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Mercury: Properties, Uses, and Toxicity

This article discusses the physical and chemical properties of mercury, its historical uses, its presence in the environment, and its toxicity to aquatic life and humans. It also explores detoxification processes and the role of selenium in protecting against mercury toxicity.

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Mercury: Properties, Uses, and Toxicity

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  1. Harshini Wickremasinghe May 5, 2011 Bio 464

  2. Physical/Chemical Properties • Silvery, heavy, mobile, liquid phase • Only liquid metal at room temp. • Odorless • Melting Point: -38.83oC • Boiling Point: 356.73oC • Density: 13.55g.cm-3 • Low melting point due to unique electron configuration • High surface tension • Poor conductor of heat • Good conductor of electricity

  3. Chemical Properties • Insoluble in water • Does not react with oxygen in air very steadily • When heated, reacts with oxygen in air to form mercury oxide • At high temp., Hg vaporizes to form highly toxic fumes • Extremely toxic and rarely found free in nature • Often found as mineral cinnabar, HgS • Cinnabar heated in air -> Hg vapor is distilled & cooled to form liquid Hg

  4. Properties contd. • 7 natural occurring isotopes; 202Hg being the most abundant (29.86%) • ~ 12 radioactive isotopes known • Longest lived 194Hg with half life of 444yrs • 197Hg & 203Hg used to study brain and kidney • Mercury exists in 3 oxidation states • Organics (esp. CH3Hg(II)X) most toxic forms • Airborne mercury is primarily inorganic mercury • Mercury amalgams: used to extract precious metals like gold and silver; dental fillings

  5. History fun facts • Found in Egyptian tombs 1500 B.C • Egyptians used in cosmetics, causing some facial deformities! • Greeks: ointments • Chinese: prolong life; good health

  6. Uses/Applications • Used in thermometers, barometers, electrical switches, mercury vapor lamps, fluorescent lamps, paints, fungicides/insecticides/antiseptics • Dental amalgams, battery manufacturing

  7. Hg in the aquatic environment • Airborne mercury deposits into ground • Rivers, streams and wetlands • Sulfate-reducing bacteria buried in sediment transforms the inorganic Hg into CH3Hg • Bioaccumulates in fish, aq. inverts. and mammals • Conc. of Hg in organism increases with increasing trophic level in food chain • Larger predatory game fish have higher levels of Hg • Hg concentrates in muscle tissue of fish

  8. Toxicity to aquatic life • Once mercury is in surface water it goes through complex cycle • Brought down to sediment and into food chain or released back into atmosphere • Levels of dissolved organic carbon and low pH levels enhance mobility of Hg making it more likely to enter food chain

  9. Toxic effects cont. • Mercury compounds are acutely toxic to freshwater microorganisms • Freshwater fish show lethal response to mercury in acute concentrations starting at 30ug/L • The LC50/96-hour values for fish are less than 1 mg/L. • Many aquatic inverts. are very sensitive to mercury (esp. larvae) • Methyl mercury passes the blood brain-barrier and nuclear membranes to react directly with cellular and nuclear components • Accumulation of Hg in the brain, compared to blood and muscle, is much less is fish than mammals (lack external barriers and internal detoxification system)

  10. Detoxification • The liver is the main site for methyl Hg biotransformation in animals • Liver transforms harmful compounds into metabolites which are excreted into bile and detoxification continues • Once in the bile, compound enters small intestine and either reabsrobed in gut or excreted through feces • However…. • Methyl mercury undergoes enterohepatic cycle • Liver-bile-small intestine-reabsorbed into blood-back to liver • Hg is retained by the organism and has a significant increased half life • Many studies also indicate Se plays a role in protecting against Hg toxiciy

  11. So how does it go from aquatic life to humans?

  12. Toxicity effects on humans • Methyl mercury from fish consumption (highly toxic) or breathing vaporous mercury (bodies are more adapted to reducing toxic effects) • Methyl mercury affects central nervous system and irreversible brain damage

  13. 2 Biggest Hg poisonings • “Mad Hatter”- during the industrial revolution, hat-makers used mercury nitrate to soften fur used as lining in hats. Toxic effected brains causing mental instability. • Japan - 1952, chemical co. dumped Hg into Minamata harbor; residents of local fishing villages contaminated; 100s affected and 68 died

  14. Hazardous!! • DANGER! CORROSIVE. CAUSES BURNS TO SKIN, EYES, AND RESPIRATORY TRACT. MAY BE FATAL IF SWALLOWED OR INHALED. HARMFUL IF ABSORBED THROUGH SKIN. AFFECTS THE KIDNEYS AND CENTRAL NERVOUS SYSTEM. MAY CAUSE ALLERGIC SKIN REACTION. (MSDS 2008)

  15. Bibliography • Chemistry Explained: Functions and Applications. “Mercury” http://www.chemistryexplained.com/elements/L-P/Mercury.html • Chemical of the Week. “Mercury” http://scifun.chem.wisc.edu/chemweek/mercury/mercury.htm • “Ecological effects, transport, and fate of mercury: a general review” linkinghub.elsevier.com/retrieve/pii/S0045653599002830 • “Biochemical effects of Mercury, Cadmium, and Lead” http://www.annualreviews.org/doi/pdf/10.1146/annurev.bi.41.070172.000515 • U.S. Geological Survey. “Mercury Contamination of Aquatic Ecosystems” http://water.usgs.gov/wid/FS_216-95/FS_216-95.html • “Handbook on the toxicology of metals” http://books.google.com/books?hl=en&lr=&id=nKulgztuzL8C&oi=fnd&pg=PP1&dq=handbook+on+the+toxicology+of+metals&ots=QRRSdjvi0v&sig=VKvf3FpqfVq6nPa4viCV5RRrT3I#v=onepage&q&f=false • MSDS: Mercury http://www.veegee.com/msds/m1001.pdf

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