Oceanography / Limnology
Numerical Modeling
Visualization and Animation
Specialized Sampling Tools
Acid Rock Drainage
Database/Software Development

Analyses of trace metal in natural waters typically include determinations of "dissolved" and "total" components. However, there has long been recognition that neither of these fractions provides a reliable indication of the concentration of metal that is harmful to aquatic life (the "bio-available" concentration). Nonetheless, due to lack of convenient cost-effective and field-friendly techniques for the measurement of bio-available metals, "dissolved" and "total" concentrations remain the benchmarks by which environmental evaluations are based.

Diffusive Gradients in Thin Films (DGT) overcomes many of the limitations associated with more traditional speciation techniques (e.g., polarography). DGT is an in situ water sampling device that has been developed to measure biologically-available metals in natural waters and effluents. The active mechanism involves the use of a polyacrylamide gel layer to quantitatively control the diffusive transport of metals to a cation exchange resin. The resin only adsorbs free and relatively-labile metal ions. Since metal bio-availability is related to the free-ion activity, the device provides a proxy for the biological-available metal fraction.

The main advantages of the DGT over existing sampling methodologies include:

  • DGT is designed for in situ use, which minimizes the risk of contamination during sample handling and transport to the laboratory;
  • There is no need for sample filtration since particulate metals are excluded by the sampler;
  • The volume of samples to be shipped to an analytical laboratory is reduced;
    Metals are fixed in situ thereby avoiding changes in speciation during transit to the laboratory;
  • The ability to easily archive samples for long-term storage thereby offsetting analytical costs;
  • Metals are concentrated in the resin and therefore ultra-low analytical detection limits are not required; and
  • The use of a cation exchange resin obviates matrix interferences for sampling in high ionic-strength media.