3- Field and experimental studies of biological, physical and chemical factors controlling trace element circulation
 


 




CABE is involved with several field or simulated field studies in which the long-term goal is to contribute to the understanding of the mechanisms which control the circulation and bioavailability of vital and detrimental elements and compounds in aquatic systems (water, sediment, soil). Because natural organic matter (NOM) is implicated in essentially every reaction in the natural environment, much of our recent research has concentrated on the role NOM may play in some of the important  processes  which occur in the natural freshwaters. For example, although it is well established that NOM plays a key role in the circulation and bioavailability of trace elements, quantitative predictions of the effects of NOM in a given ecosystem are presently impossible, because the specific properties of NOM are poorly understood or even totally unknown. For example, the formation rate and structure of the aggregates depends on the nature (size, conformation, chemical reactivity) of the organic macromolecules present in the system of interest. At least two types of organic macromolecules play very different (sometimes opposite) roles in lakes: the soil-derived fulvics (small highly charged macromolecules; Mw~1000) and the water-borne polysaccharides (large macromolecules; Mw>10000). The processes of interest to our group are schematised in Figure 1:
 


Figure 1: Schematic representation of some of the important processes
determining metal bioavailability and transport


 



Research which is now underway examines some of the different roles of NOM in the natural environment by attempting to relate macromolecular structure to function in freshwater systems.

This research includes :

THE CHARACTERISATION OF NATURAL ORGANIC MATTER USING NON-PERTURBING TECHNIQUES

For several years, we have been developing techniques which allow the characterisation of NOM by transmission electron microscopy. Novel techniques are now being developed which will allow the separation, characterisation and study of interactions of NOM components under relatively non perturbing conditions. For example, the morphological characterization of organic macromolecules by atomic force microscopy (AFM) is now well underway.  Fluorescence Correlation Spectroscopy (FCS) is being developed in order to determine how solution physicochemistry affects the conformation and transport of NOM while Capillary Electrophoresis (CE) is being used to relate the structure of different components to their electrophoretic mobility and their ability to bind metallic pollutants. These techniques are complemented by voltammetric, size distribution (PCS) and ultracentrifugation techniques in order to characterise as completely as possible the NOM based upon its size and morphology.


THE ROLE OF NOM COMPLEXATION ON METAL BIOAVAILABILITY

Although bioavailability-chemical speciation relationships have been well-studied with simple synthetic complexants such as EDTA, the role of natural complexing macromolecules with complicated structures, like fulvic or humic compounds, is poorly understood; published results are, for the most part, contradictory or qualitative. Two novel techniques have been developed in our laboratories for measurements of trace metal speciation in the presence of complexing ligands: gel-covered voltammetric microelectrodes (GCVM), and the supported liquid membrane (SLM). These techniques are presently being exploited for the determination of trace metal bioavailability to aquatic microorganisms in the presence of humic and fulvic compounds.


THE ROLE OF NOM IN COLLOID AGGREGATION /  FLOCCULATION AND SEDIMENTATION

We will continue to examine how the interactions of large NOM macromolecules influence the aggregation of small inorganic colloids under field and simulated field conditions.
 
 


Figure 2: Aggregate of natural organic matter and small inorganic colloids (Bar represents 500nm)
 

Figure 3: Hard-working graduate student (A. Jozroland) during field study on Lake Bret.


Further information:

Determination of the conformation of natural organic macromolecules using atomic force and transmission electron microscopy

Roles of the various organic biopolymers in environmental processes in aquatic systems

Characterization of organic biopolymers using novel applications of fluorescence spectroscopy

Trace metal bioavailability to aquatic microorganisms in the presence of humic substances

Mechanisms determining trace metal bioavailability to aquatic microorganisms

The AFM page

Related recent publications:

S.E.J. Buikx, M.A.G.T. van den Hoop, R.F.M.J. cleven, J. Buffle and K.J. Wilkinson. 2000. Particles in natural surface waters : Chemical composition and size distribution. Intern. J. Environ. Anal. Chem. 77, 75-93.

K.J. Wilkinson and F. Cuenod. 2000. Optimization of the hydrolysis of freshwater polysaccharides. Intern. J. Anal. Chem. 77, 323-335.

J. Lead, K.J. Wilkinson, E. Balnois, C. Larive, B. Cutak, S. Assemi and R. Beckett. 2000. Diffusion coefficients and polydispersities of the Suwanee River Fulvic acid. Comparison of fluorescence correlation spectroscopy, nuclear magnetic resonance, flow field-flow fractionation and atomic force microscopy. Environ. Sci. Technol. 34, 3508-3513.

E. Balnois, S. Stoll, K.J. Wilkinson, J. Buffle, M. Rinaudo and M. Milas. 2000. Conformational transformation of succinoglycan as observed by atomic force microscopy. Macromolecules. 33, 7440-7447.

N. Mirimanoff and K.J. Wilkinson. 2000. Regulation of Zn accumulation by a freshwater Gram-positive bacterium (Rhodococcus opacus). Environ. Sci. Technol. 34, 616-622.

J. Lead, Wilkinson, K.J., Starchev, K., Canonica, S. and Buffle, J. 2000.  Diffusion coefficients of humic substances as determined by fluorescence correlation spectroscopy: Role of solution conditions. Environ. Sci. Technol. 34, 1365-1369.

X. Gayte, D. Fontvieille and K.J. Wilkinson. 1999. Bacterial stimulation in mixed cultures of bacteria and organic carbon coming from river and lake waters. Microbiol. Ecol. 38, 285-295.

E. Balnois, K.J. Wilkinson, J.R. Lead and J. Buffle. 1999. Atomic force microscopy of humic substances. Effects of pH and ionic strength. Environmental Science and Technology, 33, 3911-3917 (abstract)

K.J. Wilkinson, E. Balnois, G.G. Leppard and J. Buffle. 1999. Characteristic features of the major components of freshwater colloidal organic matter revealed by transmission electron and atomic force microscopy. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 155, 287-310 (abstract)

  J.R. Lead, E. Balnois, M. Hosse, R. Menghetti and K.J. Wilkinson.  1999. Characterization of Norwegian natural organic matter : size, diffusion coefficients and electrophoretic mobilities.   Environ. Int. 25, 245-258 (abstract)

  J. Buffle, Wilkinson K.J.,  Stoll S.,  Filella M. and  Zhang J. 1998. A generalized description of aquatic colloidal interactions:  The 3 colloidal component approach. Environ. Sci. Technol. 32, 2887-2899 (abstract)

P.H. Santschi, Balnois E., Wilkinson K.J., Zhang J., Buffle J. and Guo L. 1998. Fibrillar polysaccharides in marine macromolecular organic matter, as imaged by atomic force microscopy and transmission electron microscopy. Limnol Oceanogr. 43, 896-908 (abstract)


Person to contact:
 

Kevin Wilkinson

Address :
CABE
Department of Analytical Chemistry 
Sciences II, 30 Quai Ernest Ansermet 
CH-1211 Geneva- 4, Switzerland

  (41) 22 702 6051 

    (41) 22 702 6069 

Kevin.Wilkinson@cabe.unige.ch


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