wastewater disposal, are examples of how humans release mercury directly into the soil or water. The mercury that is released in the environment ends up in surface water or soils eventually. When the pH values in acidic surface waters are between five and seven, the mercury concentrations in the water will increase. This is due to the mobilization of mercury in the ground near a water source.

Microorganisms are able to convert the mercury that reaches the surface water to methyl mercury and most organisms absorb this substance quickly. Methyl mercury is also known to cause nerve damage. Fish are among the organisms that absorb methyl mercury in great amounts from water. As a consequence, methyl mercury accumulates in fish and passes into the food chain. The deleterious effects of mercury consumed by animals that eat fish include reproductive failure, damage to intestines, stomach disruption, DNA alteration, and kidney damage.

Contents

[edit] Toxicity in human beings

Pure elemental mercury is a cumulative heavy-metal poison that is moderately absorbed through the skin, rather poorly absorbed through the gastrointestinal tract, and readily absorbed as vapor through the lungs. The element is strongly toxic when absorbed as vapor from the respiratory tract, but it is considerably less so when exposure occurs via other routes. Elemental mercury often passes through the GI tract without being absorbed, and historically mercury has occasionally been used for mechanical relief of intestinal obstructions (today the known toxicity of mercury has put an end to this practice).

Compounds of mercury tend to be much more toxic than the element itself, and organic compounds of mercury are often extremely toxic. Dimethylmercury, for example, is a potent neurotoxin that is lethal in amounts of a fraction of a millilitre.

Mercury damages the central nervous system, endocrine system, kidneys, and other organs, and adversely affects the mouth, gums, and teeth. Exposure over long periods of time or heavy exposure to mercury vapor can result in brain damage and ultimately death. Mercury and its compounds are particularly toxic to fetuses and infants. Women who have been exposed to mercury in pregnancy have sometimes given birth to children with serious birth defects (see Minamata disease).

Some of the toxic effects of mercury are reversible, either through specific therapy or through natural elimination of the metal after exposure has been discontinued. However, heavy or prolonged exposure can do irreversible damage, particularly in fetuses, infants, and young children. Exposure to certainly highly toxic compounds of mercury such as dimethylmercury can be fatal within hours or less.

Mercury exposure in very young children can have severe neurological consequences, preventing nerve sheaths from forming properly. Research has been done that demonstrates the inhibitory effect that mercury has on myelin, the building block protein that forms these sheaths.[1]

Mercury poisoning in the young is suspected as a possible cause of autistic behaviors. (see Generation Rescue)

Humans or animals poisoned with mercury or its compounds often manifest excessive salivation, a condition called mercurial ptyalism.

[edit] Thimerosal

Thimerosal, a preservative that contains mercury, has been added in very minute amounts to vaccines to prevent their deterioration since the 1930s. No adverse effects of thimerosal have ever been proved. However, organizations such as the American Academy of Pediatrics have recommended that the use of thimerosal be reduced as a precautionary measure. Today, with the exception of some flu vaccines, none of the vaccines used in the United States to protect preschool children against twelve infectious diseases contain thimerosal as a preservative.[2]

[edit] Dental amalgam

In recent years, some concern has arisen about the potential toxicity of mercury amalgam in dental restorative procedures (i.e., in tooth fillings). While it has been demonstrated that small amounts of mercury are released from fillings over time, it has not been conclusively proven that these releases are harmful (or harmless). The potential toxicity of amalgam is still a matter of considerable debate.

[edit] Occurrences of mercury poisoning

  • Another case of widespread mercury poisoning occurred in rural Iraq in 1971-1972, when grain treated with a methylmercury-based fungicide was used by the rural population to make bread. It had been intended as seed stock for planting.
  • China's first emperor, Qin Shi Huang Di, was driven insane and killed by mercury pills intended to give him eternal life.

[edit] Toxicity of mercury compounds

Elemental, liquid mercury is slightly toxic, while its vapor, compounds and salts are highly toxic and have been implicated as causing brain and liver damage when ingested, inhaled or contacted.

