National Descriptive Model of Mercury in Fish TissueStephen P. WenteMounds View, MNU.S. Department of the Interior U.S. Geological Survey

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Sampling for Mercury in Fish Spatial variationTemporal variationFish consumption advisories

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Problem 1: Cost of Information

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Possible Sample DesignsCollect fish samples with consistent characteristicsSpecies confined to definite rangesCannot compare to existing dataUse existing dataMust use model to make samples comparableVariations in quality of existing studies

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Problem 2: Difficult Comparisons

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Fish Mercury (Hg) Model DetailsRegression method (Covariance model)Accounts for:Less than detection limit valuesSpecies (Hg increases with trophic position)Tissues sampled (skin-off fillet > skin-on > whole fish)Fish length (larger fish are higher in Hg)Calibrated to national dataset (N=45,605)

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Simple yet Realistic DescriptionLog-log SpaceArithmetic Space

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Consumption Advisory

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Standardize Sample Type

Sampling EventsSpecies1234567AXXXBXXXXXCXXXXDXXXX

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Modeled Spatial Variation(14 inch Largemouth Bass Skin-off Fillets)

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Northwestern US Fish Hg Trends:NCBP Data19651990(NCBP = National Contaminant Biomonitoring Program)

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Analytical Cost Reduction*Sample types is number of species size classes tissue types

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Model Reduces Compliance Costs by Reducing Uncertainty

Project Website (emmma.usgs.gov)

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Benefits of National ModelConsistent nationwide interpretation of many independent monitoring effortsMore comprehensive fish consumption advisoriesBetter description of spatial and temporal trendsReduced analytical and compliance costsContact: Steve Wente (spwente@usgs.gov)

2004 Mercury Workshop in Reston2004 Mercury Workshop in RestonSlopes become exponents describing curvatureIntercepts become multiplication factorsError has a log-normal distribution