METHYLMERCURY IN FISH TOXICOLOGY

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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
• [phone]

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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

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Reported Hg Concentrations in Air Across the U.S.
compared to Texas and Harris County, 2000-2006
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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.

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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

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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

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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

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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).

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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.

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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.

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Health Effects of Methylmercury

• Low-dose exposure
• Adults
• No known serious effects

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Characteristics of Methylmercury in Humans,
continued

• Acute and Chronic Toxicity at high levels-almost
  All humans

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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

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High Dose MeHg-Fetus
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• 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

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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

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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

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Risk Assessment Components

• Problem Identification
• Toxicity Assessment
• Receptor Characterization
• Exposure Assessment
• Risk Characterization
• Risk Management

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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)

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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

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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

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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

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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

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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

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Questions?