Trophic interaction vs. direct uptake
Williams, Barry James
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Coal is still used as a major source of fuel for power plants in the U. S. and worldwide. One of the many forms of the combusted waste is fly ash, a fine particulate matter that is sometimes mixed with water and pumped to settling basins. This form of waste removal is currently used at the D-Area power plant on the Savannah River Site near Aiken, SC. Many of the metal and metalloid constituents of the coal residue are known to have chronic toxic effects on biota. Definite pathways into aquatic organisms are poorly understood. The research examined the distribution of coal-associated contaminants among aquatic flora and fauna found in the D-Area impoundment, which receives coal fly-ash. Trace metal body burdens and community composition were compared at the D-Area impoundment and reference sites. Stable isotopes of carbon and nitrogen were also analyzed to determine trophic linkages and the potential for transfer of contaminants in the impoundment. A laboratory experiment was used to separate direct uptake (contact with sediments and water) from trophic interactions as a means of contaminant entry for a representative aquatic vertebrate predator. Mosquito fish were subjected to four treatments: contaminated sediment and contaminated food, contaminated sediment and uncontaminated food, uncontaminated sediment and contaminated food, and uncontaminated sediment and uncontaminated food. While microcrustaceans and worms displayed some of the highest densities of invertebrates sampled at D-Area, they along with coleopterans, molluscs, odonates and Chaoborus were significantly reduced in density compared to the reference site. Spatial variation of invertebrate abundances within the D-Area impoundment was associated with patterns of water flow through the impoundment and submerged aquatic vegetation. Within the D-Area impoundment, biota consistently accumulated Cd, Se and Sr; body burdens of these contaminants were associated with concentrations in sediment. Stable isotope data showed a possible food chain consisting of Myrica, the amphipod Hyalella and mosquitofish (Gambusia holbrooki ). Contaminant levels of As, Se, Sr and Cu increased from Myrica to amphipods, but not from amphipods to mosquitofish. Nickel concentrations did not increase from Myrica to amphipods, but do increase from amphipods to mosquitofish. Our feeding trial showed that of the metals accumulated, the most important contributing factor was exposure to sediment. Selenium was the only metal that showed prey as a source of metal accumulation.