Speciation 98: Abstracts

Biota like bacteria and algae are ubiquitous in natural waters and their cell walls show a strong affinity for a wide variety of metal cations. This is understandable thinking of the variety of surface functional groups of these cell walls, including amino, carboxylic, hydroxyl, thio and phosphate sites.

In order to be able to interpret toxicity, bioavailability, transport and deposition of trace metals a more detailed understanding of the different uptake processes is required.

Recently, some results have been published (1,2,3) showing how the adsorption of metal ions to algal and bacterial surfaces can be described by chemical equilibrium models similar to those for hydrous mineral surfaces. The customary way to represent reactions at these surfaces has been through equilibria of the type:

=SOH + Me2+ =SOMe+ + H+	(1)
=SOH + Me2+ =SOMeOH + 2H+	(2)
2=SOH + Me2+ (=SO)2Me + 2H+	(3)

The degree of protonation depends on the acid-base equilibria

=SOH + H+ =SOH2+	(4)
=SOH =SO- + H+	(5)

Equilibria (1) to (5) can be described by charge dependent stability constants according to the "surface complexation" concept.

Different models for metal adsorption onto surfaces of algae and bacteria will be presented and discussed.

References

1. Xue, H-B., Stumm, W: and Sigg, L. The binding of heavy metals to algal surfaces. Wat.Res.1988,22,7,917-926.
   
2. Knauer, K., Behra, R. and Sigg L. Adorption and uptake of copper by the green alga Scenedesmus Subspicatus. J. Phycol. 1997,33,596-601.
3. Fein, B. F., Daughney, C. J., Yee, N. and Davis, T. A. A chemical equilibrium model for metal adsorption onto bacterial surfaces. Geochi. Cosmochim. Acta, 1997,61,3319-3328.

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