Measurements of trace metal concentrations, fluxes and bioavailability using DGT
- Lancaster Univ. (United Kingdom)
The technique of diffusive gradient in thin-films (DGT) provides an insitu means of quantitatively measuring labile species in aqueous systems. By ensuring that transport of metal ions to an exchange resin is solely by free diffusion through a membrane, of known thickness, {Delta}g, the concentration in the bulk solution, C{sub b} can be calculated from the measured mass in the resin, M, after time, t, by C{sub b} = M{Delta}g/Dst, where D is the molecular diffusion coefficient and s is the exposure surface area of the membrane. If a sufficiently thick ({minus}1 mm) diffusion layer is selected, the flux of metal to the resin is independent of the hydrodynamics in solution above a threshold level of convection. Deployment for 1 day results in a concentration factor of about 300, allowing metals to be measured at extremely low levels (4 pmol 1{sup {minus}1}). Only labile metal species are measured, the effective time of measurement, typically 2 min., being determined by the thickness of the diffusion layer. The measurement is independent of ionic strength (10nM to 1M). For Chelex-100 as the resin, the measurement is independent of pH in the range of 5 to 8.3, but a sub-theoretical response is obtained at pH < 5 where binding to Chelex is diminished. The application of DGT to the insitu measurement of trace metals in freshwater and seawater is demonstrated. Its more general applicability as a pollution monitoring tool is discussed. In sediments and soils it can provide direct measurements of fluxes from solid phase to pore water, allowing it to be used as a surrogate for bioavailability.
- OSTI ID:
- 218457
- Report Number(s):
- CONF-9511137-; ISBN 1-880611-03-1; TRN: IM9619%%178
- Resource Relation:
- Conference: 2. Society of Environmental Toxicology and Chemistry (SETAC) world conference, Vancouver (Canada), 5-9 Nov 1995; Other Information: PBD: 1995; Related Information: Is Part Of Second SETAC world congress (16. annual meeting): Abstract book. Global environmental protection: Science, politics, and common sense; PB: 378 p.
- Country of Publication:
- United States
- Language:
- English
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