Quantifying the structure of very small (<25 nm) natural aquatic colloids

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Natural aquatic colloids are defined as solid phase material between the sizes of 1 nm and 1 um (10^-9 / 10^-6 m) in size and are thus extremely small and finely divided with very large surface areas. They are ubiquitous in the aquatic (and terrestrial) environment and composed of different types of material such as organic (humic substances and polysaccharides), inorganic (metal oxides) and biological (viruses and bacteria) and these phases are mixed together in complex ways. We know that colloids chemically and physically bind trace pollutants such as metals and that these metals such as mercury, cadmium, nickel etc., may be toxic. In addition, we know that these colloids affect trace metal fate and behaviour and control metal transport and bioavailability. Further, it is known that the very small fraction (less than approximately 25 nm) is very important in metal binding under many environmental conditions and plays a defining role in bioavailability. Despite this knowledge which is primarily qualitative rather quantitative, there is a great deal that remains unknown in this area. In particular, our knowledge of 'nano-colloidal' (< ca 25 nm) structure is poor and improving our knowledge base here is essential to further understanding trace element chemistry, transport and bioavailability. This project aims to address some of these uncertainties by validating a methodology coupling flow field-flow fractionation (FlFFF) and atomic force microscopy (AFM) to quantify the shape of nanocolloids and their permeability (to solute and solvent molecules). Information about these structural measures can be contained within a simple ratio, usable in further modelling studies on speciation and bioavailability are essential to better fundamental understanding of the environmental 'function' of nanocolloids in trace element behaviour. The area of investigation is analogous to research over the last century into the structure-function relationships of biological macromolecules such as proteins and genetic material.