METHYLMERCURY IN FISHMETHYLMERCURY IN FISH TOXICOLOGY & RISK TOXICOLOGY & RISK

CHARACTERIZATIONCHARACTERIZATION

Air Toxics Workshop IIAir Toxics Workshop IIJune 12, 2007June 12, 2007

Jerry Ann Ward, Ph.D.Jerry Ann Ward, Ph.D.Department of State Health Services,Department of State Health Services,

Seafood and Aquatic Life Group Seafood and Aquatic Life Group Austin, TexasAustin, Texas

(512) 834-6757(512) 834-6757

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ATMOSPHERIC DEPOSITION of ATMOSPHERIC DEPOSITION of INORGANIC HgINORGANIC Hg

• Air-Air-– A primary transport route of mercury to water: A primary transport route of mercury to water: – Approximately 30% of Hg in air comes from natural Approximately 30% of Hg in air comes from natural

sourcessources

– Up to 70% of Hg in air comes from human activitiesUp to 70% of Hg in air comes from human activities

• Human Activities Known to Produce Airborne Human Activities Known to Produce Airborne HgHg– Coal fired power plantsCoal fired power plants– Waste incinerators including medical, Hazardous, and Waste incinerators including medical, Hazardous, and

HouseholdHousehold– Mercury cell chlorine manufacturing facilitiesMercury cell chlorine manufacturing facilities– Other anthropogenic sourcesOther anthropogenic sources

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Reported Hg Concentrations in Air Reported Hg Concentrations in Air Across the U.S. compared to Across the U.S. compared to Texas and Harris County, 2000-Texas and Harris County, 2000-20062006

0.0

0.5

1.0

1.5

2.0

2.5

3.0

2000 2001 2002 2003 2004 2005 2006

Year Measured

USTexasHarris Co

Mer

cury

(PM

2.5

) C

once

ntr

atio

n

(Ng/M

3

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Hg to METHYLMERCURY –Critical Hg to METHYLMERCURY –Critical Connection between Airborne Hg Connection between Airborne Hg & Methylmercury in Fish& Methylmercury in Fish

Methylmercury produced by microorganisms in water Methylmercury produced by microorganisms in water

from elemental mercury and/or inorganic salts of mercuryfrom elemental mercury and/or inorganic salts of mercury

Natural Process Natural Process A Part of the Environmental Hg CycleA Part of the Environmental Hg Cycle

Waters with high levels of organic matter and acidic pH Waters with high levels of organic matter and acidic pH

likely to have microorganisms to convert inorganic likely to have microorganisms to convert inorganic

mercury to methylmercury, the organic salt of most mercury to methylmercury, the organic salt of most

concernconcern. .

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Hg to METHYLMERCURY –Critical Hg to METHYLMERCURY –Critical Connection between Airborne Hg Connection between Airborne Hg & Methylmercury in Fish& Methylmercury in Fish

Hg falls enters water, runs off land, or is Hg falls enters water, runs off land, or is

otherwise deposited into water boy, where otherwise deposited into water boy, where

micro-organisms’ enzymes convert micro-organisms’ enzymes convert

inorganic Hg to methylmercury (MeHg)inorganic Hg to methylmercury (MeHg)

Water conditions conducive to conversion:Water conditions conducive to conversion: high levels of organic matter high levels of organic matter acidic pHacidic pH

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Hg to METHYLMERCURY –Critical Hg to METHYLMERCURY –Critical Connection between Airborne Hg Connection between Airborne Hg & Methylmercury in Fish& Methylmercury in Fish

Plankton, other small organisms obtain MeHgPlankton, other small organisms obtain MeHg Bottom-feeding fish eat plankton, often Bottom-feeding fish eat plankton, often

concentrating MeHg (bio-concentration)concentrating MeHg (bio-concentration) Mid-trophic level fish eat bottom dwellers, retaining Mid-trophic level fish eat bottom dwellers, retaining

MeHg in process (bio-concentration)MeHg in process (bio-concentration) Higher-trophic level fish consume midlevel to top-Higher-trophic level fish consume midlevel to top-

level predatory fish that, then get MeHg from their level predatory fish that, then get MeHg from their

food source as well as from water, magnifying food source as well as from water, magnifying

amount of MeHg in top-level fish (bio-magnification)amount of MeHg in top-level fish (bio-magnification) People eat fish getting varying levels People eat fish getting varying levels

