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Comparison of mercury and selenium concentrations in whole fish and fillets analyzed in fish collected in the Lower Mississippi River
Citation:
CRANE, M., E. O'Bryan, J. Webb-Turbeville, A. BATT, J. M. LAZORCHAK, T. R. ANGRADI, D. W. BOLGRIEN, AND L. STAHL. Comparison of mercury and selenium concentrations in whole fish and fillets analyzed in fish collected in the Lower Mississippi River. Presented at SETAC, Boston, MA, November 13 - 17, 2011.
Impact/Purpose:
A great deal of uncertainty exists regarding the extent to which humans and wildlife are exposed to chemical stressors in aquatic resources. Scientific literature is replete with studies of xenobiotics in surface waters, including a recent national USGS survey of endocrine disrupting chemicals; however, biological significance of these chemical data is in question since chemical bioavailability is largely unknown and biological events may be induced by undetected chemicals and varying ecological conditions (i.e., total nitrogen and phosphorus). Whole effluent toxicity data exist, but do not answer specific exposure questions that may support detailed ecological risk assessments. Interpretation of data arising from exposure to complex chemical mixtures is even more problematic. A solution to these problems is development of sensitive and specific cellular indicators of exposure in aquatic organisms. The potential for development is enhanced by emergent resources in molecular biology and associated technologies, most notably DNA microarrays consisting of transcriptionally relevant nucleic acid sequences that can be used to detect altered gene expression in cells, tissues and various life stages of organisms exposed to chemical and natural stressors. Ecological investigation in the present Task have been partitioned into three focal research areas: (1) Core Computational Toxicology research, (2) Ecological research and (3) Molecular Diagnostics and endocrine disrupting compounds. Three areas of core and applied research will be consequential on development of molecular indicators diagnostic for exposure to specific xenobiotic, natural stressors, and complex mixtures thereof, in freshwater fish and invertebrates. Research is focused on Agency’s long-established aquatic toxicological organism, the fathead minnow (Pimephales promelas). Although numerous molecular biological approaches are exploited, foremost methods leading to development of molecular indicators are assembly and manufacture of DNA microarrays containing transcriptionally relevant gene sequences of fathead minnow, and the detection of novel or differentially expressed proteins by means of 2-D polyacrylamide gel electrophoresis followed by mass spectrometry. An extensive effort in 'gene discovery' research with the fathead minnow has been the primary emphasis of respective research areas, since high-throughput genome sequencing efforts-such as those in human and mouse-have not been directed toward organisms used in aquatic toxicity testing such as fathead minnows. Gene discovery research is fundamental to identified research areas, and is expected to be augmented by high-throughput cDNA sequencing data arising through a collaborative effort with the Dept. of Energy, Joint Genome Institute. Also, proteins induced to differential expression by chemical exposure will be used in ‘reverse genetics’ approach wherein knowledge of protein sequence will make possible the investigation of gene function and associated mechanistic biology. Following development and validation, fathead minnow microarrays, along with critical indicators identified by expression proteomics, will enable extensive molecular profiling studies, the hypotheses of which are that unique patterns of gene expression will be detected in targeted tissues of fathead minnows exposed to individual chemical stressors. Identification of unique, differentially expressed genes will then provide the basis for stressor-specific, quantitative molecular indicators, theory and methods that can be readily transferred to investigators within USEPA Regions, Tribes and states.
Description:
The science and practice of environmental assessment have been advanced by research done by the U.S. EPA Office of Research and Development's (ORD) Environmental Monitoring and Assessment Program (EMAP). In short, the condition of a resource can be estimated from key chemical, physical and biological measurements at relatively few sites. It is analogous to a public opinion survey where the responses of a few people provide estimates for the entire population. EMAP's statistical sampling designs and biological indicators are well developed. The Office of Water (OW) has adopted them for its national assessments of aquatic resources. As part of the U.S. EPA National Rivers and Streams Assessment (NRSA) and EMAP Great Rivers (GRE) Projects, 13 urban sites and 43 non-urban sites on the lower Mississippi River were sampled for fish to be analyzed for mercury and selenium in whole fish and fillets. In a previous EMAP GRE study, the upper Mississippi River was sampled but only whole fish samples were analyzed for Hg. EMAP-GRE focused on whole fish because of its emphasis on the health of the ecosystem. Although whole fish contamination is primarily an indicator of risk to piscivorous wildlife, whole fish data are still relevant for estimating human risk from fish consumpton. At each of the 56 sites, three fish samples were collected: a primary, a secondary sample and a sample for fillets. A comparison was made between whole fish secondary samples and fillets. Preliminary analyses indicate that whole fish levels of Hg were found to be from 19% less to 30% higher than fillets and selenium was found to be 13% less and 42% higher than fillets. A statistical analyses and assessment of whole fish and fillets concentrations vs. wildlife and human risk of consumption will be presented.