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Mercury Study Report to Congress United States EPA-452/R-97-005 Environmental Protection December 1997 Agency Air Mercury Study Report to Congress Volume III: Fate and Transport of Mercury in the Environment Office of Air Quality Planning & Standards and Office of Research and Development c7o032-1-1 MERCURY STUDY REPORT TO CONGRESS VOLUME III: FATE AND TRANSPORT OF MERCURY IN THE ENVIRONMENT December 1997 Office of Air Quality Planning and Standards and Office of Research and Development U.S. Environmental Protection Agency TABLE OF CONTENTS Page U.S. EPA AUTHORS ................................................................ v SCIENTIFIC PEER REVIEWERS ......................................................vi WORK GROUP AND U.S. EPA/ORD REVIEWERS .......................................ix LIST OF TABLES ................................................................... x LIST OF FIGURES .................................................................xiii LIST OF SYMBOLS, UNITS AND ACRONYMS ........................................xiv EXECUTIVE SUMMARY ......................................................... ES-1 1. INTRODUCTION ...........................................................1-1 1.1 Long Range Atmospheric Transport Modeling ...............................1-4 1.2 Local Atmospheric Transport Modeling ....................................1-4 1.3 Modeling Terrestrial and Aquatic Fate of Mercury ...........................1-5 1.4 Exposure Modeling Rationale ............................................1-6 1.5 Factors Important in Modeling of Mercury Exposure ..........................1-7 1.6 Definition of Terms....................................................1-9 2. OVERVIEW OF MERCURY FATE AND TRANSPORT ............................2-1 2.1 Mercury in the Environment .............................................2-1 2.1.1 Chemistry of Mercury ............................................2-2 2.1.2 The Mercury Cycle ..............................................2-2 2.1.2.1 The Global Mercury Cycle .................................2-3 2.1.2.2 Regional and Local Mercury Cycles ..........................2-4 2.2 Atmospheric Processes .................................................2-6 2.2.1 Emissions of Mercury ............................................2-6 2.2.2 Mercury Transformation and Transport ..............................2-7 2.2.3 Deposition of Mercury ...........................................2-9 2.2.4 Re-emissions of Mercury into the Atmosphere .......................2-11 2.3 Terrestrial and Aquatic Fate of Mercury ...................................2-11 2.3.1 Mercury in Soil ................................................2-11 2.3.2 Plant and Animal Uptake of Mercury ...............................2-12 2.3.3 Mercury in the Freshwater Ecosystem ..............................2-12 2.4 Fate of Mercury in Marine Environments ..................................2-14 2.4.1 Models of Mercury in the Oceans .................................2-15 2.4.2 Modeling Estuaries and Coastal Regions ............................2-16 2.4.3 Mercury Budget for a Coastal Waterbody in U.S.A. ...................2-18 3. MEASURED CONCENTRATIONS .............................................3-1 3.1 Analytic Measurement Methods ..........................................3-1 3.2 Measurement Data .....................................................3-1 3.2.1 Mercury Air Concentrations .......................................3-1 3.2.2 Mercury Concentrations in Precipitation .............................3-4 3.2.3 Mercury Deposition Rates ........................................3-5 3.2.4 Mercury Concentrations in Water ..................................3-8 i TABLE OF CONTENTS (continued) Page 3.2.5 Mercury Concentrations in Soil/Sediment ...........................3-10 3.2.6 Mercury Concentrations in Biota ..................................3-13 3.3 Measurement Data from Remote Locations ................................3-30 3.3.1 Elevated Atmospheric Mercury Concentrations over Remote Locations . 3-30 3.3.2 Elevated Soil Mercury Concentrations in Locations Remote from Emission Sources ......................................................3-30 3.3.3 Elevated Mercury Concentrations in Aquatic Sediments and Fish from Remote Water Bodies .................................................3-31 3.4 Measurement Data Near Anthropogenic Sources of Concern ...................3-31 3.4.1 Municipal Waste Combustors .....................................3-32 3.4.2 Chlor-Alkali Plants .............................................3-33 3.4.3 Coal-Fired Utilities .............................................3-33 3.4.4 Mercury Mines ................................................3-34 3.4.5 Mercury Near Multiple Local Sources ..............................3-34 4. MODEL FRAMEWORK ......................................................4-1 4.1 Models Used .........................................................4-1 4.2 Modeling of Long-Range Fate and Transport of Mercury ......................4-1 4.2.1 Objectives .....................................................4-1 4.2.2 Estimating Impacts from Regional Anthropogenic Sources of Mercury .....4-2 4.2.3 Description of the RELMAP Mercury Model .........................4-2 4.2.3.1 Physical Model Structure ...................................4-3 4.2.3.2 Mercury Emissions .......................................4-3 4.2.3.3 Carbon Aerosol Emissions .................................4-9 4.2.3.4 Ozone Concentration ......................................4-9 4.2.3.5 Lagrangian Transport and Deposition ........................4-10 4.2.4 Model Parameterizations ........................................4-10 4.2.4.1 Chemical Transformation and Wet Deposition .................4-10 4.2.4.2 Dry Deposition ..........................................4-12 4.2.4.3 Vertical Exchange of Mass with the Free Atmosphere ...........4-15 4.3 Modeling the Local Atmospheric Transport of Mercury in Source Emissions ......4-16 4.3.1 Phase and Oxidation State of Emitted Mercury .......................4-16 4.3.2 Modeling the Deposition of Mercury ...............................4-17 4.3.3 Rationale and Utility of Model Plant Approach .......................4-21 4.3.4 Development and Description of Model Plants .......................4-21 4.3.5 Hypothetical Locations of Model Plants ............................4-22 4.4 Modeling Mercury in a Watershed .......................................4-24 4.4.1 Overview of the Watershed Model .................................4-24 4.4.2 Description of the Watershed Soil Module ..........................4-26 4.4.2.1 Development of Soil Mass Balance Equations .................4-28 4.4.2.2 Loads to Watershed Soils .................................4-30 4.4.2.3 Equilibrium Speciation Reactions ...........................4-31 4.4.2.4 Transformation Processes in Watershed Soils .................4-32 4.4.2.5 Transport and Transfer Processes in Watershed Soils ...........4-32 4.4.3 Description of the Water Body Module .............................4-34 ii TABLE OF CONTENTS (continued) Page 4.4.3.1 The Water Body Equations ................................4-35 4.4.3.2 The Solids Balance Equations ..............................4-39 4.4.3.3 Loads to the Water Body ..................................4-40 4.4.3.4 Equilibrium Speciation Reactions ...........................4-42 4.4.3.5 Transformation Processes in the Water Body ..................4-43 4.4.3.6 Transport and Transfer Processes in the Water Body ............4-44 5. ATMOSPHERIC FATE AND TRANSPORT MODELING RESULTS .................5-1 5.1 Long Range Atmospheric Fate/Transport Modeling ...........................5-1 5.1.1 Mass Balances of Mercury within the Long-range Model Domain .........5-1 5.1.2 Qualitative Description of Mercury Concentration Results ...............5-2 5.1.3 Description of Mercury Wet Deposition Simulation Results ..............5-8 5.1.4 Qualitative Description of Mercury Dry Deposition Results .............5-19 5.1.5 Qualitative Description of Total Mercury Deposition Results ............5-24 5.1.6 General Data Interpretations of the RELMAP Modeling ................5-26 5.2 Overview of Local Scale Analysis: Background Concentrations ...............5-27 5.2.1 Introduction ...................................................5-27 5.2.2 The Pre-anthropogenic Mercury Cycle ...........................5-28 5.2.3 Estimating Current Background Mercury Concentrations ...............5-30 5.3 Local Atmospheric Transport Modeling ...................................5-36 5.3.1 Air Concentrations .............................................5-40 5.3.2 Deposition Rates ...............................................5-40 5.3.3 Mass Balances within the Local-Scale Domain .......................5-41 5.3.4 Uncertainty and Sensitivity Analyses ...............................5-47 5.3.4.1 Dry Deposition ..........................................5-47 5.3.4.2 Wet Deposition .........................................5-53 5.3.4.3 Sensitivity to Emissions Speciation ..........................5-53 5.3.4.4 Effect of Terrain on Results of Local Scale Modeling ...........5-54 6. WATERSHED FATE AND TRANSPORT MODELING ............................6-1 6.1 Overview ............................................................6-1 6.2 Watershed and Waterbody Results for Pre-anthropogenic Mercury Cycle and the Current Mercury Cycle .................................................6-1 6.3 Watershed/Waterbody Model Results for Local Scale Analysis ..................6-2 6.4 Variability and Sensitivity Analysis .......................................6-8
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