Grantee Research Project Results
2012 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, 2012 through March 31,2013
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 the critical link between Hg exposure and the amount of selenium (Se) present in the fish. Because Se-dependent enzymes are required for normal brain physiology and development, the irreversible inhibition of their activities by MeHg is the primary mechanism of MeHg toxicity. Also, because MeHg exposures become increasingly hazardous as MeHg:Se molar ratios in tissues approach and exceed equimolar stoichiometries, but similar or higher MeHg exposures are without effect among Se-replete subjects, this appears to be the exclusive mechanism of MeHg toxicity. Thus, it is not surprising that human studies that have found adverse effects from Hg exposures uniformly involved populations that were exposed to Hg by consuming pilot whale meats (Faroe Islands) or other, similarly high Hg, low Se seafoods such as shark (New Zealand). Meanwhile, child and maternal health has been found to be greatly benefited by maternal consumption of fish that are rich in Se relative to Hg (e.g., Seychelles, United Kingdom). Because MeHg was not in molar excess, the combined salutary effects of improved omega-3, vitamin D, vitamin E, iodine, and Se nutritional status from ocean fish need to be considered.
As consumers would find it challenging to evaluate the molar relationships between Hg and Se for themselves, a seafood safety criterion known as the Selenium Health Benefit Value (HBVSe) was developed. During the course of the past year, an improved equation was developed, and this criterion was evaluated in ~10,000 ocean and fresh water fish. These criteria provide more reliably consistent assessments of health effects associated with seafood consumption: HBVSe = (Se – Hg)/Se • (Se + Hg)
Maternal consumption of seafoods with positive values that indicate they contain Se is present in molar excess of Hg would be expected to be associated with beneficial outcomes, and this coincides with the findings of human and animal studies of this issue. Meanwhile, those with negative values (which only occurs in meats of predatory whales and certain varieties of shark, swordfish, but relatively few other seafoods) indicate those that would be expected to be associated with adverse effects, and this once again corresponds with the findings of human and animal studies. Among freshwater fish, the issue is far more urgent to examine since environmental Se can vary dramatically and MeHg is known to accumulate at much higher levels in fish from water bodies that have poor Se resources. The objective of this study is to establish HBVSe of ocean and freshwater fish in an effort to identify those that may pose consumption risks and therefore should be avoided by young children and women that are or may become pregnant, especially in subpopulations that may be at accentuated risk due to malnourishment.
To improve the reliability and accuracy of Hg risk assessments, Physiologically Oriented Interactions of Nutrients and Toxicants (POINT) model evaluations consider the effects of nutritional status in relation to MeHg exposures.
Progress Summary:
Data on ~10,000 ocean and freshwater fish have been acquired and their HBVSe has been evaluated. With few exceptions, ocean fish and other seafoods were found to have positive HBVSe. Although the HBVSe of these varieties of fish decline as the fish grow larger and older (and Hg bioaccumulates), in almost all cases their HBVSe remains positive in even the largest specimens. The only exceptions were meats of predatory whales, certain varieties of shark, swordfish, and halibut. Although king mackerel and tilefish were not available for assessment, it is clear that the current FDA/EPA advisory regarding seafood varieties that should be avoided during pregnancy is substantiated and confirmed by this study.
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 fish consumption risks (fish with negative HBVSe) appear to warrant increased monitoring. As we had hypothesized, freshwater fish species with MeHg bioaccumulations in molar excess of Se 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. The effect of environmental Se on Hg bioaccumulation was highly significant in most varieties of freshwater fish and is likely to have similarly important effects on Hg bioaccumulation in fish from estuaries. Therefore, based on the environmental availability of Se, it may be possible to predict where fish with negative HBVSe will occur. Because the environmental variability of Se can be dramatic, there is an urgent need for more extensive and intensive examinations of the relative amounts of Hg and Se in freshwater fish in water bodies across North America.
The results of our POINT model continue to improve our understanding of how and why the responses to maternal Hg exposures in major epidemiological studies of seafood consumption have appeared to contrast with one another. It is now clear that rather than being in conflict, the findings of these studies exactly coincide with theoretical expectations based on the HBVSe of the seafoods that were consumed in the various studies.
Future Activities:
In the coming year, we are focusing on completion of the compilation of our evaluations of ocean and freshwater fish and the POINT models of Hg–Se interactions. Articles describing work from this project are currently being written for environmental and health-related journals.
Data on ~1,000 more fish samples are being added to the ocean and freshwater fish databases, bringing the total up to ~11,000 samples. Work on the animal and human POINT models is continuing.
Articles describing our research findings are in preparation for submission to journals.
The Council Liaison Group of the Society of Toxicology is nominating Dr. Ralston to the U.S. Food and Drug Administration’s Food Advisory Committee.
Dr. Raymond has been invited to present a Grand Rounds lecture at Altru Hospital that is tentatively entitled “Benefits of Ocean Fish Consumption” on August 7, 2013, Grand Forks, ND.
Dr. Ralston has been invited to present a lecture on global health implications of mercury-selenium interactions at the 3rd International Selenium Conference in HeFei, China, November 10-14, 2013.
Dr. Ralston has been asked to present his lecture, “Seafood Consumption During Pregnancy; The Good News: Seafood is Safe & Beneficial. The Bad News: Not Enough People Know It,” at the ATID (Israeli Dietitian’s Association) in Tel Aviv, Israel, October 9–10, 2013.
Dr. Ralston proposed a symposium session for the International Society of Toxicology 2014 Meeting: “Methylmercury's Modes of Action: New Approaches to Understanding an Old Problem.” Dr. Ralston will chair the symposium which will involve the leading experts in mercury toxicology from around the world. Dr. Ralston’s presentation will be; “The Five ‘SOS’ Molecular Mechanisms of Mercury Toxicity.”
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, endocrineRelevant Websites:
Energy & Environmental Research Center ExitProgress 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.