Predicting the Bioavailability of Metals and Metal Complexes: Critical Review of the Biotic Ligand Model

Vera I. Slaveykova; Kevin J. Wilkinson

doi:10.1071/EN04076

REVIEW

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Predicting the Bioavailability of Metals and Metal Complexes: Critical Review of the Biotic Ligand Model

Vera I. Slaveykova ^A and Kevin J. Wilkinson ^B ^C

+ Author Affiliations

- Author Affiliations

^A Environmental Chemistry and Ecotoxicology Laboratory (ENAC-ISTE-CECOTOX), Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.

^B Analytical and Biophysical Environmental Chemistry (CABE), University of Geneva, 1211 Geneva 4, Switzerland.

^C Corresponding author. Email: Kevin.Wilkinson@cabe.unige.ch

Vera Slaveykova is a Swiss National Science Foundation Professor and currently group leader in the Environmental Chemistry and Ecotoxicology Laboratory of the EPFL in Lausanne, Switzerland. Her research is in the field of environmental chemistry of aquatic and terrestrial systems. It is focussed on improving our understanding of the important phenomena controlling the transfer of trace elements and their interactions with different natural components such as biopolymers and microorganisms.

Kevin Wilkinson is interested in ‘molecular’ environmental chemistry. Current projects include the examination of the main physicochemical processes influencing trace metal bioaccumulation by microorganisms. The influence of the natural biopolymers on environmental processes, including flocculation and trace metal speciation are also of great interest. Various single molecule detection techniques are currently being used to characterize biopolymers, colloids and biological effects. He is a member of the Editorial Board of Environmental Chemistry.

Environmental Chemistry 2(1) 9-24 https://doi.org/10.1071/EN04076
Submitted: 17 November 2004 Accepted: 21 January 2005 Published: 21 March 2005

Environmental Context. The chemical speciation of trace metals greatly influences their biological effects. Nonetheless, no clear consensus currently exists as to when metal complexes are bioavailable, especially for field conditions. Recently, the USA EPA has incorporated the biotic ligand model (BLM) into their regulatory framework and many other countries are now examining the implications of following suit. This review examines the fundamental basis of the BLM in order to provide the reader with an understanding of its potential uses and limitations.

Abstract. The biotic ligand model is a useful construct both for predicting the effects of metals to aquatic biota and for increasing our mechanistic understanding of their interactions with biological surfaces. Since biological effects due to metals are always initiated by metal bioaccumulation, the fundamental processes underlying bio-uptake are examined in this review. The model assumes that the metal of interest, its complexes, and metal bound to sensitive sites on the biological surface are in chemical equilibrium. Therefore, many of the equilibrium constants required for the model have been compiled and their methods of determination evaluated. The underlying equilibrium assumption of the BLM is also examined critically. In an attempt to identify which conditions are appropriate for its application, several documented examples of failures of the BLM are discussed. Finally, the review is concluded by identifying some important future research directions.

Keywords. : bioavailability measurement — contaminant uptake — metals — thermodynamics

Acknowledgements

The authors thank the European framework BIOSPEC project (EVK1-CT-2001–00005) and the Swiss National Science Foundation (200020–101788 and PP002–102640) for providing funding directly related to this work. Critical reviews of a previous draft of the manuscript by E. Alasonati, F. Allienne, G. Batley, P. G. C. Campbell, T. Jaccard, C. Lamelas, D. Simon, J. Thevenaz, I. Worms, and three anonymous reviewers were extremely helpful as were discussions with J. Buffle and H. P. van Leeuwen.

References

Predicting the Bioavailability of Metals and Metal Complexes: Critical Review of the Biotic Ligand Model

Acknowledgements

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