Post on 05-Feb-2016
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Harshini Wickremasinghe May 5, 2011
Bio 464
Physical/Chemical PropertiesSilvery, heavy, mobile,
liquid phaseOnly liquid metal at room
temp.OdorlessMelting Point: -38.83oC Boiling Point: 356.73oCDensity: 13.55g.cm-3
Low melting point due to unique electron configuration
High surface tensionPoor conductor of heatGood conductor of
electricity
Chemical Properties Insoluble in waterDoes not react with oxygen in air very steadilyWhen heated, reacts with oxygen in air to form mercury
oxideAt high temp., Hg vaporizes to form highly toxic fumesExtremely toxic and rarely found free in natureOften found as mineral cinnabar, HgS Cinnabar heated in air -> Hg vapor is distilled & cooled
to form liquid Hg
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 formsAirborne mercury is primarily inorganic
mercuryMercury amalgams: used to extract
precious metals like gold and silver; dental fillings
History fun factsFound in Egyptian
tombs 1500 B.C Egyptians used in
cosmetics, causing some facial deformities!
Greeks: ointmentsChinese: prolong life;
good health
Uses/Applications
Used in thermometers, barometers, electrical switches, mercury vapor lamps, fluorescent lamps, paints, fungicides/insecticides/antiseptics
Dental amalgams, battery manufacturing
Hg in the aquatic environmentAirborne mercury deposits
into groundRivers, streams and
wetlandsSulfate-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
Toxicity to aquatic lifeOnce 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
Toxic effects cont.Mercury compounds are acutely toxic to freshwater
microorganismsFreshwater fish show lethal response to mercury in acute
concentrations starting at 30ug/LThe 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)
DetoxificationThe 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
So how does it go from aquatic life to humans?
Toxicity effects on humansMethyl 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
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
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)
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