PARENT SESSION
26 - Metal Pollution: From Exposure to Ecological Effects (1)
8:30 AM to 12:20 PM, Tuesday, 14 May 2002
Session Chair: Janssen, Colin ¹, Gerhardt, Almut ¹, ¹ .
Strauss C

(26-03) An in situ kinetic probe for metal speciation and bioavailability in waters, soils and sediments.

Zhang, Hao^*,1, Scally, Shaun¹, Davison, William¹, ¹ Department of Environmental Sciences, IENS, Lancaster, United Kingdom

ABSTRACT- Biological uptake of metals depends on the relative importance of the transfer kinetics across the cell membrane compared to the rate of mass transport and the dissociation rate of metal complexes in waters and/or the desorption rate of metal bound to the solid phase in soils and sediments. The understanding of the kinetics of metal release from its binding agent (ligand or particle) in relation to bioavailability has been hampered by the lack of simple, realistic procedures to determine the rates and extent to which metals can be released and supplied to biota. The emerging technique of diffusive gradients in thin-films (DGT), where ions diffuse through a gel to a binding resin, may overcome these difficulties and provide a simple tool for kinetic characterisation in situ. DGT's potential as a kinetic probe is illustrated by measurements on well-defined solutions of metals and ligands. The dissociation rate constants of metal complexes were determined within the DGT lability detection window. Size-based discrimination for labile inorganic measurement can be achieved by varying the composition of the gels so that they impede to different extents the diffusion of large molecules. The DGT measurement in soils and sediments, expressed as effective concentration, embraces the concentration in solution phase, metal resupplied from solid phase and its kinetic characteristics. Evidence so far has indicated that DGT measurements represent bioavailable metals, where the uptake is controlled by diffusion and resupply. DGT provides an integrated measurement, accommodating the main factors that may affect metal bioavailability. Hence it may be a useful chemical surrogate for assessing bioavailable metals in waters, soils and sediments.

Key words: DGT, metal speciation, kinetic constants, bioavailability