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Characteristics of Characteristics of Methylmercury in WaterMethylmercury in Water

• Concentrations in water are thus Concentrations in water are thus many times lower in water than many times lower in water than in fish in fish

• Water usually poses no serious Water usually poses no serious risk to health because levels are risk to health because levels are usually so low as to be un-usually so low as to be un-measurable even in waters measurable even in waters supporting fish with very high supporting fish with very high levels of MeHg in fish levels of MeHg in fish

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Methylmercury in fish is of Methylmercury in fish is of concern to human health concern to human health because:because:

Consumption of contaminated fish is Consumption of contaminated fish is the the only only significant source of human significant source of human exposure to methylmercuryexposure to methylmercury

At lowest doses, methylmercury may At lowest doses, methylmercury may bebe

– Toxic to fetal CNS (Controversial).Toxic to fetal CNS (Controversial).

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Characteristics of Methylmercury Characteristics of Methylmercury in Fish in Fish Persistent – most fish have no metabolic Persistent – most fish have no metabolic

pathways by which to rid their bodies of pathways by which to rid their bodies of MeHgMeHg

Bio-accumulates in aquatic organisms-Bio-accumulates in aquatic organisms-highest levels in long-lived, predatory fish-highest levels in long-lived, predatory fish-

Concentrations in fish can be tens of Concentrations in fish can be tens of thousands times higher than thousands times higher than concentration in surrounding waters. concentration in surrounding waters.

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Characteristics of Characteristics of Methylmercury in Human Methylmercury in Human BeingsBeings

Bioaccumulation in humans who Bioaccumulation in humans who consume methylmercury-consume methylmercury-contaminated fish.contaminated fish.

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

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Health Effects of Health Effects of Methylmercury Methylmercury

•Low-dose exposureLow-dose exposure– AdultsAdults

•No known serious effectsNo known serious effects

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Characteristics of Characteristics of Methylmercury in Humans, Methylmercury in Humans, continuedcontinued Acute and Chronic Toxicity at Acute and Chronic Toxicity at

high levels-almost All humanshigh levels-almost All humans

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Symptoms of Acute High Level Symptoms of Acute High Level Methylmercury Intoxication in Methylmercury Intoxication in Adults or Children (Not Minamata Adults or Children (Not Minamata

Disease)Disease)

• Numbness and tingling skin usually follows Numbness and tingling skin usually follows

dermatomesdermatomes

• Loss of coordinationLoss of coordination

• Visual and hearing impairmentVisual and hearing impairment

• Slurred speechSlurred speech

• Death or permanent disabilityDeath or permanent disability

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High Dose MeHg-FetusHigh Dose MeHg-Fetus

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Acute toxicity to fetus at low-levels and/or Acute toxicity to fetus at low-levels and/or with long-term exposure with long-term exposure

Fetuses exposed to large doses of Fetuses exposed to large doses of methylmercury (methylmercury ( 125 ug/L maternal 125 ug/L maternal blood) may be born with “Fetal blood) may be born with “Fetal Minamata Disease” a disorder Minamata Disease” a disorder characterized by: characterized by: Mental retardationMental retardation Cerebral palsyCerebral palsy SeizuresSeizures Abnormal reflexesAbnormal reflexes Dysarthria - disturbance of speech due to brain Dysarthria - disturbance of speech due to brain

injury or paralysis or spasticity of muscles of speechinjury or paralysis or spasticity of muscles of speech

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Health Effects of Low Dose, Health Effects of Low Dose, long –term fetal exposure to long –term fetal exposure to MeHgMeHg

Neurotoxicity – subtle Neurotoxicity – subtle – Poor performance on neurobehavioral Poor performance on neurobehavioral

teststests– Attention deficitsAttention deficits– Fine motor deficitsFine motor deficits– Language deficitsLanguage deficits– Visual-spatial dysfunctionVisual-spatial dysfunction– Verbal memory deficitsVerbal memory deficits

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Legislative AuthorityLegislative Authority

Health and Safety Code, Section Health and Safety Code, Section

436.003 et seq. The 436.003 et seq. The

commissioner by order shall commissioner by order shall

declare any public water to be a declare any public water to be a

prohibited area if. . . area prohibited area if. . . area

contains aquatic life that is unfit contains aquatic life that is unfit

for human consumptionfor human consumption

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Risk Assessment ComponentsRisk Assessment Components

