Mercury Toxicity

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Mercury Toxicity

  1. 1. Mercury toxicity Dr shabeel pn
  2. 2. Objectives <ul><li>Review the basic chemistry and biology of mercury in fish and humans </li></ul><ul><li>Review attempts to determine “safe” level of consumption of mercury (reference dose) </li></ul><ul><li>Present current risk advisories and discuss their impacts </li></ul>
  3. 3. Toxic Pathway <ul><li>Exposure </li></ul><ul><li>Absorption </li></ul><ul><li>Distribution </li></ul><ul><li>Biotransformation </li></ul><ul><li>Elimination </li></ul><ul><li>+/- Clinical Illness </li></ul>
  4. 4. Absorption of Toxic Agent <ul><li>Through Ingestion </li></ul><ul><li>Through Inhalation </li></ul><ul><li>Through Skin </li></ul><ul><li>From the mother – “transplacental” </li></ul>
  5. 5. Fetal Toxicity <ul><li>Birth defects may be due to a brief exposure during critical periods of fetal development </li></ul><ul><li>Affected fetuses may spontaneously abort </li></ul><ul><li>Relationship between exposure and outcome is difficult to establish </li></ul>
  6. 6. Potential for Mercury Toxicity <ul><li>Elemental Mercury is “quicksilver” </li></ul><ul><li>Mercury occurs naturally in soil and in the atmosphere from volcanic emissions </li></ul><ul><li>Mercury is extracted and used in industry, then enters air or water from pollution </li></ul><ul><li>Mercury was formerly used in some medications causing direct exposure </li></ul>
  7. 7. Elemental Mercury <ul><li>Also referred to as “inorganic” mercury along with mercury salts </li></ul><ul><li>Very toxic to the nervous system, also to kidneys </li></ul><ul><li>But…. very poorly absorbed by the GI tract so ingestion poses little risk </li></ul><ul><li>Inhalation route gives higher exposure </li></ul><ul><li>Mercury in fillings is inorganic </li></ul>
  8. 8. Toxicity of Organic Mercury <ul><li>Mercury can be formulated as an organic compound with strong anti-microbial properties </li></ul><ul><li>Poisoning from diaper creams demonstrated dermal absorption and toxicity </li></ul><ul><li>the form of mercury with the most toxicity concerns </li></ul>
  9. 9. Organic Mercury Poisoning <ul><li>Minimata, Japan, 50 years ago…Seafood from the bay was polluted with mercury from an industrial source, many cases of neurotoxcity were seen, directly related to seafood consumption </li></ul><ul><li>Most striking was the vulnerability of the fetal brain to mercury toxicity shown by the high rate of cerebral palsy in children born during this period </li></ul><ul><li>Iraq mercury contaminated seed grain – similar toxicity </li></ul>
  10. 10. Methylmercury <ul><li>Methylmercury (organic) is far more toxic than other forms and is well absorbed when ingested </li></ul><ul><li>It can be measured in blood and hair </li></ul><ul><li>It is very slowly eliminated, ½ life of 2 to 3 months </li></ul>
  11. 11. Methylmercury Sources of Exposure <ul><li>Elemental mercury is biotransformed by bacteria into methyl mercury and then the bacteria are eaten by mollusks, crustaceans etc. </li></ul><ul><li>Poorly eliminated so it concentrates up the food chain… Biggest and oldest predators at the top of the ecosystem have the highest concentrations </li></ul><ul><li>Methylmercury is distributed evenly throughout the fish and is not changed by cooking </li></ul>
  12. 12. Sources of Methylmercury <ul><li>Levels are higher in long-lived predator fish </li></ul><ul><li>Some fish may have higher levels based on regional environmental pollution </li></ul><ul><li>Many health departments issue health advisories on consumption of “sport” fish </li></ul><ul><li>Small fish, mollusks and crustaceans have low levels unless in polluted waters </li></ul>
  13. 13. What Fish are Low in Mercury? <ul><li>Ocean fish are less likely to have industrial contamination than lake fish </li></ul><ul><li>Fish that are not predators </li></ul><ul><li>Smaller, “Pan-sized” fish </li></ul><ul><li>Salmon – (except large, lake salmon) </li></ul><ul><li>Data is lacking on many species </li></ul>
  14. 14. Mercury How Much is Toxic? <ul><li>Two large prospective cohort studies of high fish eating populations </li></ul><ul><li>Both assessed mother/infant/child mercury levels from hair and blood and performed neurological testing over time </li></ul>
  15. 15. Mercury from Fish and Neurologic Outcomes <ul><li>Faroe Islands, Grandjean P, et al. Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury. Neurotoxicology and Teratology. 1997;19:417-428. </li></ul><ul><li>Adverse outcomes on some tests correlate with degree of mercury exposure </li></ul>
  16. 16. Mercury from Fish and Neurologic Outcomes <ul><li>Davidson PW, Effects of prenatal and postnatal mercury exposure from fish consumption on neurodevelopment: Seychelles Child Development Study. JAMA. 1998;280:701-707 </li></ul><ul><li>No adverse neurologic effects on offspring related to level of mercury exposure </li></ul>
  17. 17. Mercury from Fish and Neurologic Outcomes <ul><li>Steurwald U, et al. Maternal seafood diet, methyl mercury exposure, and neonatal neurologic function. The Journal of Pediatrics. 2000;136:5:599-605. </li></ul><ul><li>Abnormalities in newborn exams correlated with high maternal mercury levels </li></ul>
