9406373 Benoit Silver is one of the most toxic metals in the aquatic environment, yet, because of past contamination artifacts, there are currently no reliable data on its concentration, transport, and fate in fresh waters. Based on lab experiments that simulate estuarine conditions, silver at moderate levels can be directly toxic to plankton and invertebrates while low levels can influence estuarine community structure and reduce bivalve growth rates. Fresh waters, having more silver sources and less complexation by chloride than do estuaries, are likely to have an even greater problem with silver toxicity. Silver's naturally low abundance means that it may derive almost entirely from anthropogenic sources, and can serve as a non-degradable tracer of pollution, free from obfuscation by natural background concentration variations. An equally important reason to study silver is that it is one of the few pure class B metals, and as such, its study can help to delineate one end of the total range of metal behavior. At present the aquatic chemistry of silver is poorly understood. Because of the almost complete lack of reliable information on freshwater silver, this proposal is designed as a reconnaissance to explore the biogeochemical context of silver cycling and to position researchers for more detailed studies of specific processes in the future. The research comprises three main components: 1) to initiate establishment of benchmark Ag levels in freshwater, 2) to identify and quantify natural and anthropogenic sources, and 3) to specify and begin to investigate processes and mechanisms that control silver's transport, bioavailability, and fate. The research will use ultra-clean methods to avoid contamination artifacts that have plagued nearly all previous studies on trace metals in fresh waters. An important goal is to prompt additional freshwater studies that use these methods. The investigation will be conducted along the entire length of the once highly- industrialized Quinnipiac River, including a mid-stream lake. A mass balance approach will be used, providing the opportunity to compare natural, point, and nonpoint sources of silver, and to quantify removal rates. Based on preliminary measurements, headwaters of the Quinnipiac are extremely clean, while the lower river is badly contaminated. Two other rivers, the Naugatuck and Connecticut, will be studied in less depth in order to increase the generality of the findings within the constraints of a modest budget. Of these two, the Naugatuck has a history of severe metal pollution, while the Connecticut does not. Techniques that will be used are: 1) conventional membrane filtration (to separate particulate and non-particulate fractions), 2) ultrafiltration (for colloidal forms), 3) anodic stripping voltammetry (to appraise silver -organic matter complexes), 4) thermodynamic calculations (to estimate dissolved ion speciation), 5) measurement of pore water (to evaluate diffusive flux from sediments), and 6) Ag concentration and 210Pb geochronology of sediments (to assess resuspension fluxes and document contamination history).
