Characterization of the Chemical Lability and Bioavailable Fraction of Heavy Metals in Natural Waters Using In-Situ Diffusion Gradient in Thin-Film (DGT) Probes.EPA Grant Number: R828162
Title: Characterization of the Chemical Lability and Bioavailable Fraction of Heavy Metals in Natural Waters Using In-Situ Diffusion Gradient in Thin-Film (DGT) Probes.
Investigators: Moffett, James W.
Institution: Woods Hole Oceanographic Institution
EPA Project Officer: Lasat, Mitch
Project Period: June 1, 2000 through May 31, 2002
Project Amount: $224,949
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry
Description:A semi-permeable membrane device for in situ passive sampling of heavy metals has been developed. We propose to study metal accumulation on these devices in model systems and natural waters. Initial findings show that only chemically labile, and biologically available, forms of heavy metals such as Cu, Zn, Cd and Pb will accumulate on the probe. The objectives are to confirm that probes provide quantitatively useful data about dissolved phase speciation that are consistent with other methods, and to show that they can be deployed in the field to study variability in metal chemistry in complex aquatic systems.
Approach:Comparative measurements using the probes and electrochemical methods will be conducted in the laboratory and in Boston area harbors and rivers to establish the relationship between dissolved phase speciation and metal uptake by the probes. Copper is a priority, since there is current interest in determining the bioavailability of this highly toxic element to derive water effects ratios and develop site specific criteria. Silver will also be a high priority, as a tracer of municipal discharge. Probes will be deployed during episodic input events such as storms and dredging to evaluate the usefulness of the probes in providing a time-integrated signal to record pulses which may be missed with discrete sampling. We also wish to advance our fundamental knowledge of diffusional processes into the gel, in order to determine which complexes actually accumulate within the probes, and to investigate alternative materials for the probes that might make them more selective for specific complexes.
Expected Results:Quantitative relationships between the accumulation of heavy metals in the probes and independent measurements of free metal ion concentration, the inorganically complexed and labile fractions will be established for Cu, Cd, Pb, and Zn in a wide range of water types. Deployments during episodic input events will reveal the their effects on bioavailable metal levels and their spatial and temporal variability. Multi-element capability will be evaluated by analysis of additional elements such as Ag by ICP-MS.
Improvements in Risk Assessment and Risk Management:
Probe data will be useful in developing site specific water criteria and waste load allocation models, and may become a low cost, highly sensitive complement to toxicity testing for routine monitoring. Deployment of many probes in aquatic systems is feasible because of low cost per unit (<$100) and ease of analysis (by atomic absorption spectroscopy for many metals), providing important information about metal bioavailability in aquatic systems subject to complex input and mixing processes. Episodic input events associated with combined sewage overflows and other facilities can be more accurately monitored with in situ devices than by discrete sampling.