The physicochemical forms in which a metal exists (i.e., its speciation) determine its mobility, bioavailability and toxicity in the environment. The significance of natural organic matter (NOM) in determining trace metal speciation in aquatic systems has long been recognised. The heterogeneous nature of these ligands provides an effective buffer for metal ion concentrations and as such is essential for the maintenance of life. However, despite an enormous number of studies, many unresolved aspects remain.
I have been working intermitently on this problem for 20 years. As a result, I am now even less inclined to recommend to any potential reader/user any of the ready-to-use models available than I was 25 years ago. Nevertheless, the problem remains an important and interesting problem. My work has tackeld different aspects
- initial research was performed under the supervision of Jacques Buffle and partly in collaboration with Scott Altmann: it consisted in the development and application of a continuous binding function approach (DEF and SODF); this approach followed initial ideas developped by Gamble:
S. Altmann, J. Buffle, M. Filella and A. Tessier (1990) Complexation by natural heterogeneous compounds. II. Site Occupation Distribution Functions, a normalized description of metal complexation. GEOCHIM. COSMOCHIM. ACTA, 54, 1535-1553 (1990).
Buffle, R.S. Altmann and M. Filella (1990) The effect of physico-chemical heterogeneity of natural complexants. II. The buffering action and role of their background sites. ANAL. CHIM. ACTA, 232, 225-237.
J. Buffle and M. Filella (1990) Physico-chemical heterogeneity of natural complexants: Clarification. ANAL. CHIM. ACTA, 313, 144-150 (1995).
J. Buffle, M. Filella and R.S. Altmann (1995) Polyfunctional description of metal complexation by natural organic matter: theory and practice. In: Binding models concerning natural organic substances in performance assessment. Nuclear Energy Agency, OCDE, Paris, pp. 149-161.
- application of the DEF concept to the voltammetric study of trace metal binding by humic substances; this work benefited from the initial collaboration of Herman van Leeuwen and was later performed in collaboration with Raewyn Town:
M. Filella, J. Buffle and H.P. van Leeuwen (1990) The effect of physico-chemical heterogeneity of natural complexants. I. Voltammetry of labile metal-fulvic complexes. ANAL. CHIM. ACTA, 232, 209-223.
M. Filella and R. Town (2000) Determination of metal binding parameters for humic substances. Part 1. Application of a simple calculation method for extraction of meaningful parameters from reverse pulse polarograms. J.ELECTROANAL. CHEM., 485, 21-33.
M. Filella, van Leeuwen, J. Buffle and K. Holub (2000) Voltammetry of chemically heterogeneous metal complex systems. Part II. Simulation of the kinetic effects induced on polarographic waves. J. ELECTROANAL. CHEM., 485, 144-153.
R. Town and M. Filella (2000) Determination of metal binding parameters for humic substances. Part 2. Utility of ASV pseudo-polarography. J. ELECTROANAL. CHEM., 488, 1-16.
- reinterpretation of published data for trace metals - NOM binding by following the DEF conceptual approach: this work has its roots in preliminary analysis performed in the early 80's by Jacques Buffle; the idea was extended to other elements and, more importantly, to other types of NOM and was performed in close collaboration with Raewyn Town
R. Town and M. Filella (2000) A comprehensive systematic compilation of complexation parameters reported for trace metals in natural waters. AQUATIC SCIENCES, 62, 252-295.
M. Filella and R.M. Town (2001) Heterogeneity and lability of Pb(II) complexation by humic substances: practical interpretation tools. FRESENIUS J. ANAL. CHEM., 370, 413-418.
R.M. Town and M. Filella (2002) Implications of natural organic matter binding heterogeneity on understanding lead(II) complexation in aquatic systems. SCI. TOTAL ENVIRON., 300, 143-154.
R.M. Town and M. Filella (2002) Crucial role of the detection window in metal ion speciation analysis in aquatic systems: the interplay of thermodynamic and kinetic factors as exemplified by nickel and cobalt. ANAL. CHIM. ACTA, 466, 285-293.
M. Filella and R.M. Town (2003) Implications of natural organic matter binding heterogeneity on understanding trace metal complexation in aquatic systems. J. PHYS. IV FRANCE, 107, 479-482 (2003).
M. Filella and R.M. Town (2005) A framework for interpretation and prediction of the effects of natural organic matter heterogeneity on trace metal speciation in aquatic systems. In: Environmental Chemistry. Green Chemistry and Pollutants in Ecosystems, E. Lichtfouse, J. Schwarzbauer and D. Robert (Eds.). Springer-Verlag, pp. 121-132.
- the inclusion of the DEF approach in a general speciation code; unfortunately the know-how, tools and funding have never been available and only a first preliminary study was possible:
C. Huber, M. Filella and R.M. Town (2002) Computer modelling of trace metal ion speciation: practical implementation of a linear continuous function for complexation by natural organic matter. COMPUTERS & GEOSCIENCES, 28, 587-596.