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Occupational and Environmental Chemical Exposures Heavy Metals: Lead and Mercury. Mary McDaniel, D.O., J.D., M.P.H. McDaniel Lambert Inc. mfmcdaniel@mclam.com UCLA February 21, 2006. Who’s at Risk?. Occupational Exposure Household exposure Ambient exposure

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Occupational and environmental chemical exposures heavy metals lead and mercury l.jpg

Occupational and Environmental Chemical Exposures Heavy Metals: Lead and Mercury

Mary McDaniel, D.O., J.D., M.P.H.

McDaniel Lambert Inc.



February 21, 2006

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Who’s at Risk?

  • Occupational Exposure

  • Household exposure

  • Ambient exposure

  • For many chemicals, fetuses, infants and/or children are at greatest risk due to susceptibility to toxic effects and/or increased exposure

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  • Long history of human exposure (5000 yrs plus).

  • Thought to have been responsible for downfall of Greek and Roman civilizations.

  • Widespread environmental contaminant.

  • Childhood lead poisoning was first described in Australia 100 years ago

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Sources of Lead Exposure – Ingestion and Inhalation

  • Occupational – lead mines, smelters and refiners, plumbers, auto repair, police officers, glass manufacturers, battery manufacturers.

  • Hobbies – glazed ceramics, target shooting, soldering (electronics, stained glass), painting, home repair activities.

  • Environmental – leaded gasoline and paints, water from corroded pipes, earthenware, contaminated soil and dust, imported canned foods/candy

  • Substance use – folk remedies, health foods

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Nutrition and Lead

  • Ingestion of lead during a period of fasting results in greater absorption

  • Dietary intake of calcium has a very significant effect on lead uptake

    • Rats on a low-calcium diet had four times higher blood lead concentrations than rats on a normal diet

  • Intake of iron is also important with low levels increasing the uptake of lead

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Lead Health Effects

  • Interferes with normal cell function and various physiological process: peripheral and central nervous systems, blood cell production, metabolism of vitamin D and calcium, kidneys, reproductive system

  • Probable human carcinogen (classified B2 by USEPA)

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Lead Health Effects (cont.)

  • Children and pregnant women at highest risk

    • Children – higher exposures and postnatal susceptibility

    • For every 10 ug/dl increase in concentration there is a one to three-point drop in IQ

    • Pregnant women – lead crosses the placenta and damages nervous system

    • Lead in the fetus tends to equilibrate with maternal lead

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Lead Health Effects (cont’d)

  • Symptoms of lead poisoning

    • Early symptoms are vague and nonspecific

    • Pallor, vomiting, abdominal pain, constipation, stupor, loss of appetite, irritability, and loss of muscular coordination

    • Classic signs include lead colic, lead “lines” on the gums and wrist drop

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Lead Biological Fate

  • Inorganic lead not metabolized – directly absorbed, distributed and excreted

  • Inhaled lead completely absorbed; typically 10-15% of ingested lead absorbed from the GI tract

  • Lead half lives in adults

    • Blood – 25 days

    • Soft tissue – 40 days

    • Bone – 25+ years

  • Lead poisoning does not require major acute exposure - body accumulates over lifetime and releases slowly

  • Under stress, body may metabolize lead stores, thus increasing blood lead levels

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Health Effects at Various Blood Lead Levels

Health Effect (ug/dl)Blood Lead

Level of concern for fetal effects <10

Blood enzyme changes 15-20

IQ deficiencies in children <25

Clinical anemia, children 40

Clinical anemia, adults 50

Reproductive effects in adults 50

Mental losses (writing/speech 50-60

problems, retardation)

Irreversible brain damage 100

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Lead Standards and Regulations

Blood Levels

CDC Advisory – level of concern for children 10 ug/dL

OSHA – level of concern 40 ug/dL

OSHA Regulation – medical removal from exposure 50 ug/dL

Air Concentrations

OSHA Action level 30 ug/m3

OSHA Regulation – PEL 50 ug/m3

US EPA – ambient air quality standard (3 month average) 1.5 ug/m3


EPA – drinking water action level 15 ug/L

CalEPA – drinking water public health goal 2 ug/L

CalEPA – drinking water maximum contaminant level 15 ug/L

FDA – food advisory level 100 ug/day

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Poverty and Lead Poisoning

  • Impact greatest among urban poor

    • Older housing more lead based paints and lead contaminated soils

    • Older schools

  • 4.5% of all 1 to 2 year-old children have blood lead levels >10 ug/dl

  • 21.6% of 1 to 2 year-old black children have blood lead levels >10 ug/dl

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Blood Lead Levels for Various Groups of People

Rural Children 7-11

Urban Children 9-33

Adults 15-22

Children near smelter 35-68

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  • Exposure Interviews

    • Occupation, housing, lifestyle/hobbies, school exposures, pica child

  • Signs and Symptoms: most persons with lead toxicity are not overly symptomatic

    • Continuum includes increasing severity of fatigue, irritability, lethargy, abdominal pain

    • School

    • Pica

  • Blood lead level is best screening and diagnostic test

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  • Depends on exposure level

  • Limit exposure

    • May be only therapy needed for asymptomatic patients with blood levels below 25 ug/dL

  • Dietary changes

    • Ca supplements

  • Chelation therapy (e.g. calcium disodium EDTA)

    • CDC recommends immediate chelation therapy for children with blood levels of 45 ug/dL and above

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  • Long history of use

    • Metallic mercury used as a laxative

    • Mad Hatters disease from use in felt manufacture

    • Andrew Jackson thought to have died from mercuric chloride treatment

    • “Dancing Cat Disease”

  • Chemistry

    • Exists in 3 forms: elemental, inorganic salts and organic

    • Elemental (metallic) mercury (Hg0) can be converted to organic methylmercury (MeHg) in the environment by the action of bacteria

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Sources of Mercury Exposure

  • Highest exposures have been from industrial or pesticide poisonings (Minamata, Japan – Chlor-alkali; Iraq – Wheat fungicide)

  • General population mostly exposed by eating contaminated fish (methylmercury)

    • Fish bioaccumulate methyl mercury with 99% of mercury in fish in the the methylated form

    • Older and larger carnivorous fish have the highest levels (swordfish, tuna, shark, king mackerel)

    • Can of tuna contains 0.20 ppm

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Sources of Mercury Exposure (cont.)

