Development of an In Situ Method for the Detection of Bioavailable Trace Metals in Sediments

Andrew Huisman
Hope College

Trace metals are collected quantitatively when the technique Diffusive Gradients in Thin Films (DGT) is used in situ in lake sediment, reducing the problems inherent in collecting and transporting sediments to a laboratory for metals analysis. For a given temperature, the metal ion flux through a diffusive gel of known thickness can be calculated. After diffusion, ions are bound in a chelating layer of iminodiacetic acid. Metals ions adhering to the chelating gel can be measured via Inductively Coupled Plasma (ICP) spectrometry after elution with acid. The measured amount of metal bound to the gel is proportional to the bulk concentration of labile metal ions in the sediment porewater. In undisturbed sediment, historical depositions of metals may be observed as band of heightened concentration in the DGT chelating gel. We have adapted commercial chelating discs to this novel detection technique, where the metal ion concentration bound to the disc can be measured directly via Proton Induced X-ray Emission (PIXE) spectrometry. The advantage of PIXE analysis over ICP analysis is higher spatial resolution and significantly quicker analysis. Preliminary results from the cross comparison of these techniques plus a demonstration of its utility in measuring metals in the environment will be presented.