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