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Title: Biospec: Development and applications of the Donnan Membrane Technique

Primary Researcher: Erwin Kalis
Email address: erwin.kalis@wur.nl
Submitted on: September 11, 2002

Introduction:

Heavy metals in soils and water can be taken up by plants and soil micro-organisms and they can leach towards the ground water. Therefore it is important to get insight in metal concentrations occurring in (pore) water and their vulnerability for leaching. In (pore) water metals can be present (1) as "free" metal ions, (2) in complexes with inorganic anions and/or (3) adsorbed to dissolved organic matter. Availability of the metals for soil organisms, including plant roots, depends largely on the free metal ion concentration and not on the total metal concentration. This free metal concentration can be determined using the DMT (Donnan Membrane Technique), a speciation measurement technique which has been developed in Wageningen University.

Aim:

BIOSPEC will determine reliable and predictive quantitative parameters for assessment of the biouptake potential of trace heavy metals (Cu, Pb, Cd, Zn, Ni) by development of robust well-characterised sensors, which can be deployed routinely in situ by institutes monitoring water quality. This is a significant advance over any existing methodologies that typically involve extensive sample preparation and multi-step analyses, resulting in various operationally defined fractions that are often meaningless or empirical at best. To achieve this objective, a systematic approach will be adopted in which well-defined simple ligands, isolated natural ligands, soil solution samples and natural freshwaters are analysed in parallel by a range of analytical techniques in conjunction with metal biouptake studies.

Research:

The Donnan Membrane Technique contains a continuous flow system, in which the donor side and the acceptor side of the DMT cell are continuously flushed with solution across the membrane. The cell allows reaching pseudo equilibrium for the free metal ions via Donnan Equilibrium across a negatively charged ion-exchange membrane within a reasonable time span. The donor solution contains both free and complexed metal ions. The concentration of the cations in the acceptor solution is either equal to the concentration of the free cation concentration in the donor solution, or it can be calculated using simple correction factors. At this moment aqueous solutions are tested, among others in a biouptake experiment in with Lolium perenne is exposed to heavy metals.