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Mercury concentrations in fillets of fish collected in the U.S. EPA National Rivers and Streams Assessment of the continental USA
Citation:
O'Bryan, E., J. Webb-Turbeville, M. CRANE, A. BATT, J. M. LAZORCHAK, L. STAHL, L. STAHL, AND J. Wathen. Mercury concentrations in fillets of fish collected in the U.S. EPA National Rivers and Streams Assessment of the continental USA. 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 National Rivers and Streams Assessment (NRSA) is a statistical survey of flowing waters of the U.S. The purpose of this survey was to assess the condition of the nation's rivers and streams, establish a baseline to evaluate progress of pollution control activities in flowing waters of the U.S., and generate statistically valid and environmentally relevant reports on the condition of the nation's water resources. The survey measured a wide variety of variables intended to characterize chemical, physical and biological condition. These variables included nutrients, chlorophyll-a, other water chemistry analytes, sediment enzymes, enterococci, fish tissue, physical habitat and biological characteristics, including assessments of phytoplankton, periphyton, benthic macroinvertebrates and fish communities. In 2008 and 2009, fish were collected from about 650 streams and rivers, including a representative subset of 183 urban river sites. The U.S. EPA analyzed fish fillets for 22 pesticides, 20 congeners of PCBs, 8 congeners of PBDEs, mercury, selenium, % lipids and % moisture. Mercury was detected in all samples and ranged from 14.8 to 1418.54 ng/g in the fish fillet samples, an unaverage concentration across all samples of 230.91 ng/g and a median of 174.95 ng/g. Nearly 26% of the samples exceeded the EPA 300 ng/g screening value for recreational fishing and about 98% of the samples exceeded a wildlife screening value of 30 ng/g. A statistical analyses and assessment from a national scale will be presented.