environmental chemistry chapter 11: toxic heavy metals - mercury copyright © 2007 by dbs
TRANSCRIPT
Concepts
• Sources of Mercury• Fate and Transport• Case Studies• History of Global Mercury Pollution
IntroductionQuicksilver!
• 1 of only 5 elements that are liquid at room temperature
• Heavy metal?
• Trace metal?
• Pathfinder element?
Sources
Natural (1/3)• Volcanic eruptions• Sedimentary erosion• Emissions from earth’s
crust and ocean
Mineral: Cinnabar (HgS)
Anthropogenic (2/3)• Fossil Fuel Burning• Waste incinerationn• Mining• Smelters• Chlor-alkali Plants
x10
Biosynthetic• Biological methylation
AnthropogenicSources
Coal: ~ 1 ppm
Any other material with this content = hazardous waste
Hg from coal burning has been found at both Poles
SourceSource Mg/yr Mg/yr (N. America)(N. America)
Electrical utilitiesElectrical utilities 52.752.7
IncineratorsIncinerators 32.232.2
Coal burning: Coal burning: residential and residential and industrialindustrial
12.812.8
MiningMining 6.76.7
Chlor-alkaliChlor-alkali 6.756.75
MiscMisc 64.164.1
TotalTotal 200.1200.1
Seigneur et al. 2004
Uses
1. industrial chemicals – e.g. drugs, fungicides, and as a cathode in chlorine and sodium hydroxide production (chlor-alkali process)
Cl2 ←NaCl → Na
H2 + NaOH ← Amalgam
2. electronics – switches, batteries, electrodes, mercury vapor + fluorescent lamps3. scientific instruments – barometer, thermometer, blood-presure meter4. pesticides5. Dentistry – amalgams6. gold and silver extraction for mining7. Skin lightening creams
Na forms amalgam with Hg, otherwise Na would explode on contact with water
Hg
Speciation
Mercury Ion Hg2+
AKA ‘reactive gaseous’ mercury’ (RGM) e.g. HgCl2(g)
Methyl MercuryCH3Hg+
Elemental MercuryHg0
Particulate bound Hg-P
Inorganic Organic
ReactiveVolatile
Global Regional ?
Dimethyl MercuryCH3HgCH3
Emisson and Deposition
‘Watershed Sensitivity’ creates localized ‘hot-spots’ of Hg accumulation
Hg0 → Hg2+
‘smog’
Cl.
OH.
Mercury deposition is enhanced by:
Oxidizing species
Particulate matter
Forest cover
Proximity to sources
Fate
Both bioaccumulate x106
High: Shark, swordfish, king mackeral, albacore tunaLow: shrimp, tilapia, salmon, pollock, catfish
Methylmercury
• Methylmercury is in reality
CH3HgCl and CH3HgOH
– Written:
CH3HgX, MeHg or CH3Hg+
(Misleading since it is covalent)
• Occurs in anaerobic portion of lakes– degraded by sunlight, most
important sink
O’neill diagram vs. Winfrey and Rudd, 1990
Health EffectsToxicity
• Toxicity: all forms
MeHg >> vapor >> Hg2+ >> liquid
– Liquid Hg is readily excreted– Hg2+ not readily transported across membranes – affects liver + kidneys– Vapor – diffuses from lungs to bloodstream to brain
• Methylmercury is lipophillic (soluble in fatty tissue)– More mobile – bioconcentrates, bioaccumulates and biomagnifies– Crosses blood-brain barrier– Converted to Hg2+ in brain (neurotoxin)
Usual barrier to Hg2+ is circumvented by vapor and MeHg
Health Effects Toxicity
• Pathways: Inhalation, ingestion, dermal
• Most Hg in humans is MeHg from fish
• FDA: 1 ppm fish / EPD: 2.0 ppb water
• Brain damage, nervous system disorders, heart disease, liver and kidney failure
• Symptoms: all brain associated, - numbness of limbs, loss of vision, hearing and muscle coordination
• Largest risk to newborns
Health EffectsMode of Action
• Biochemical mode of action: inhibition of enzymes
Affinity for-SH (sulfhydryl groups)
• Occur in enzymes which control metabolic pathways
M2+ + 2 R-S-H → R-S-M-S-R + 2H+
Health EffectsMode of Action
• Hg dissolves neuronshttp://commons.ucalgary.ca/mercury/
Case StudyMinamata, 1953
• Minamata Bay, Japan (1953-1960)• Plastic manufacturer (Chisso Corp.), used mercury in the
production of acetaldehyde• Discharged mercury into the bay• Main diet of locals was fish + shellfish
– 5-20 ppm (106 water)• Over 3,000 people suffered (730 deaths):
Minamata disease / Dancing Cat Disease
various deformities, damage to nervous system, retardation or death
• Developing embryos are especially vulnerableWHO limit 0.5 mg kg-1
Minamata 50 mg kg-1
History of Mercury Pollution
Martínez-Cortizas et al., 1999
Site: Almadén, Spain
World’s largest Hg mine
Pathways
• Acidification of lakes enhances solubility and methylation rates
• Double-whammy effect of burning fossil-fuels
Lean, 2003
Conc. Hg in standardized fish in 84 Ontario lakes
Solutions
• Stop burning coal…not going to happen
• Pollution control measures – oxidation, electrostatic ppt
• Vegetarian fishes!