  18. 18. Mercury from Fish and Neurologic Outcomes <ul><li>Conclusion: No “bright line” for safety </li></ul><ul><li>Some believe risk is overstated: </li></ul><ul><li>Commercial Fish: Eat Up: despite low levels of mercury. http://www.rochester.edu/pr/releases/med/mercury.htm (9/2001) </li></ul><ul><li>Some believe government advisories are not strong enough </li></ul>
  19. 19. Mercury How Much is Toxic? <ul><li>National Academy of Sciences. Toxicologic effects of methylmercury. Washington, DC: National Research Council, 2000. </li></ul><ul><li>Reference Dose recommended to EPA is 0.1micrograms/kg/day </li></ul><ul><li>(“safe” daily intake to avoid toxicity) </li></ul>
  20. 20. Mercury How Much is Toxic? <ul><li>To follow EPA reference dose: </li></ul><ul><ul><li>Fish with levels of 1 part per million or greater should not be eaten at all </li></ul></ul><ul><ul><li>Fish with levels greater than 0.2 ppm need to be limited to about once per week </li></ul></ul>
  21. 21. Mercury Consumer Warnings <ul><li>January 2001, FDA recommends pregnant women, those who may be pregnant and children less than 5, not eat swordfish, shark, king mackerel and tilefish </li></ul><ul><li>Pregnant women should limit intake of all other types of fish to 12oz./week and eat a variety of fish </li></ul>
  22. 22. What Do We Know About Fish Consumption in Hawaii? <ul><li>Several epidemiologic dietary studies for cardiovascular and cancer risk have established that many people in Hawaii have high fish consumption </li></ul><ul><li>Pilot testing of risk advisories through WIC program show many Hawaii women eat fish more than once a week, and eat varieties of fish with higher levels of mercury </li></ul>
  23. 23. What do we know about MM Levels in Hawaii Fish? <ul><li>DOH has data from 1991 demonstrating expected high levels in shark and swordfish </li></ul><ul><li>Other sampled fish included large tuna, marlin a few other species, levels often greater than 0.2ppm </li></ul><ul><li>National data is scarce or absent for many Hawaii fish </li></ul>
  24. 24. Hawaii Fish <ul><li>Swordfish in Hawaii - Broadbill Swordfish – (Shutome, Au) </li></ul><ul><li>Shark </li></ul><ul><li>Other Billfish – Blue and Stripped Marlin (Au, Kajiki, Nairagi) </li></ul><ul><li>Tuna – Big Eye, Yellow Fin, Skipjack (ahi, aku) </li></ul><ul><li>Other predators Ono, Moonfish, Mahimahi, Snappers, Groupers </li></ul>
  25. 25. Importance of Mercury Toxicity <ul><li>Animal evidence and studies of special populations show reason for concern regarding methylmercury </li></ul><ul><li>Brain injury is still being demonstrated related to Minimata exposure </li></ul><ul><li>The source of many developmental deficits in children are unknown </li></ul>
  26. 26. Mercury Toxicity Controversy <ul><li>Eating fish confers health benefits </li></ul><ul><li>Individuals may manage mercury risk by eating less healthy foods </li></ul><ul><li>Risk advisories aimed at pregnant women affect other family members </li></ul><ul><li>Dietary changes initiated during pregnancy will have little effect on outcome </li></ul>
  27. 27. What are we Doing? <ul><li>WIC Fish Advisory Brochure </li></ul><ul><li>Looking to define levels of commonly eaten fish and establish fish with low levels </li></ul><ul><li>“Translate” conservative RD approach for Hawaii population </li></ul><ul><li>Promote “smarter fish eating”, not switch to other foods </li></ul>
  28. 28. What are we Doing? <ul><li>Working with Fishing Industry </li></ul><ul><li>Gather better data on mercury content of fish eaten in Hawaii </li></ul><ul><li>Sampling of Hawaii fish underway </li></ul><ul><li>Looking at data sources for wholesale and retail fish volumes </li></ul>
  29. 29. What are we Doing? <ul><li>Promote research: </li></ul><ul><ul><li>Studies of women of child-bearing age and cord blood to determine extent of exposure </li></ul></ul><ul><ul><li>Outcome studies </li></ul></ul><ul><li>Looking for funding for studies </li></ul>
  30. 30. Other Issues for Hawaii <ul><li>Volcano’s contribution unknown – while volcanic emissions are an important natural source of mercury, ocean levels are not reported to be rising </li></ul><ul><li>Many biology questions related to how MM concentrates up the “food chain” remain unanswered </li></ul>
  31. 31. Resources <ul><li>Federal Drug Administration: An important message for pregnant women and women of childbearing age who may become pregnant about the risk of mercury in fish. March 2001. http://www.cfsan.fda.gov/~dms/admehg.html (9/2001) </li></ul><ul><li>Environmental Protection Agency: Mercury Update, Impact on Fish Advisories, June 2001. http://www.epa.gov/ost/fish/ (9/2001) </li></ul>
  32. 32. Resources <ul><li>American Academy of Pediatrics. Technical Report: Mercury in the Environment: Implications for Pediatricians. Committee on Environmental Health. Pediatrics. 2001;108:1;197-205. </li></ul><ul><li>Agency for Toxic Substances and Disease Registry (ATSDR) – http://atsdr1.atsdr.cdc.gov:8080/child </li></ul>

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