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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

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

who s at risk
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
  • 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
sources of lead exposure ingestion and inhalation
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
nutrition and lead
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
lead health effects
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)
lead health effects cont
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
lead health effects cont d
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
lead biological fate
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
health effects at various blood lead levels
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

lead standards and regulations
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

poverty and lead poisoning
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
blood lead levels for various groups of people
Blood Lead Levels for Various Groups of People

Rural Children 7-11

Urban Children 9-33

Adults 15-22

Children near smelter 35-68

  • 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
  • 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


  • 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
sources of mercury exposure
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
sources of mercury exposure cont
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.
mercury health effects
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)
observed effects of methylmercury toxicity
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
mercury controversy
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
mercury biological fate
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.
mercury standards and regulations
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

california proposition 65 fish lawsuit
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 . . .
  • 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
signs and symptoms at various urine mercury levels
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


  • 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