Mercury: A Most Interesting and Toxic Metal

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Mercury A Most Interesting and Toxic Metal

• Enrichment Program in Chemistry
• March 23, 2004

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Intoduction

• Sometimes I tell students to put down pen and to
  not be just copy machines but to think
• On my Web page, Academics, Departments,
  Chemistry, Faculty/staff, Miller
• URLwww.roanoke.edu/Chemistry/Miller/Mercury.ppt

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First Image for Word Mercury?
Planet?
Automobile?
Dense, silvery liquid?
Poison?
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More Specifically
Metal
Liquid metal
Compound, salt
MeHg, Me2Hg
A poison
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Goals of Talk

• Better understand mercury and its compounds
  general in general
• Relate some of its properties to General
  Chemistry topics
• Better understand its toxicity
• Better understand its environmental sources

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Outline of Talk

• Introductory Chemistry
• Occurrence
• Physical properties of elemental form
• Chemical properties of elemental form
• Uses, elemental form and compounds
• Toxicities
• Safe limits
• Cases of Poisonings

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Introductory Chemistry

• Based on periodic table

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Introductory Chemistry

• Based on periodic table
• Metal or nonmetal
• Ionic or covalent
• Elemental form?
• But, . . .
• Oxidation state
• Metals positive
• Charge ?
• Hg, HgCl, Hg2Cl2, HgCl2

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Introductory Chemistry, cont.

• Physical state of elemental form
• s. l. g?
• Physical state of compounds
• Salts
• MeHg
• MeHg1
• Me2Hg

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Summary of Introductory Chemistry

• The mercury we will be talking about
• A gas, Hg0(g)
• A liquid, Hg0(l)
• An ionic solid, which is usually somewhat soluble
  in water, Hg2(aq)
• An organometallic ion dissolved in water,
  MeHg1(aq) CH3Hg1(aq)
• A volatile, liquid organometallic compound, Me2Hg
  (CH3)2Hg

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Occurrence

• AKA quicksilver, occasionally found free
• Cinnabar ore (HgS) in Spain and Italy
• Important salts include
• mercuric chloride, HgC12 (corrosive sublimate)
• mercurous chloride, Hg2Cl2, calomel, was used in
  medicine
• mercury fulminate, Hg(ONC)2, detonator for
  explosives
• mercuric sulfide, HgS, vermilion, high-grade
  paint pigment

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Phys Properties of Elemental Form

• Liquid, freezing point of 39 C (or F)
• Boiling point of 357 C
• Vapor pressure at 25 C of 0.0018 Torr
• Vaporizes slowly
• Density 13.5 g/mL
• Solubility in H2O 0.002 g/100 g H2O at 20ºC
• Forms amalgams

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Concentration of Saturated Vapor

• Vp of 0.0018 Torr _at_ 25 C
• Using PVnRT, gives 20 mg Hg/m3
• The regulatory threshold limit for mercury vapor
  for continuous 40 hour per week exposure is 0.05
  mg Hg/m3
• Meaning No adverse affects at this
  concentration

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Chemical Properties

• Stable in air at room temperature, slowly
  oxidizes at elevated temperatures,
• Not attacked by water, HCl(aq), H2SO4
• Dissolves in dilute HNO3
• Above are abiotic reactions. Many important
  environmental reactions are controlled by
  organisms.
• See biogeochemical cycle on next slide

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From Web page of Dr. Tamar Barkay at Rutgers
University.
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Uses

• Thermometers, barometers, electrical switches,
  pesticides, was used in gold recovery from mining
• In 1731 and 1732 it was fashionable in London
  and Edinburgh to take one ounce of quick silver
  every morning for several weeks
• The internal use of calomel was accompanied by
  gastrointestinal symptoms so drastic that in the
  19th century, not only chloride of mercury but
  also the other forms fell into general disfavor.
• Cleanup vacuum, sulfur, zinc, brush?

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Toxicity (Hg, Hg2, MeHg1)

• Acute, chronic?
• Lethal, neurotoxic, carcinogenic?
• Inhalation, ingestion, skin contact?
• Many possible symptoms generally initial
  irritation, followed by kidney and nervous system
  damage (including personality changes)
• Overview