Problem IdentificationProblem Identification Toxicity AssessmentToxicity Assessment Receptor CharacterizationReceptor Characterization Exposure AssessmentExposure Assessment Risk CharacterizationRisk Characterization Risk ManagementRisk Management

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IDENTIFY PROBLEMIDENTIFY PROBLEM(Methylmercury)(Methylmercury)

1.1. Select water body and target species: Select water body and target species: Likely present in high-trophic level, Likely present in high-trophic level, older, leaner fisholder, leaner fish

2.2. Obtain samples of target speciesObtain samples of target species

3.3. Analyze tissue from target species for Analyze tissue from target species for total mercurytotal mercury

4.4. Determine concentration of mercury: Determine concentration of mercury: total mercury concentration assumed total mercury concentration assumed to equal methylmercury in tissue to equal methylmercury in tissue (mg/kg) (mg/kg)

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CHARACTERIZE CHARACTERIZE RECEPTOR(s)RECEPTOR(s)

•Population at Risk: Humans Population at Risk: Humans Sensitive Sub-groupsSensitive Sub-groups

•FETUS-via pregnant women, women FETUS-via pregnant women, women who may become pregnantwho may become pregnant

•Cross-placentalCross-placental

•INFANT?-via nursing mothers or direct INFANT?-via nursing mothers or direct consumption at early ageconsumption at early age

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CHARACTERIZE RECEPTOR CHARACTERIZE RECEPTOR (humans)(humans)

• ADOLESCENT and ADULT MALES, ADOLESCENT and ADULT MALES, WOMEN WHO CANNOT BEAR WOMEN WHO CANNOT BEAR CHILDRENCHILDREN

Low level exposure-likely no visible or Low level exposure-likely no visible or long-term effects long-term effects

High level exposure-likely visible, acute High level exposure-likely visible, acute toxicity toxicity

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ASSESS TOXICITY of ASSESS TOXICITY of METHYLMERCURY METHYLMERCURY

• Health-based Comparison Values Health-based Comparison Values (HACs)(HACs)

• Systemic toxicitySystemic toxicity– RfD x BW RfD x BW ÷ Consumption RateConsumption Rate– 0.0003 X 70 0.0003 X 70 ÷0.030 = 0.7 mg/kg tissue÷0.030 = 0.7 mg/kg tissue

• Cancer – not an issue with MeHgCancer – not an issue with MeHg

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Assumptions for Establishing Assumptions for Establishing GuidelinesGuidelines

Adult Body weight (BW): 70 kgAdult Body weight (BW): 70 kg

Consumption rate (CR) 0.03 kg/day (8 oz/wk)Consumption rate (CR) 0.03 kg/day (8 oz/wk)

––and, for Cancerand, for Cancer

Acceptable Risk Level (ARL): 1 extra Acceptable Risk Level (ARL): 1 extra cancer/10,000 exposed personscancer/10,000 exposed persons

Exposure period: 30 yearsExposure period: 30 years

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PRODUCE RISK PRODUCE RISK CHARACTERIZATION REPORTCHARACTERIZATION REPORT

• Introduction and Statement of the Introduction and Statement of the ProblemProblem

• Materials and MethodsMaterials and Methods• ResultsResults• DiscussionDiscussion

– ConclusionsConclusions– Recommendations for reducing exposure-Recommendations for reducing exposure-– Communication of Health Risk to PublicCommunication of Health Risk to Public

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RISK MANAGEMENTRISK MANAGEMENT

•Decision-making process used toDecision-making process used to::

– Develop, analyze, and compare regulatory Develop, analyze, and compare regulatory options options

– Select appropriate regulatory responses to Select appropriate regulatory responses to a potential or current public health hazarda potential or current public health hazard

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Communicating Risk from Communicating Risk from Consumption of Contaminated Fish Consumption of Contaminated Fish

Press releasesPress releases Publications: Publications: Seafood and Aquatic Life Group Web SiteSeafood and Aquatic Life Group Web Site

http:/ /http:/ / www.dshs.state.tx.us/seafood/fishwww.dshs.state.tx.us/seafood/fishConsump.stmConsump.stm–– Fish Consumption Advisories and BansFish Consumption Advisories and Bans–– Outdoor Annual Hunting and Fishing Outdoor Annual Hunting and Fishing

RegulationsRegulations (Texas Parks and Wildlife (Texas Parks and Wildlife DepartmentDepartment-- lists bans only)lists bans only)

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Questions?Questions?