Future developments and requirements

Standardisation of speciation schemes - Despite the significant advances that have been made in metal speciation measurement techniques over the past 30 years, much remains to be done. The methods that have been developed do not provide an absolute breakdown of metal species, but rather operationally defined classifications. Because of this operational nature, the standardisation of the procedures becomes essential if different results are to be compared. So far, this has rarely been achieved. 

Development of new in situ analytical methods for species determination - There is a disparity between the amount of speciation information obtained from laboratory studies on well-defined systems, and that which is applicable to the real environmental situation (Buffle, 1990). Development of in situ methods will facilitate more relevant measurements which minimise perturbation of the system. Systems particularly prone to measurement-induced artefacts include anoxic waters, the sediment-water interface and colloidal materials. Methods for accurate measurement of free metal ion concentration over a much broader concentration range than that currently available are particularly required. 

Improvement of the chemical characterisation and quantification of organic materials - As already mentioned, the NOM found in freshwaters is composed of an extremely complex mixture of compounds, most of which (80%) are not yet identified. Moreover, in the case of thoroughly studied homologous groups, such as fulvic and humic matter, scant attention has been paid to the identification of the nature of minor sites, which are probably more relevant for trace metal control than 

Study of the behaviour and properties of colloidal and particulate matter - Improvement of the measurement techniques currently available, particularly in the submicrometre range, as well as development of the theory necessary to describe the interactions between small colloids and organic matrices is needed. New techniques such as AFM or fluorescence correlation spectroscopy may give information on the conformation characteristics of such molecules as well as their adsorption and aggregation properties. 

Study of the role played by living organisms in trace metal control - A considerable number of laboratory-based studies have been done on the response of aquatic organisms to trace element perturbations, mainly in relation to toxicity. However, studies utilising organisms relevant to environmental systems and conducted under realistic environmental conditions are urgently needed. Mechanisms used by organisms to control the external chemical medium are mostly unknown. 

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This chapter will start off by giving a historical overview of the use of EPXMA/CC-SEM/EDX and TW-EPXMA applied to environmental particles, concentrating on airborne particulate matter. The more recent advances where TW-EPXMA is combined with MRS and ATR-FT-IR-IT to elucidate the chemical and structural nature of airborne particulate matter will then be discussed. The few examples where airborne particulate matter has been analysed by SEM/EDX interfaced with MRS (SEMSCA, illustrated in Fig. 1) will be summarised and the chapter will conclude with a view of potential future developments and requirements for further extensions to current practices. 

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