Mercury toxicity Mercury toxicity Dr shabeel pn
Mercury toxicityMercury toxicity
Dr shabeel pn
ObjectivesObjectives
Review the basic chemistry and biology of mercury in fish and humans
Review attempts to determine “safe” level of consumption of mercury (reference dose)
Present current risk advisories and discuss their impacts
Toxic PathwayToxic Pathway
ExposureAbsorptionDistributionBiotransformationElimination +/- Clinical Illness
Absorption of Toxic AgentAbsorption of Toxic Agent
Through IngestionThrough InhalationThrough SkinFrom the mother –
“transplacental”
Fetal ToxicityFetal Toxicity
Birth defects may be due to a brief exposure during critical periods of fetal development
Affected fetuses may spontaneously abortRelationship between exposure and
outcome is difficult to establish
Potential for Mercury ToxicityPotential for Mercury Toxicity
Elemental Mercury is “quicksilver”Mercury occurs naturally in soil and in the
atmosphere from volcanic emissionsMercury is extracted and used in industry,
then enters air or water from pollutionMercury was formerly used in some
medications causing direct exposure
Elemental MercuryElemental Mercury
Also referred to as “inorganic” mercury along with mercury salts
Very toxic to the nervous system, also to kidneys
But….very poorly absorbed by the GI tract so ingestion poses little risk
Inhalation route gives higher exposureMercury in fillings is inorganic
Toxicity of Organic MercuryToxicity of Organic Mercury
Mercury can be formulated as an organic compound with strong anti-microbial properties
Poisoning from diaper creams demonstrated dermal absorption and toxicity
the form of mercury with the most toxicity concerns
Organic Mercury PoisoningOrganic Mercury Poisoning
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
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
Iraq mercury contaminated seed grain – similar toxicity
MethylmercuryMethylmercury
Methylmercury (organic) is far more toxic than other forms and is well absorbed when ingested
It can be measured in blood and hairIt is very slowly eliminated, ½ life of 2 to
3 months
MethylmercuryMethylmercurySources of ExposureSources of Exposure
Elemental mercury is biotransformed by bacteria into methyl mercury and then the bacteria are eaten by mollusks, crustaceans etc.
Poorly eliminated so it concentrates up the food chain… Biggest and oldest predators at the top of the ecosystem have the highest concentrations
Methylmercury is distributed evenly throughout the fish and is not changed by cooking
Sources of MethylmercurySources of Methylmercury
Levels are higher in long-lived predator fishSome fish may have higher levels based on
regional environmental pollutionMany health departments issue health
advisories on consumption of “sport” fish Small fish, mollusks and crustaceans have
low levels unless in polluted waters
What Fish are Low in What Fish are Low in Mercury?Mercury?
Ocean fish are less likely to have industrial contamination than lake fish
Fish that are not predators Smaller, “Pan-sized” fishSalmon – (except large, lake salmon)Data is lacking on many species
Mercury Mercury How Much is Toxic?How Much is Toxic?
Two large prospective cohort studies of high fish eating populations
Both assessed mother/infant/child mercury levels from hair and blood and performed neurological testing over time
Mercury from Fish and Neurologic Mercury from Fish and Neurologic OutcomesOutcomes
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.
Adverse outcomes on some tests correlate with degree of mercury exposure
Mercury from Fish and Neurologic Mercury from Fish and Neurologic OutcomesOutcomes
Davidson PW, Effects of prenatal and postnatal mercury exposure from fish consumption on neurodevelopment: Seychelles Child Development Study. JAMA. 1998;280:701-707
No adverse neurologic effects on offspring related to level of mercury exposure
Mercury from Fish and Neurologic Mercury from Fish and Neurologic OutcomesOutcomes
Steurwald U, et al. Maternal seafood diet, methyl mercury exposure, and neonatal neurologic function. The Journal of Pediatrics. 2000;136:5:599-605.
