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METHYLMERCURY IN FISH TOXICOLOGY & RISK CHARACTERIZATION. Air Toxics Workshop II June 12, 2007 Jerry Ann Ward, Ph.D. Department of State Health Services, Seafood and Aquatic Life Group Austin, Texas (512) 834-6757. ATMOSPHERIC DEPOSITION of INORGANIC Hg. Air-

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METHYLMERCURY IN FISH TOXICOLOGY & RISK CHARACTERIZATION


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methylmercury in fish toxicology risk characterization

METHYLMERCURY IN FISH TOXICOLOGY & RISK CHARACTERIZATION

Air Toxics Workshop II

June 12, 2007

Jerry Ann Ward, Ph.D.

Department of State Health Services,

Seafood and Aquatic Life Group

Austin, Texas

(512) 834-6757

atmospheric deposition of inorganic hg
ATMOSPHERIC DEPOSITION of INORGANIC Hg
  • Air-
    • A primary transport route of mercury to water:
    • Approximately 30% of Hg in air comes from natural sources
    • Up to 70% of Hg in air comes from human activities
  • Human Activities Known to Produce Airborne Hg
    • Coal fired power plants
    • Waste incinerators including medical, Hazardous, and Household
    • Mercury cell chlorine manufacturing facilities
    • Other anthropogenic sources
hg to methylmercury critical connection between airborne hg methylmercury in fish
Hg to METHYLMERCURY –Critical Connection between Airborne Hg & Methylmercury in Fish
  • Methylmercury produced by microorganisms in water from elemental mercury and/or inorganic salts of mercury
    • Natural Process
    • A Part of the Environmental Hg Cycle
  • Waters with high levels of organic matter and acidic pH likely to have microorganisms to convert inorganic mercury to methylmercury, the organic salt of most concern.
hg to methylmercury critical connection between airborne hg methylmercury in fish5
Hg to METHYLMERCURY –Critical Connection between Airborne Hg & Methylmercury in Fish
  • Hg falls enters water, runs off land, or is otherwise deposited into water boy, where micro-organisms’ enzymes convert inorganic Hg to methylmercury (MeHg)
  • Water conditions conducive to conversion:
    • high levels of organic matter
    • acidic pH
hg to methylmercury critical connection between airborne hg methylmercury in fish6
Hg to METHYLMERCURY –Critical Connection between Airborne Hg & Methylmercury in Fish
  • Plankton, other small organisms obtain MeHg
  • Bottom-feeding fish eat plankton, often concentrating MeHg (bio-concentration)
  • Mid-trophic level fish eat bottom dwellers, retaining MeHg in process (bio-concentration)
  • Higher-trophic level fish consume midlevel to top-level predatory fish that, then get MeHg from their food source as well as from water, magnifying amount of MeHg in top-level fish (bio-magnification)
  • People eat fish getting varying levels
characteristics of methylmercury in water
Characteristics of Methylmercury in Water
  • Concentrations in water are thus many times lower in water than in fish
  • Water usually poses no serious risk to health because levels are usually so low as to be un-measurable even in waters supporting fish with very high levels of MeHg in fish
methylmercury in fish is of concern to human health because
Methylmercury in fish is of concern to human health because:
  • Consumption of contaminated fish is the only significant source of human exposure to methylmercury
  • At lowest doses, methylmercury may be
    • Toxic to fetal CNS (Controversial).
characteristics of methylmercury in fish
Characteristics of Methylmercury in Fish
  • Persistent – most fish have no metabolic pathways by which to rid their bodies of MeHg
  • Bio-accumulates in aquatic organisms-highest levels in long-lived, predatory fish-
  • Concentrations in fish can be tens of thousands times higher than concentration in surrounding waters.
characteristics of methylmercury in human beings
Bioaccumulation in humans who consume methylmercury-contaminated fish.

Humans may detoxify methylmercury. Biological T1/2 in humans is approximately 70 days.

Characteristics of Methylmercury in Human Beings
health effects of methylmercury
Health Effects of Methylmercury
  • Low-dose exposure
    • Adults
      • No known serious effects
characteristics of methylmercury in humans continued
Characteristics of Methylmercury in Humans, continued
  • Acute and Chronic Toxicity at high levels-almost All humans
symptoms of acute high level methylmercury intoxication in adults or children not minamata disease
Symptoms of Acute High Level Methylmercury Intoxication in Adults or Children (Not Minamata Disease)
  • Numbness and tingling skin usually follows dermatomes
  • Loss of coordination
  • Visual and hearing impairment
  • Slurred speech
  • Death or permanent disability
slide15
Acute toxicity to fetus at low-levels and/or with long-term exposure
  • Fetuses exposed to large doses of methylmercury ( 125 ug/L maternal blood) may be born with “Fetal Minamata Disease” a disorder characterized by:
    • Mental retardation
    • Cerebral palsy
    • Seizures
    • Abnormal reflexes
    • Dysarthria - disturbance of speech due to brain injury or paralysis or spasticity of muscles of speech
health effects of low dose long term fetal exposure to mehg
Health Effects of Low Dose, long –term fetal exposure to MeHg

Neurotoxicity – subtle

  • Poor performance on neurobehavioral tests
  • Attention deficits
  • Fine motor deficits
  • Language deficits
  • Visual-spatial dysfunction
  • Verbal memory deficits
legislative authority
Legislative Authority
  • Health and Safety Code, Section 436.003 et seq. The commissioner by order shall declare any public water to be a prohibited area if. . . area contains aquatic life that is unfit for human consumption
risk assessment components
Risk Assessment Components
  • Problem Identification
  • Toxicity Assessment
  • Receptor Characterization
  • Exposure Assessment
  • Risk Characterization
  • Risk Management
identify problem methylmercury
IDENTIFY PROBLEM(Methylmercury)
  • Select water body and target species: Likely present in high-trophic level, older, leaner fish
  • Obtain samples of target species
  • Analyze tissue from target species for total mercury
  • Determine concentration of mercury: total mercury concentration assumed to equal methylmercury in tissue (mg/kg)
characterize receptor s
CHARACTERIZE RECEPTOR(s)
  • Population at Risk: Humans Sensitive Sub-groups
      • FETUS-via pregnant women, women who may become pregnant
      • Cross-placental
      • INFANT?-via nursing mothers or direct consumption at early age
characterize receptor humans
CHARACTERIZE RECEPTOR (humans)
  • ADOLESCENT and ADULT MALES, WOMEN WHO CANNOT BEAR CHILDREN
      • Low level exposure-likely no visible or long-term effects
      • High level exposure-likely visible, acute toxicity
assess toxicity of methylmercury
ASSESS TOXICITY of METHYLMERCURY
  • Health-based Comparison Values (HACs)
  • Systemic toxicity
    • RfD x BW ÷ Consumption Rate
    • 0.0003 X 70 ÷0.030 = 0.7 mg/kg tissue
  • Cancer – not an issue with MeHg
produce risk characterization report
PRODUCE RISK CHARACTERIZATION REPORT
  • Introduction and Statement of the Problem
  • Materials and Methods
  • Results
  • Discussion
    • Conclusions
    • Recommendations for reducing exposure-
    • Communication of Health Risk to Public
risk management
RISK MANAGEMENT
  • Decision-making process used to:
    • Develop, analyze, and compare regulatory options
    • Select appropriate regulatory responses to a potential or current public health hazard