Grantee Research Project Results
2011 Progress Report: Fish Selenium Health Benefit Values in Mercury Risk Management
EPA Grant Number: R834792Title: Fish Selenium Health Benefit Values in Mercury Risk Management
Investigators: Ralston, Nicholas V.C. , Raymond, Laura
Institution: University of North Dakota
EPA Project Officer: Hahn, Intaek
Project Period: April 1, 2011 through March 31, 2013 (Extended to March 31, 2015)
Project Period Covered by this Report: April 1, 2011 through March 31,2012
Project Amount: $490,089
RFA: Exploring Linkages Between Health Outcomes and Environmental Hazards, Exposures, and Interventions for Public Health Tracking and Risk Management (2009) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Human Health
Objective:
This project extends development of a reliably accurate indicator of methylmercury (MeHg)-associated risks in order to provide a critical link between Hg exposure and the effects of fish consumption. Fish consumption warnings, based on the amount of MeHg present in the fish, fail to consider the beneficial nutrients that are also present. Based on the current understanding of the molecular mechanism of MeHg toxicity (inhibition of synthesis and activity of selenium (Se)-dependent enzymes that are required for brain and endocrine health), it is clear that in order to be reliably accurate, the molar ratios of Se and MeHg both need to be considered in Hg risk assessments. Using this approach, our prior U.S. Environmental Protection Agency (EPA)-funded research has resulted in development of the Se-Health Benefit Value (Se-HBV) as an indicator of fish consumption safety. The Se-HBV is calculated using the following formula:
Se-HBV = (Se:Hg molar ratio x Se concentration) − (Hg:Se molar ratio x Hg concentration).
Because they contain Hg in molar excess of Se, fish with negative Se-HBVs may not be safe to eat. Predictions of the effects of maternal fish consumption on child health outcomes based on MeHg exposures alone have not been consistent with the findings of human studies, but predictions of child outcomes based on Se-HBV criteria have proved to be reliable. This study is evaluating the Se-HBVs of commonly consumed varieties of ocean and freshwater fish and assessing the biochemical basis of adverse effects that have been observed in association with high Hg exposures.
Progress Summary:
Requests for data were sent out to all federal, state, and industrial organizations known to analyze Hg or Hg and Se concentrations in ocean and freshwater fish. Data from most organizations were readily shared, and data on several thousand individual fish samples were acquired. The available data were compiled, and the Se-HBVs of these ocean fish and freshwater fish species were calculated and are being assessed. With few exceptions, the majority of varieties of ocean fish and other seafoods were found to have positive Se-HBVs. Although the Se-HBVs of these varieties of fish were all found to decline as the fish grow larger and older (primarily because of Hg bioaccumulation), in most cases the Hg:Se molar ratios in these species do not appear likely to become negative in even the largest specimens. Varieties of ocean fish with low or negative Se-HBVs tended to be top predatory species, primarily certain varieties of shark.
The concentrations of Hg and Se present in freshwater fish were far more variable than those observed in ocean fish. The relationships between fish Hg and Se contents were investigated in relation to weight to identify varieties and locations where accentuated risks due to Hg content in excess of Se occur. As we had hypothesized, freshwater fish species with MeHg bioaccumulations in molar excess of Se tend to arise in regions of North America with notably Se poor soils or areas with low pH that limit the biological availability of Se naturally present in soil and water. Therefore, the regions where accentuated risks associated with high Hg exposures associated with consumption of freshwater fish with negative Se-HBVs may be possible to predict are based on the environmental availability of Se.
This project is currently developing a computational Physiologically Oriented Interactions of Nutrients and Toxins (POINT) model to refine understanding of the biological responses associated with Hg-dependent inhibition of Se enzymes and sequestration of Se in the form of HgSe in tissues. Consideration of these and related interactions at the molecular, cellular, and organ tissue levels observed in laboratory animal and human epidemiological studies is being used in order to improve the accuracy of Se-HBV criteria.
Future Activities:
In the second year, we are focusing on completion of the compilation of Hg and Se data in ocean and freshwater fish and the POINT models of HgSe interactions. Articles describing work from this project are being written for environmental and health-related journals.
We are also contacting organizations that assess Hg concentrations in ocean or freshwater fish. Those that are currently only assessing Hg concentrations in fish samples will continue to be encouraged to also assess Se. They will also be encouraged to assess elemental concentrations in individual fish instead of composite samples and to record fish size and weights of the fish being analyzed.
In areas where freshwater fish are expected to pose Hg-related risks to humans and wildlife, we are recommending analysis of Hg and Se in fillets (for human risk assessments) in coordination with Hg and Se concentrations in homogenates of the whole fish (for wildlife risk assessments). Since the risks of Hg exposures from fish consumption depend on the Se:Hg molar ratios of the fish, elemental analysis results should transition to being reported on a molar (µmol/kg) instead of a mass (µg/kg) basis.
Journal Articles:
No journal articles submitted with this report: View all 25 publications for this projectSupplemental Keywords:
ocean fish, freshwater fish, fish consumption, mercury, mercury exposure, toxicity, selenium, selenoenzyme, brain, endocrine
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.