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A Small Dose of Hg

A Small Dose of Hg. An Introduction To The Health Effects & Risk of Mercury Exposure. ENV H 472 A - ENVIRONMENTAL RISK AND SOCIETY Class 4. Child Health. Hazard + Exposure = Risk. Key Words of Toxicology. Dose / Response. Individual Susceptibility. Mercury the Metal.

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A Small Dose of Hg

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  1. A Small Dose of Hg An Introduction To The Health Effects & Risk of Mercury Exposure ENV H 472 A - ENVIRONMENTAL RISK AND SOCIETY Class 4

  2. Child Health

  3. Hazard + Exposure = Risk Key Words of Toxicology Dose / Response Individual Susceptibility

  4. Mercury the Metal

  5. Methyl Mercury (MeHg) Hg CH3

  6. Hg - Inorganic & Organic Hg Inorganic – Quick Silver Hg CH3 Organic – Methyl Mercury

  7. Hg Facts & Uses • Quicksilver • 13.6 times the weight of water • Evaporates at room temperature • Bacteria change to Methylmercury • Amalgam • Many Industrial uses (thermometers, chemical reactions, gold mining)

  8. Hg – Like Water

  9. Hg – Solid Enough to Sit On

  10. Ancient Awareness • Alchemy • Medicine - cure syphilis? • Egyptian tomb -1500 BC

  11. Greek God Mercury “For then she bare a son, of many shifts, blandly cunning, a robber, a cattle driver, a bringer of dreams, a watcher by night, a thief at the gates, one who was soon to show forth wonderful deeds among the deathless gods...” Description of the birth of the Greek God Mercury

  12. Historical Events Occupational Exposure Gold mining. Hatters in the felt industry.

  13. Historical Awareness

  14. Polluting with HG Discharge in Minamata Bay

  15. Fetal Effects of MeHg

  16. Life-Long Effects of MeHg

  17. Planting Seed with Mercury

  18. Iraq Mothers with Bread

  19. Iraq Infant - Effects of Mercury

  20. Coal Fired Plants – Hg Emissions

  21. Outbreaks of MeHg Poisoning

  22. Mercury to Methyl Mercury Inorganic - elemental mercury vapor Hg0 Biotransformation Organic - Methylmercury - CH3Hg+ Bioaccumulation

  23. Mercury Release 50-75% mercury of released in the environment related to human activities

  24. Atmospheric Hg

  25. Biotransformation of Mercury Inorganic Mercury Discharge Ambient Water Sediments Biomethylation Methyl-Mercury Bioaccumulation Edible Fish Exposure Methyl-Mercury In Humans

  26. Environmental Sources of Mercury Hg0 Hg2+ CH3Hg+ • Natural Degassing of the earth • Combustion of fossil fuel • Industrial Discharges and Wastes • Incineration & Crematories • Dental amalgams

  27. The Mercury Cycle

  28. Neurobehavioral Effects • Blindness - Deafness • Cerebral Palsy - Seizures • Abnormal reflexes & muscle tone • Retarded motor development • Visual and Auditory Deficits • Delayed motor development • Altered DRH performance

  29. Effects On The Brain • Decrease in Brain Size • Cell loss • Disorganization of cells • Cell migration failures

  30. Uncertainty How do you know? How good is the data?

  31. Use of Uncertainty Factors • Divide Dose by Power of 10 • Human variability • Interspecies extrapolation • Children • Subchronic to chronic extrapolation • Absence of a NOAEL • Database uncertainty

  32. Use of Uncertainty Factors Animal Dose Response Data NOAEL (No Observed Adverse Effect Level) Divide by 10 (Account for inadequate animal data) Divide by 10 (Animal to Human Extrapolation) Divide by 10 (Human Variability or Individual Sensitivity) Reference Dose (RfD) Or Acceptable Daily Intake (ADI)

  33. Reducing Uncertainty • Upstanding mechanism of action • Physiologically based pharmacokinetic models (distribution and metabolism) • Sample size

  34. Animal - Risk Assessment • MONKEY - 25 µg/kg - LOAEL • RAT - 10 µg/kg - LOAEL • RAT - 50 µg/kg - replicated

  35. Animal - Risk Assessment • 2.5 µg/kg - NOAEL (animals) • 0.25 µg/kg - Human • 0.025 µg/kg - Sensitive populations (the rule of dividing by 10)

  36. Human - Risk Assessment • 10-20 ppm hair - LOAEL • • 40-80 ppb blood - LOAEL • • 0.645 µg/kg • • 0.06 µg/kg - RfD •

  37. Mercury Fishing Advisories • In 2000, 41 States have over 2000 fish consumption advisories • An increase form 27 in 1993 • Pregnant women, nursing mothers, women who intend to have children, and children under 15

  38. Recommendations • Reduce environmental release • Restrict global production and sale • Advise women of child bearing age • Research mechanisms of action • Assess neurodegenerative effects

  39. MeHg Consumption Limits US EPA – 0.1 ug/kg-day US FDA – 1 ppm (mg/kg) in tuna

  40. WA State Advisory Limit the amount of canned tuna you eat, based on your bodyweight. Guidelines are: Women of childbearing age should limit the amount of canned tuna they eat to about one can per week (six ounces.) A woman who weighs less than 135 pounds should eat less than one can of tuna per week. Children under six should eat less than one half a can of tuna (three ounces) per week. Specific weekly limits for children under six range from one ounce for a twenty pound child, to three ounces for a child weighing about sixty pounds. http://www.doh.wa.gov/fish/FishAdvMercury.htm

  41. WA State Hg CAP • WA State Mercury Chemical Action Plan • Reduce Hg in fish • Reduce Hg release into the environment • 4-5 tons of Hg released in WA • Educating consumers about Hg in home http://www.ecy.wa.gov/biblio/0303001.html http://www.ecy.wa.gov/programs/eap/pbt/mercuryplan.html

  42. Hg CAP and Trade • U.S. EPA Produced • “First-Ever Rule to Reduce Mercury Emissions from Power Plants” • Last 15 years no drop in Hg emissions from power plants • Is Cap and Trade appropriate for a demonstrated neurotoxic compound?

  43. Mercury A Global Issue Mercury distribution and exposure is a global problem

  44. Precautionary Principle "When an activity raises threats of harm to the environment or human health, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically." - Wingspread Statement on the Precautionary Principle, Jan. 1998

  45. Alice’s Adventures “Everything’s got a moral, if you can only find it” Lewis Carroll in Alice’s Adventures in Wonderland

  46. Knowledge - Responsibility • Children have a right to a safe, fair and healthy environment • Ethical Responsibility to share and use of knowledge • Duty to promote health and well being of children • Thoughtful public health advocate

  47. Mercury or Lead Questions or Comments?

  48. Additional Information - Hg • Web Sites • World Health Organization - global prospective on mercury health effects. http://www.who.int/water_sanitation_health/GDWQ/Chemicals/mercuryfull.htm • US EPA - Main site on Mercury. http://www.epa.gov/mercury/ • The Mercury Policy Project (MPP). - works to raise awareness about the threat of mercury contamination - http://www.mercurypolicy.org/ • www.asmalldoseof.org

  49. Authorship Information This presentation is supplement to “A Small Dose of Toxicology” For Additional Information Contact Steven G. Gilbert, PhD, DABT E-mail: smdose@asmalldoseof.org Web: www.asmalldoseof.org

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