[Speciation of metals in occupational medicine]

The identification and quantification of elements as such (that make up the historical analytical method used in toxicological studies) are necessary but not sufficient, in all cases, to understand and evaluate the mechanism of interaction between elements and biological targets. In fact, in order to approximate the factors that control the concentrations of elements in environmental or biological media, we need to know the occurrence of species of the elements themselves. This is element speciation, i.e. the capability of separating, identifying and determining the species in which an element is present and/or transformed. There are few, although increasing in latter years, examples of element speciation able to confirm the importance of this research approach in toxicological studies. Some basic information from these studies have found specific application in selecting the most appropriate indicators and the most representative matrices for biological monitoring. Furthermore, element speciation provides additional and often essential information in evaluating metal toxicity. The toxicity of the three oxidation states of Mercury differ considerably. For arsenic, a decreasing order of toxicity arsenite > arsenate > monomethylarsonic (MMA) > dimethylarsenite (DMA) has been proposed. However, the use of speciation in investigating toxicokinetic aspects appears to be difficult to apply to many other metals, mainly due to the lack of information about the existence and significance of species whose determination would be worthwhile and to the lack of analytical methods enabling us to measure species in biological media. Nonetheless, the horizon for speciation is more extensive and less linear than expected since about 15 elements, 20 oxidation states, and 25 organic compounds have been just involved in speciation. Problems might arise for biological monitoring practices, and the following topics should be considered: (i) identification of species and determination of their concentration; (ii) knowledge about the specific (relevant) role in physiologic and pathologic processes in which the element is involved; (iii) availability of analytical methods responding to acceptable quality requisites; (iv) feasibility and ethics of sampling.