A Small Dose of Hg

Small Dose of Mercury A Small Dose of Toxicology

A Small Dose of Hg

An Introduction To The Health Effects & Risk of

Mercury ExposureENV H 472 A - ENVIRONMENTAL

RISK AND SOCIETYClass 4

A Small Dose of Toxicology Small Dose of Mercury

Child Health

Key Words of Toxicology

Hazard + Exposure = Risk

Individual Susceptibility

Dose / Response

Mercury the Metal

Methyl Mercury (MeHg)

Hg - Inorganic & Organic

Inorganic – Quick Silver

Organic – Methyl Mercury

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)

Hg – Like Water

Hg – Solid Enough to Sit On

• Alchemy• Medicine - cure syphilis?• Egyptian tomb -1500 BC

Ancient Awareness

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

Occupational ExposureGold mining.

Hatters in the felt industry.

Historical Events

Historical Awareness

A Small Dose of Toxicology Small Dose of Mercury Polluting with HG

Discharge in Minamata Bay

Fetal Effects of MeHg

Life-Long Effects of MeHg

Planting Seed with Mercury

Iraq Mothers with Bread

Iraq Infant - Effects of Mercury

Coal Fired Plants – Hg Emissions

Outbreaks of MeHg Poisoning

Place Year CasesMinamata 1953-60 1000

Nigata 1964-65 646

Guatemala 1963-65 45

Ghana 1967 144

Pakistan 1969 100

Iraq 1956 100

Iraq 1960 1,002

Iraq 1971 40,000

On-going 2001 ???

Inorganic - elemental mercury vapor Hg0

Biotransformation

Organic - Methylmercury - CH3Hg+

Bioaccumulation

Mercury to Methyl Mercury

Mercury Release

50-75% mercury of released in the environment related to human activities

Atmospheric Hg

Ambient WaterSediments

Edible Fish

Inorganic Mercury

Methyl-Mercury

Methyl-MercuryIn Humans

Biomethylation

Bioaccumulation

Exposure

Discharge

Biotransformation of Mercury

• Natural Degassing of the earth• Combustion of fossil fuel• Industrial Discharges and Wastes• Incineration & Crematories• Dental amalgams

Hg0 Hg2+ CH3Hg+

Environmental Sources of Mercury

The Mercury Cycle

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

Neurobehavioral Effects

• Decrease in Brain Size• Cell loss• Disorganization of cells• Cell migration failures

Effects On The Brain

How do you know?How good is the data?

Uncertainty

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

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)

Reducing Uncertainty

• Upstanding mechanism of action• Physiologically based

pharmacokinetic models (distribution and metabolism)

• Sample size

MONKEY - 25 µg/kg - LOAELRAT - 10 µg/kg - LOAELRAT - 50 µg/kg - replicated

Animal - Risk Assessment

2.5 µg/kg - NOAEL (animals) 0.25 µg/kg - Human 0.025 µg/kg - Sensitive populations

Animal - Risk Assessment

(the rule of dividing by 10)

• 10-20 ppm hair - LOAEL •• 40-80 ppb blood - LOAEL •

• 0.645 µg/kg •• 0.06 µg/kg - RfD •

Human - Risk Assessment

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

• Reduce environmental release

• Restrict global production and sale

• Advise women of child bearing age

• Research mechanisms of action

• Assess neurodegenerative effects

Recommendations

MeHg Consumption Limits

US EPA – 0.1 ug/kg-day

US FDA – 1 ppm (mg/kg) in tuna

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.

WA State Advisory

http://www.doh.wa.gov/fish/FishAdvMercury.htm

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

WA State Hg CAP

http://www.ecy.wa.gov/biblio/0303001.html

http://www.ecy.wa.gov/programs/eap/pbt/mercuryplan.html

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?

Hg CAP and Trade

Mercury A Global Issue

Mercury distribution and exposure is a global problem

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

Alice’s Adventures

“Everything’s got a moral, if you can only find it”

Lewis Carroll in Alice’s Adventures in Wonderland

• 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

Knowledge - Responsibility

Mercury or Lead

Questions or Comments?

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

Authorship Information

For Additional Information ContactSteven G. Gilbert, PhD, DABT

E-mail: smdose@asmalldoseof.orgWeb: www.asmalldoseof.org

This presentation is supplement to “A Small Dose of Toxicology”

A Small Dose of Hg

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