  • The most dangerous mercury compound, dimethylmercury, is so toxic that even a few microliters spilled on the skin, or even a latex glove, can cause death. One of the chief targets of the toxin is the enzyme pyruvate dehydrogenase (PDH). The enzyme is irreversibly inhibited by several mercury compounds, the lipoic acid component of the multienzyme complex binds mercury compounds tightly (mercury binds to the sulfur atoms in lipoic acid) and thus inhibits PDH.
  • Through bioaccumulation, methylmercury in the environment works its way up the food chain, reaching high concentrations among populations of some species such as tuna. Mercury poisoning in humans will result from persistent consumption of tainted foodstuffs. Larger species of fish, such as tuna or swordfish, are usually of greater concern than smaller species, since the mercury accumulates up the food chain. The largest incidence of methylmercury poisoning occurred in Minamata, Japan. Minamata disease caused the deaths of over 1000 people and the disabling of many more. The U.S. Food and Drug Administration (FDA) advises women of child-bearing age and children to completely avoid swordfish, shark, king mackerel and tilefish and to limit consumption of king crab, snow crab, albacore tuna and tuna steaks to 6 oz. or less per week. However, there is no evidence that moderate consumption of fish in the U.S. poses a significant health hazard. One recent Harvard Medical School study of mothers and their infants suggests that the nutritional benefits of eating fish outweighs the potential drawbacks of methylmercury.[5] In the HMS study, each additional weekly serving of fish consumed by the mother during pregnancy was associated with an increase in infant cognition.
  • Ethylmercury is a breakdown product of the antibacteriological agent thimerosal which has effects similar but not identical to methylmercury.
  • Even though it is far less toxic than its organic compounds, elemental mercury still poses significant environmental pollution and remediation problems due to the fact that mercury forms such organic compounds inside living organisms. Inorganic mercury is less toxic than organic compounds (molecules containing carbon).

[edit] Treatment

The Standard of Care for mercury poisoning is chelation therapy. Conventional medicine makes use of DMSA (US) along with DMPS and ALA (Ex-Soviet Union, Europe).

Alternative medicine makes use of these same substances along with others, such as vitamin C (ascorbic acid), EDTA and "high sulfur foods". However, it has been shown that inorganic mercury (Hg2+) bound to EDTA (a necessary step in EDTA-induced mercury chelation) forms a complex (HgEDTA) that is "potentially injurious to the neuronal cytoskeleton". [6] Homeopaths claim to have approaches to the symptoms of mercury poisoning. While these practitioners believe that their approaches can support the body's own ability to heal itself, and can thus help with the symptoms of mercury poisoning, the human body is incapable of removing mercury or other heavy metals from the brain.

[edit] Trivia

The phrase "Mad as a hatter" is likely a reference to mercury poisoning, as mercury-based compounds were once used in the manufacture of felt hats in the 19th century.[citation needed]

[edit] References

  1. ^ http://movies.commons.ucalgary.ca/showcasetv/mercury
  2. ^ http://www.cdc.gov/nip/vacsafe/concerns/thimerosal/default.htm
  3. ^ The Karen Wetterhahn story - University of Bristol web page documenting her death, retrieved December 9th 2006
  4. ^ OSHA update following Karen Wetterhahn's death
  5. ^ Emily Oken, Robert O. Wright, Ken P. Kleinman, David Bellinger, Chitra J. Amarasiriwardena, Howard Hu, Janet W. Rich-Edwards, and Matthew W. Gillman (2005). "Maternal Fish Consumption, Hair Mercury, and Infant Cognition in a U.S. Cohort" (PDF). Environmental Health Perspectives 113 (10): 1376-80. PMID 16203250.
  6. ^ Duhr EF, Pendergrass JC, Slevin JT, & Haley BE. HgEDTA complex inhibits GTP interactions with the E-site of brain beta-tubulin. Toxicol Appl Pharmacol. 1993 Oct;122(2):273-80. PMID 8212009

[edit] External links

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