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Health Effects of Mercury Exposure . Victoria Persky, M.D. Overview. Exposures Health Effects Prevention Strategies. Forms of Mercury. Elemental Hg 0 – liquid at room temperature; equilibrates with air

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overview
Overview
  • Exposures
  • Health Effects
  • Prevention Strategies
forms of mercury
Forms of Mercury
  • Elemental Hg0 – liquid at room temperature; equilibrates with air
  • Inorganic compounds – mercurous chloride (Hg2Cl2 camomel); mercuric fulminate (HgOCN2 detonator); mercuric sulfide (HgS paint pigment)
  • Organic mercury derives from divalent Hg2+ from bacteria in water bodies: methylmercury in fish; ethylmercury in thimerosal vaccines
sources of environmental mercury natural 6 59 u s
Sources of Environmental Mercury: Natural (6-59% U.S.)
  • Outgasing of the earth’s crust
  • Water
  • Vegetation surfaces
  • Wild fires; volcanoes
  • Geothermal
industrial sources mercury
Industrial Sources Mercury
  • Electrolytic production in chloralkali plants
  • Amalgamation in gold production
  • Manufacture of electrical equipment
  • Coal fired power plants
  • Steel production
u s anthropogenic sources
U.S. Anthropogenic Sources
  • In 1994, U.S. coal-fired utilities released approximately 51 tons per year of Hg
  • This is 33% of the estimated 158 tons per year of all airborne anthropogenic emissions of Hg in U.S.
  • U.S. anthropogenic emissions account for 3% of global total
  • U.S. utilities account for 1% of global total
hg transport from utility sources
Hg Transport from Utility Sources
  • 1/3 (52 tons) deposited within lower 48 states
  • 2/3 (107 tons) transported outside U.S. borders and contributes to global reservoir
  • Illinois utilities emit about 3 tons of Hg per year (4th largest state total)
environmental mercury
Environmental Mercury
  • Atmospheric increased 20-fold since pre-industrial time
  • Peak production 8000 tons/year 1961-1970
  • Current production <2000 tons/year
measurement issues
Measurement Issues
  • Organic methyl mercury - most mercury exposure in general population from fish – measured in blood, hair, toenails
  • Inorganic -elemental mercury exposure less common except in selected situations (chemistry labs, dental, thermometers, folk medicines, gas meters) – measured in urine
  • Mercury exposure in general population ultimately from industrial sources with wide distribution and bioaccumulates in food chain
sensitive populations
Sensitive Populations
  • Children
    • Mercury vapors heavy and settle on floor where children play
    • Blood brain barrier children more permeable
    • Respiration rate higher
    • Nervous system still developing
sensitive populations cont
Sensitive Populations (Cont)
  • Gender differences antioxidant protection and metabolism
  • Genetic polymorphism in coproporphyrinogen oxidase (CPOX4) affects neurobehavior

Vahter M et al Environ Res 2006; Echeverria D et al Neurotoxicology and Teratology 28: 39-48, 2006

current issues other forms mercury exposure
Current Issues Other Forms Mercury Exposure
  • Ethylmercury – thimerosal vaccines controversial; no conclusive health effect
  • Dental amalgams – some evidence that number of amalgams mother related to child’s exposure – no conclusive health effects
  • Inorganic mercury – powders and creams
  • Accidental spills elemental mercury
  • Ritual use of mercury
health effect elemental inorganic mercury
Health Effect Elemental/Inorganic Mercury
  • Chemical pneumonitis
  • Acrodynia (hypersensitivity rash palms,soles, face)
  • Insomnia
  • Tremor
  • Excitability
  • Incoordination
  • Memory loss
  • Decreased nerve conduction
  • Delirium (mad as a hatter)
  • Renal
mercury spills
Mercury Spills
  • Broken thermometers
  • Chemistry laboratories
  • Removal gas regulators
removal gas regulators illinois
Removal Gas Regulators Illinois
  • June 2000 meter/regulator removed July father noted mercury (78 μg/m3 staircase to basement); son had blood mercury level 16 μ24-hour urine of 25 μg/L (fell to <10 μg/L four months after removal)
  • Total of 360,000 homes screened, 1,363 contaminated, and 1,088 remediated. Overall risk of contamination 0.9-4.3/1,000 homes

Hryhorczuk et al EHP 114: 848-852,, 2006)

dental amalgams
Dental Amalgams
  • Positive correlations number of fillings and levels in urine, blood and tissue of mercury
  • Dentists have higher levels than general population
  • Inconsistent results with associations in dentists with memory, motor coordination and mood
  • Two recent trials in children with mercury vs resin found no significant differences in neurobehavioral, nerve conduction velocity or IQ