Abnormalities in newborn exams correlated with high maternal mercury levels
Mercury from Fish and Neurologic Mercury from Fish and Neurologic OutcomesOutcomes
Conclusion: No “bright line” for safety Some believe risk is overstated:
Commercial Fish: Eat Up: despite low levels of mercury. http://www.rochester.edu/pr/releases/med/mercury.htm (9/2001)
Some believe government advisories are not strong enough
Mercury Mercury How Much is Toxic?How Much is Toxic?
National Academy of Sciences. Toxicologic effects of methylmercury. Washington, DC: National Research Council, 2000.
Reference Dose recommended to EPA is 0.1micrograms/kg/day
(“safe” daily intake to avoid toxicity)
Mercury Mercury How Much is Toxic?How Much is Toxic?
To follow EPA reference dose:– Fish with levels of 1 part per million
or greater should not be eaten at all– Fish with levels greater than 0.2 ppm
need to be limited to about once per week
Mercury Consumer WarningsMercury Consumer Warnings
January 2001, FDA recommends pregnant women, those who may be pregnant and children less than 5, not eat swordfish, shark, king mackerel and tilefish
Pregnant women should limit intake of all other types of fish to 12oz./week and eat a variety of fish
What Do We Know About Fish What Do We Know About Fish Consumption in Hawaii?Consumption in Hawaii?
Several epidemiologic dietary studies for cardiovascular and cancer risk have established that many people in Hawaii have high fish consumption
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
What do we know about MM What do we know about MM Levels in Hawaii Fish?Levels in Hawaii Fish?
DOH has data from 1991 demonstrating expected high levels in shark and swordfish
Other sampled fish included large tuna, marlin a few other species, levels often greater than 0.2ppm
National data is scarce or absent for many Hawaii fish
Hawaii FishHawaii Fish
Swordfish in Hawaii - Broadbill Swordfish – (Shutome, Au)
Shark Other Billfish – Blue and Stripped Marlin (Au,
Kajiki, Nairagi) Tuna – Big Eye, Yellow Fin, Skipjack (ahi, aku) Other predators Ono, Moonfish, Mahimahi,
Snappers, Groupers
Importance of Mercury Importance of Mercury ToxicityToxicity
Animal evidence and studies of special populations show reason for concern regarding methylmercury
Brain injury is still being demonstrated related to Minimata exposure
The source of many developmental deficits in children are unknown
Mercury Toxicity ControversyMercury Toxicity ControversyEating fish confers health benefitsIndividuals may manage mercury risk by
eating less healthy foodsRisk advisories aimed at pregnant women
affect other family membersDietary changes initiated during
pregnancy will have little effect on outcome
What are we Doing?What are we Doing?
WIC Fish Advisory BrochureLooking to define levels of commonly eaten
fish and establish fish with low levels“Translate” conservative RD approach for
Hawaii populationPromote “smarter fish eating”, not switch to
other foods
What are we Doing?What are we Doing?
Working with Fishing IndustryGather better data on mercury content of
fish eaten in HawaiiSampling of Hawaii fish underwayLooking at data sources for wholesale and
retail fish volumes
What are we Doing?What are we Doing?
Promote research:– Studies of women of child-bearing age
and cord blood to determine extent of exposure
– Outcome studies Looking for funding for studies
Other Issues for HawaiiOther Issues for Hawaii
Volcano’s contribution unknown – while volcanic emissions are an important natural source of mercury, ocean levels are not reported to be rising
Many biology questions related to how MM concentrates up the “food chain” remain unanswered
ResourcesResources
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)
Environmental Protection Agency: Mercury Update, Impact on Fish Advisories, June 2001. http://www.epa.gov/ost/fish/ (9/2001)
ResourcesResources
American Academy of Pediatrics. Technical Report: Mercury in the Environment: Implications for Pediatricians. Committee on Environmental Health. Pediatrics. 2001;108:1;197-205.
Agency for Toxic Substances and Disease Registry (ATSDR) – http://atsdr1.atsdr.cdc.gov:8080/child