This seminar will feature Dr. Bruce Duncan with EPA's Region 10 - Office of Environmental Assessment - Risk Evaluation Unit, and Dr. Jim Shine Associate Professor of Aquatic Chemistry at Harvard University's Center for the Environment. Drs. Duncan and Shine will present their research on the "Gellyfish". The 'Gellyfish', an in-situ equilibrium-based sampling tool for determining multiple free metal ion concentrations in aquatic systems, has been developed and refined under both laboratory and field conditions. The device is based on the equilibrium partitioning between free metal ions in the surrounding solution and iminodiacetate binding groups held within the gel matrix of the sampler. Ninety percent equilibration (t₉₀) is achieved in approximately 26 hours. Apparent stability constants were measured for the binding of Cu, Zn, Pb, Ni, and Cd to the Gellyfish, allowing us to estimate their free metal ion concentrations in the surrounding solution. An accompanying computer model (GELLYMOD) was also developed to account for metal-metal competition for uptake into the sampler. Subsequent competition experiments involving two or three metals were performed to validate the computer model. The results suggested the use of the Gellyfish sampler, in conjunction with the model we developed, is a valid approach for accurately quantifying free metal ion levels in metal mixtures within environmentally relevant concentration ranges. Compared to other analytical methods for free metal ions, the Gellyfish sampler is inexpensive, rapid, reusable, easy to use, and can measure multiple metals simultaneously, thus permitting the generation of adequate quantities of data to examine spatial and temporal variability and other the factors affecting metal speciation.

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Live Online Class, Internet Based View details on CLU-IN   September 23, 2010 - September 23, 2010