Environmental Chemistry

Chapter 11:Toxic Heavy Metals - Mercury

Copyright © 2007 by DBS

Quote“the metal that slipped away”

-from Wisconsin Natural Resources Magazine, Katherine Esposito

Connections

What is a Heavy Metal?

NYT 110299

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?

End

• Review

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

Pathways

End

• Review

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

Atmosphere

Waterways

[O]

1-20μg m2 yr-1

USGS

Fish

pH/DOC

UV

Watershed-Lake Cycling

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/

End

• Review

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

End

• Review

History of Mercury Pollution

Martínez-Cortizas et al., 1999

Site: Almadén, Spain

World’s largest Hg mine

History of Mercury Pollution

End

• Review

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

Pathways

Grasshopper Effect

End

• Review

Solutions

• Stop burning coal…not going to happen

• Pollution control measures – oxidation, electrostatic ppt

• Vegetarian fishes!

End

• Review

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)