Further ReadingJournals and Reports
• Betts, K. (2003) Dramatically improved mercury removal. Environmental Science and Technology, pp. 283-284A.
• Cleckner, L.B., Garrison, P.J., Hurley, J.P., Olson, M.L., and Krabbenhoft, D.P. (1998) Trophic transfer of methyl mercury in the northern Florida Everglades. Biogeochemistry, Vol. 40, No. 2-3, pp. 347-361.
• Crenson, S.L. (2002) Study Records Elevated Mercury. Associated Press. Sunday Oct 20th.
• Fitzgerald, W.F., Engstrom, D.E., Mason, R.P., and Nater, E.A. (1998) The case for atmospheric mercury contamination in remote areas. Environmental Science and Technology, Vol. 32, pp. 1-7.
• Lean, D. (2003) Mercury pollution a mind-numbing problem: high levels of mercury lurk in our water supply, and it is time to sound a global alarm. Canadian Chemical News, January, p. 23.
• Martínez-Cortizas, A., Pontrevedra-Pombal, X., Garcia-Rodeja, E., Nóvoa-Muñoz, J.C., and Shotyk, W. (1999) Mercury in a Spanish peat bog: Archive of climate change and atmospheric deposition. Science, Vol. 284, pp. 939-942.
• Pacya, E.G., and Pacya, J.M. (2002) Global emission of mercury from anthropogenic sources in 1995. Water, Air and Soil Pollution, Vol. 137, pp. 149-165.
• Renner, R. (2004) Mercury woes appear to grow. Environmental Science and Technology, Vol. 38, No. 8, pp. 144A.
• Rouhi, A.M. (2002) Mercury Showers. Chemical and Engineering News. April 15, p. 40
• Sarr, R.A. (1999) New Efforts to Uncover the Dangers of Mercury. New York Times, Health and Fitness Section, p. D7, Tuesday, November 2.
• Seigneur, C., Vijayaraghaven, K., Lohman, K., Karamchandanai, P., and Scott, C. (2004) Global source attribution for mercury deposition in the United States. Environmental Science and Technology, Vol. 28, No. 2, pp. 555-569.
• Winfrey, M.R., Rudd, J.W.M., 1990. Environmental factors affecting the formation of methylmercury in low pH lakes. Environmental Toxicology and Chemistry, Vol. 9, pp. 853-859.
• Wright, K. (2005) Our Preferred Poison. Discover, March.
Books
• Berry, L.G. and Mason, B. (1959) Mineralogy: Concepts, Descriptions, and Determinations. W.H. Freeman, San Francisco.
• Gribble, C.D. (1978) Rutley’s Elements of mineralogy, 27th edition. Unwin Hyman, London
• HBRF (2007) Mercury Matters. Hubbard Brook Research Foundation.
• O’neill, P. (1993) Environmental Chemistry (2nd edition). Chapman and Hall.
Movies
• FHS: the Ocean Sink (1990) 29 mins
• FHS: Chemicals from NaCl: 1 20 mins
• FHS: Salt 1992
• Minamata movie: http://science.education.nih.gov/supplements/nih2/Chemicals/videos/act5/minamata.htm
• People's Century: Endangered Planet (1999)