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More on Toxicity

• Inhalation Causes severe respiratory tract
  damage. Symptoms include sore throat, coughing,
  pain, tightness in chest, breathing difficulties,
  shortness of breath, headache, muscle weakness,
  anorexia, gastrointestinal disturbance, ringing
  in the ear, liver changes, fever, bronchitis and
  pneumonitis. Can be absorbed through inhalation
  with symptoms similar to ingestion.
• Ingestion may cause burning of the mouth and
  pharynx, abdominal pain, vomiting, corrosive
  ulceration, bloody diarrhea. May be followed by a
  rapid and weak pulse, shallow breathing,
  paleness, exhaustion, tremors and collapse.
  Delayed death may occur from renal failure.
  Gastrointenstinal uptake of mercury is less than
  5 but its ability to penetrate tissues presents
  some hazard. Initial symptoms may be thirst,
  possible abdominal discomfort.
• Skin Contact causes irritaton and burns to skin.
  Symptoms include redness and pain. May cause skin
  allergy and sensitization. Can be absorbed
  through the skin with symptoms to parallel
  ingestion.

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Even More on Toxicity

• Eye Contact causes irritation and burns to eyes.
  Symptoms include redness, pain, blurred vision
  may cause serious and permanent eye damage.
• Chronic Exposure chronic exposure through any
  route can produce central nervous system damage.
  May cause muscle tremors, personality and
  behavior changes, memory loss, metallic taste,
  loosening of the teeth, digestive disorders, skin
  rashes, brain damage and kidney damage. Can cause
  skin allergies and accumulate in the body.
  Repeated skin contact can cause the skin to turn
  gray in color. A suspected reproductive hazard
  may damage the developing fetus and decrease
  fertility in males and females.
• Aggravation of Pre-existing Conditions persons
  with nervous disorders, or impaired kidney or
  respiratory function, or a history of allergies
  or a known sensitization to mercury may be more
  susceptible to the effects of the substance.

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Safe Limits

• Inhalation, ingestion, skin contact?
• Skin contact irritant (probably long term or
  sensitized)
• Ingestion of HgCl2 rat oral LD50 is 210 mg/kg
• (If 160 lb rats ate 14 g, half would die)

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Safe Limits, Hg, Inhalation

• Effects on Animals
• Acute Toxicity
• Rabbits exposed for 4 h to saturated vapors of
  mercury (27 gm/m3) suffered severe poisoning of
  brain, color, heart, liver, lungs, and kidneys
  (Ashe et. al. 1953).
• Subacute Toxicity
• Guinea pigs exposed 10 h/d for 4 d to mercury
  vapor at 6 mg/m3 developed neurotic effects and
  hemorrhagic colitis. Mercury was stored in the
  kidneys. (Holzmann, 1931).
• Chronic Toxicity
• Dogs, rabbits and rats showed no effects when
  exposed to Hg vapor at 0.1 mg/m3 for 85 weeks.
  Fraser et. al., 1934)
• Emergency and Continuous Exposure Limits for
  Selected Airborne Contaminants, Volume 1, (1984),
  National Academy Press

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Safe Limits, Hg, Inhalation, cont.

• Airborne Exposure Limits
• OSHA Acceptable Ceiling Concentration mercury
  and mercury compounds 0.1 mg/m3 (TWA), skin
• ACGIH Threshold Limit Value (TLV) inorganic and
  metallic mercury, as Hg 0.025 mg/m3 (TWA) skin,
  not classifiable as a human carcinogen.

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Safe Limits, Fish

• 2004 EPA and FDA Advice for
• Women Who Might Become Pregnant
• Women Who are Pregnant
• Nursing Mothers
• Young Children
• One meal/week
• (Reference Dose (RfD) 1x10-4 mg/kg-d)

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Getting Mixed Messages?

• I hope so
• Ingestion rat oral LD50 is 210 mg/kg
• For fish reference dose is 1x10-4 mg/kg-d

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Sort Out the Messages

• Acute, lethal
• One dose, to kill one out of two healthy people
• Chronic, small neuro changes
• Very small doses over long periods of time, to
  prevent baby or young child from having slightly
  lower IQ or slightly impaired nervous system

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How Does the Hg Get Into the Fish?

• Biogeochemical cycle seen earlier

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Chemistry of Mercury Toxicity

• Complex, incompletely understood
• Involves sulfur-containing molecules in the
  organisms (Hg-S bonds are very strong)

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Current Sources of New Hg

• US emitting about 150 tons Hg/year
• About 90 from combustion (wastes and power
  generation)
• However, a lot of Hg is stored in the
  environment and being recycling

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What Can We Do? What Should We Do?
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Cases of Poisonings

• Mad Hatter
• Child playing with Hg in Las Vegas
• Thimerosal (mercury poisoning from preservative
  in vaccines, related to autism?)
• Dental amalgams
• Mercury poisoning associated with beauty cream -
  Texas, New Mexico, and California, 1995 - 1996