The Role of Fishes as Transporters of Mercury

EPA Grant Number: R825433C012
Subproject: this is subproject number 012 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: The Role of Fishes as Transporters of Mercury
Investigators: Cech, Joseph
Institution: University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


This project seeks to determine the dietary methylmercury uptake rates and physiological effects on the Clear Lake native Sacramento blackfish.


It is now known that several species of fish in Clear Lake, CA contain high levels of methylmercury in their flesh. Mercury leaches into the lake from naturally occurring cinnabar ores in the basin drainage and from anthropogenic sources such as the Sulphur Bank Mercury Mine. These sources yield both organic and inorganic mercury, and natural biological processes can convert them to methylmercury, which is readily taken up by aquatic organisms and biomagnifies up the food chain. Fish are abundant in the naturally eutrophic Clear Lake, and levels in edible fish tissue from Clear Lake have exceeded the maximum limits set by the U.S. Food and Drug Administration. The Sacramento blackfish, a native planktivore, is an important component of the Clear Lake ecosystem and it is commercially fished for human consumption. While it well documented that mercury accumulates in tissue following exposure, relatively little is known about the mechanisms involved in uptake and the physiological effects that mercury exerts on fish.

The investigators conducted a food consumption, growth, routine metabolism (oxygen consumption rate), optomotor response, and swimming performance (critical swimming velocity) study on young-of-the-year Sacramento blackfish. Fish were exposed to sub-lethal concentrations of methylmercury (MeHg) in their diet (control, low, medium, and high doses) for the duration of the study. We used 35 fish per tank and there were 6 tanks per treatment group. Each fish was tested individually. Throughout the experiment, fish were weighed, measured, and subsamples were taken to determine tissue concentrations of mercury. Analysis of these tissues, by cold vapor AA, has just been completed, and these will be compared with each fish's performance in the various challenge tests. Results from individual experiments were analyzed statistically (single-factor ANOVA models at the 95% confidence level).

They found that although all four treatment groups' food consumption rates were statistically indistinguishable, growth rates differed between the treatment groups. The high dose fish (fed a diet containing 50 mg/kg methylmercury) grew slower than both the low dose (fed a diet of 0.45 mg/kg methylmercury) and the control group (no added methylmercury). There were no differences among the treatment groups' wet weight/dry weight ratios or among their resting metabolic rates. However, the high dose group was unable to perform as well as the other groups in the swimming performance challenge. This was a significant result in a trend of diminished swimming performance with increasing mercury levels in the diet across all treatment groups.

The investigators also attempted an immune challenge with Vibrio to assess the effects of methylmercury on a blackfish's ability to withstand a bacterial challenge. Interestingly, the blackfish's high Vibrio resistance precluded the successful completion of the challenge.

Expected Results:

The expected results are to finish the analyses of the dietary MeHg-exposed blackfish, score the videotaped optomotor challenge, and prepare a manuscript for publication. The investigators will also continue to collaborate with other CEHR investigators in developing Clear Lake mercury uptake/transport/fate models. Their data on food consumption rate, mercury accumulation rate, growth rate, metabolic rate, swimming performance will help to assess the risks of physiological compromise (e.g., in terms of decreased growth, swimming performance) in fishes that are chronically exposed to sub-lethal concentrations of dietary methylmercury and the consequent roles of fish in the mercury uptake/transport/fate models.

Supplemental Keywords:

watershed, aquatic ecosystem restoration, Clear Lake, mercury, fate and transport, ecosytem modeling, Sacramento blackfish, methylmercury., RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Water, INDUSTRY, Ecosystem Protection/Environmental Exposure & Risk, HUMAN HEALTH, Aquatic Ecosystems & Estuarine Research, mercury transport, Health Risk Assessment, Exposure, Aquatic Ecosystem, Risk Assessments, Biochemistry, Physical Processes, Ecological Risk Assessment, Industrial Processes, Biology, Mercury, mercury uptake, human consumption, contaminant exposure, marine food web, chemical exposure, fate and transport, Sacramento blackfish, Clear Lake , food chain, food web, marine biology, bioavailability, fish communities, Clear Lake, fish consumption, methylmercury, human exposure, mining, watershed influences, aquatic ecosystems, mercury contamination in fish, mercury methylation, dietary exposure, bioaccumulation, fish-borne toxicants, human health risk, lake ecosystems

Progress and Final Reports:

  • 1997
  • 1998
  • 1999
  • Final Report

  • Main Center Abstract and Reports:

    R825433    EERC - Center for Ecological Health Research (Cal Davis)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
    R825433C002 Sacramento River Watershed
    R825433C003 Endocrine Disruption in Fish and Birds
    R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
    R825433C005 Fish Developmental Toxicity/Recruitment
    R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
    R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
    R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
    R825433C009 Modeling Ecosystems Under Combined Stress
    R825433C010 Mercury Uptake by Fish
    R825433C011 Clear Lake Watershed
    R825433C012 The Role of Fishes as Transporters of Mercury
    R825433C013 Wetlands Restoration
    R825433C014 Wildlife Bioaccumulation and Effects
    R825433C015 Microbiology of Mercury Methylation in Sediments
    R825433C016 Hg and Fe Biogeochemistry
    R825433C017 Water Motions and Material Transport
    R825433C018 Economic Impacts of Multiple Stresses
    R825433C019 The History of Anthropogenic Effects
    R825433C020 Wetland Restoration
    R825433C021 Sierra Nevada Watershed Project
    R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
    R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
    R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
    R825433C025 Regional Movement of Toxics
    R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
    R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
    R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
    R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
    R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
    R825433C031 Pre-contact Forest Structure
    R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
    R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
    R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
    R825433C035 Border Rivers Watershed
    R825433C036 Toxicity Studies
    R825433C037 Watershed Assessment
    R825433C038 Microbiological Processes in Sediments
    R825433C039 Analytical and Biomarkers Core
    R825433C040 Organic Analysis
    R825433C041 Inorganic Analysis
    R825433C042 Immunoassay and Serum Markers
    R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
    R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
    R825433C045 Microbial Community Assays
    R825433C046 Cumulative and Integrative Biochemical Indicators
    R825433C047 Mercury and Iron Biogeochemistry
    R825433C048 Transport and Fate Core
    R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
    R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
    R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
    R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
    R825433C053 Currents in Clear Lake
    R825433C054 Data Integration and Decision Support Core
    R825433C055 Spatial Patterns and Biodiversity
    R825433C056 Modeling Transport in Aquatic Systems
    R825433C057 Spatial and Temporal Trends in Water Quality
    R825433C058 Time Series Analysis and Modeling Ecological Risk
    R825433C059 WWW/Outreach
    R825433C060 Economic Effects of Multiple Stresses
    R825433C061 Effects of Nutrients on Algal Growth
    R825433C062 Nutrient Loading
    R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
    R825433C064 Chlorinated Hydrocarbons
    R825433C065 Sierra Ozone Studies
    R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
    R825433C067 Terrestrial - Agriculture
    R825433C069 Molecular Epidemiology Core
    R825433C070 Serum Markers of Environmental Stress
    R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
    R825433C072 Molecular Monitoring of Microbial Populations
    R825433C073 Aquatic - Rivers and Estuaries
    R825433C074 Border Rivers - Toxicity Studies