  • Occupational (primarily elemental mercury vapor) – chlor-alkalai plants, laboratory personnel, miners and processors of cinnabar, gold, silver, copper, and zinc, metallurgists, ectroplaters, explosive manufacturers

  • Hobbies – fishing

  • Environmental – atmospheric deposition from coal-fired power plants, incineration of municipal and solid waste, latex paints, fish consumptions

  • Substance use – folk medicines, cosmetic; dental amalgams have not been proven to cause adverse effects.

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Mercury Health Effects

  • Effects depend on duration, intensity, and route of exposure, and chemical form

  • Central nervous system and kidneys are key targets

    • Elemental mercury: nervous system

    • Mercury salts: respiratory or GI (acute exposure); kidneys (chronic exposure)

    • Organic mercury: nervous system; developmental effects

  • Elemental mercury not classified with respect to carcinogenicity (USEPA Class D)

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Observed Effects of Methylmercury Toxicity

  • Iraq and Minamata (Japan)

  • Effects in utero quite different from childhood or adult exposures

  • Fetus is the most sensitive

  • Methylmercury exposed women have delivered infants with severe behavioral and sensory deficits, including deafness and blindness without maternal toxicity

  • Prenatal exposure results in a widespread pattern of adverse effects on brain development and organization

    • Alters the normal migration of neurons to cerebellar and cerebral cortices during brain development

    • Reduced brain size

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Mercury Controversy

  • Two recent studies of predominately fish eating populations:

    • Faroese Islands

      • Dose dependent relationship seen (delayed language, reduced memory and attention spans)

    • Seychelle Islands

      • No health effects observed

  • Many experts strongly advise pregnant women and women of child bearing age to limit exposure

  • However, fish is a significant source of protein throughout the world, some argue that the benefits outweigh the potential risk from low-level exposure

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Mercury Biological Fate

  • Chemical and physical form of mercury determine absorption, metabolism, distribution, and excretion pathways

    • Elemental mercury: nearly completely absorbed when inhaled; poorly absorbed when ingested or via dermal contact; readily crosses blood-brain barrier

    • Mercury salts: Mercuric Hg2+) salts are generally more soluble, and therefore more toxic than mercurous (Hg1+) salts; on average, less than 10% of ingested salts absorbed in GI tract; do not cross blood-brain barrier as readily

    • Organic mercury: readily absorbed by inhalation, dermal, contact, and ingestion; distributed uniformly to all tissues, although concentrated mostly in blood and brain.

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Mercury Standards and Regulations

Air Concentrations

OSHA – organic mercury PEL 0.1 mg/m3

metallic mercury vapor PEL 0.05 mg/m3

Water (inorganic mercury)

EPA – drinking water maximum contaminant level 2 ug/L

CAlEPA – drinking water public health goal 1.2 ug/L

CAlEPA – drinking water maximum contaminant level 2 ug/L


FDA – Fish action level 1 ppm

USEPA – fish action level 0.3 ppm

Japan – fish action level 0.3 ppm

Australia – fish action level 0.5 ppm

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California Proposition 65 Fish Lawsuit

  • Filed by Attorney General/TI January 2003

  • USFDA listed fish: swordfish, mackerel, tile fish, and shark

  • Safeway, Kroger, Albertsons, Trader Joe’s and Whole Foods

  • Dr. Katherine Mahaffey who wrote USEPA Mercury report to Congress and helped developed RfD says “ . . . other states are going to pick up the idea. Clearly it’s an important step.”

  • Red Lobster is next . . .

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  • Exposure Interviews

    • Occupation, housing (recent move), lifestyle/hobbies (fish consumption), school laboratory

  • Signs and Symptoms

    • Elemental mercury: pulmonary and CNS effects (cough, chest pain, colitis, pulmonary edema); chronic exposure may result in tremor and personality disorders

    • Mercury salts: affects GI tract and kidneys

    • Organic mercury: typically nonspecific and delayed (ataxia, malaise, blurred vision); chronic exposure may result in permanent CNS damage

  • Blood lead level typical test for acute exposure; urine test for chronic exposure

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Signs and Symptoms at Various Urine Mercury Levels

Sign and Symptoms Urine (ug/L)

Decreased response on tests for nerve condition, brain wave activity and verbal skills; early indication of tremor


Irritability, depression, memory loss, minor tremor, other nervous system disturbances; disturbed kidney function


Kidney inflammation, swollen gums, significant tremor and nervous system disturbances


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  • Depends on form of mercury exposure

  • Elemental mercury of mercury salts

    • Limit exposure

    • Chelation therapy

  • Organic mercury

    • No antidote; supportive care recommended

    • Chelating agent BAL contraindicated, as it has been shown to increase methylmercury concentrations in the brain