Bellinger et al JAMA 295: 1775-1783, 2006; DeRouen et al JAMA 295: 1784-1792, 2006

health effects thimerosal in vaccines
Health Effects Thimerosal in Vaccines
  • Used in vaccines in U.S. from 1930s to late 1990s
  • In July 1999 American Academy Pediatrics recommended removal from vaccines in U.S.
  • Inconsistent findings relating thimerosal exposure with health effects
    • ALSPAC Study: no consistent difference found
    • Retrospective cohort study with two HMO databases: a few associations seen for tics and language delay in the first database were not duplicated in the second cohort

Heron et al Pediatrics 114: 577-83, 2004; Verstraeten et al Pediatrics 112: 1039-48, 2003

health effects of methylmercury
Neurodevelopmental

Cognitive

Auditory

Visual

Cerebellar

Fine Motor

Cardiovascular

Decreased heart rate variability

Hypertension

Myocardial infarction

Sudden death

Health Effects of Methylmercury
early studies
Early Studies
  • 1950s Minamata, Japan: industrial discharges through ingestion of contaminated fish – 2,000-12,000 cases; 100-800 deaths (Hylander Science of Total Environment 2006; 368:352-370)
  • 1972 Iraq: ingestion of bread made from contaminated seeds: 6,530 cases, 459 deaths (Bakir Science181: 230-241, 1973)
large cohort studies of neurodevelopmental effects
Large Cohort Studies of Neurodevelopmental Effects
  • Faroe Islands – cohort of 1022 consecutive births in 1986-87 followed 7 and 14 years; mixed exposure of Hg and PCBs
  • Seychelles Child Development Study – cohort of 779 mother child pairs in 1989-90 when children 6 months old through 9 years of age; exposure to fish containing Hg at US levels but 12 meals/week
results faroe islands and seychelles
Results Faroe Islands and Seychelles
  • Faroe Islands: Cord blood related to deficits in language attention, memory 7 yrs; increased BP 7 yrs, decreased HR variability 7 and 14 yrs, decreased auditory evoked potential 7 and 14 yrs
  • Seychelles: Mother’s hair Hg related to decreased performance pegboard grooved; no difference other tests

Grandjean: Amer J Epidemiol 150: 301-5, 1999; Neurotoxicol Teratol 23: 305-17, 2001, Neurotoxicol Teratol 19: 417-28, 1997, J Pediatr 144: 169-76, 2004; Sorenson Epidemiol 10:370-75, 1999; Murata J Pediatr 1444: 177-83, 2004 ; Myers Lancet 361: 1698-92, 2003

fish and chd
Fish and CHD
  • Western Electric: Inverse Associationfish intake with CHD(Daviglus N Engl J Med 336: 1046-53, 1997)
  • Male health professionals: Dentists had higher mercury (0.91 vs 0.45 ug/g); mercury related to fish intake (0.29 to 0.75 ug/g). No relationship mercury with CHD adjusting for n-3 fatty acids(Yoshizawa et al New Eng J Med 347: 1755-60, 2002)
  • Men with first MI and controls: Toenail Hg positively and adipose tissue docosahexaenoic acid inversely associated with MI(Guallar N Engl J Med 347: 1747-54, 2002)
  • Men Finland – High mercury hair 1.60 increased risk coronary event – protective effect docohexaenoic acid(Virtanen Artherioscler Thromb Vasc Biol 25: 228-33, 2005)
blood mercury levels nhanes 1999 2000
Blood Mercury Levels: NHANES, 1999-2000

Mahaffey EHP 112: 562-570, 2004

national research council 2000 recommendations
National Research Council 2000 Recommendations
  • Benchmark 58ug/l mercury cord blood – lower 95% CI Faroe islands that would result in doubling proportion children with abnormal developmental score
  • To account for uncertainty 10 fold less for 5.8 ug/l - currently estimate is that 7.8% potentially pregnant women above this dose assuming 1:1 maternal:cord blood – could be underestimate if maternal:cord is 1:1.7
  • Recent recommendations for potentially pregnant women no more than 2 fish meals a week and no ingestion of shark, swordfish, tile, king mackerel
reduction exposures
Reduction Exposures
  • Protected stockpiles
  • Alternative uses (thermometers/dental)
  • Reduction power plants
    • Decreased use of coal
    • Pretreatment coal thermal/acid wash
    • Desulphurization
power plant reductions
Power Plant Reductions
  • Federal EPA March 2005 required states to adopt rules to reduce Hg by 70% by 2018
  • Illinois Pollution Control Board in 2007 finalized requirements that power plants reduce Hg emissions Illinois 90% by 2009 or, if they adopt measures that address multi-pollutant reduction, reduce Hg emission 90% by 2015
conclusions
Conclusions
  • Health effects at current levels of exposure in population multifaceted with most evidence for neurodevelopmental and cardiovascular
  • Current prevention strategy limits intake of selected fish in high risk populations
  • Additional prevention strategies focus on alternative technologies, contained stockpiles, reduced discharges from industrial sources