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Health Effects of Mercury Exposure

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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Health Effects of Mercury Exposure

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  1. Health Effects of Mercury Exposure Victoria Persky, M.D.

  2. Overview • Exposures • Health Effects • Prevention Strategies

  3. 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

  4. Sources of Environmental Mercury: Natural (6-59% U.S.) • Outgasing of the earth’s crust • Water • Vegetation surfaces • Wild fires; volcanoes • Geothermal

  5. Industrial Sources Mercury • Electrolytic production in chloralkali plants • Amalgamation in gold production • Manufacture of electrical equipment • Coal fired power plants • Steel production

  6. 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

  7. 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)

  8. Hylander: The Science of the Total Environment 2003; 304: 13-27

  9. Environmental Mercury • Atmospheric increased 20-fold since pre-industrial time • Peak production 8000 tons/year 1961-1970 • Current production <2000 tons/year

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. Mercury Spills • Broken thermometers • Chemistry laboratories • Removal gas regulators

  16. 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)

  17. 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

  18. 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

  19. Neurodevelopmental Cognitive Auditory Visual Cerebellar Fine Motor Cardiovascular Decreased heart rate variability Hypertension Myocardial infarction Sudden death Health Effects of Methylmercury

  20. 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)

  21. 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

  22. 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

  23. 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)

  24. Blood Mercury Levels: NHANES, 1999-2000 Mahaffey EHP 112: 562-570, 2004

  25. 31 Great Lake Sport Fish ConsumersMetals in Blood (mean)

  26. Blood Levels in 32 Great Lakes Sports Fishermen, 1993 Anderson EHP 106: 279-289, 1998

  27. PCB Mean Congener SumExposure Group by Lake (N=438)

  28. 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

  29. Reduction Exposures • Protected stockpiles • Alternative uses (thermometers/dental) • Reduction power plants • Decreased use of coal • Pretreatment coal thermal/acid wash • Desulphurization

  30. 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

  31. 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

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