Predictive approach to speciation

In this section, the term 'speciation' will be taken to mean the chemical form of the element or substance, including the oxidation state, charge and complexation properties. The behaviour of trace elements in natural systems, especially those displaying multiple valence states, is known to be critically dependent on speciation, hence the attention devoted to this subject in the context of environmental protection and waste management. However, consideration of speciation is not limited to these particular fields. The principal situations to which this document pertains are: - Performance assessment of a repository for radioactive waste; - Decommissioning of nuclear facilities. - Land remediation activities following unintentional and/or unregulated release of radioactive materials. Methods for determining speciation are numerous and greatly exceed those considered in the present discussion. The scope of the report will be restricted to the actinide elements, although the principles could be adapted to include other radioactive materials and toxic metals. Organic compounds are considered only in regard to their role in actinide chemistry, notably metal-organic complexation and the formation of organic colloids. Three main categories are recognised: - Metallo-organic materials that have been disposed of or accidentally released; - Naturally occurring high molecular weight organics (humic and fulvic acids); - Degradation products of, for example, cellulose that have the potential to bind actinide ions. The following sections address the various approaches available for acquiring speciation information. This does not constitute an exhaustive review but rather the intention is to provide a working outline for addressing the prediction of speciation. (author)