Speciation of Actinides (Environmental, Food, Clinical, Occupational, Health) (The contribution will follow then the arrangement of the actinides in the periodic table.)

Outline
Actinides are the fourteen elements, which follow the element actinium in the periodic table of elements. The first three actinides uranium, protactinium and thorium can be found in the nature, the other elements are artificial elements. Most speciation studies are carried with actinides from thorium to curium. The elements uranium, neptunium and plutonium show a wide variety of oxidation states. In tetravalent oxidation state the solubility is very low. In this oxidation state the hydrolysis is the most important reaction.

All these elements are radioactive. Therefore special laboratories to handle these elements are necessary. The concentration range for speciation studies with actinides is below 1 x 10-5 M. Therefore several speciation techniques, mostly basing on laser induced methods, are developed. A short overview in these methods will be given.

For thorium and protactinium only few data are available. Thorium does only exist in tetravalent oxidation state. Hydrolysis and phosphate speciation will be described. Protactinium exists in the pentavalent oxidation state and forms a dioxy-cation.

Most data are available for uranium speciation. Uranium exists in four oxidation states. Uranium-(III) is only stable in non-aqueous environments and plays therefore no role in speciation studies. Under reducing conditions uranium-(IV) is formed. Speciation examples for hydrolysis, sulfate, phosphate and arsenate will be given. In aqueous solutions uranium?(V) disproportionates into uranium-(IV) and uranium-(VI). Hexavalent uranium exists only as dioxy-cation.
In a next section environmental aspects of the uranium-(VI) speciation will be described. Uranium is found in more or less high concentrations in anywhere in the environment. Speciation examples from mining and milling will be described.
Uranium speciation in plants (as example for the food chain) will be described.
Neptunium forms oxidation states from +3 to + 7. Np(III) is slightly oxidized to Np(IV). The most stable oxidation states are Np(IV) and Np(V), the latter also forms a dioxy-cation. As example for environmental speciation the speciation of Np(V) with humic substances will be quoted.
Plutonium has oxidation states from + 3 to + 6. The redox potentials between these oxidation states are close together, so one can often find several oxidation states existing together. Examples for speciation in environment (here as specials case the Oklo mine in Gabun and results of bomb tests will be included) are shown, clinical and health aspects should be discussed (Pu is one of the most toxic elements).
Americium and Curium form trivalent ions in solution. These elements are important in waste repositories. Speciation in concentrated salt solutions and in mineral (calcite) phases are important examples for speciation in natural environments.
Actinides higher than Curium show at least short half-life. The long living isotopes are Berkelium 247 (1400 y), Californium 251 (900 y) and Einsteinium 252 (1.24 y). Fermium, Mendelevium, Nobelium and Lawrencium as well as the transactinide elements have half-life less than 1 y. Due to the very low production rates most of these elements are less relevant in speciation chemistry. Berkelium is found to have two oxidation states (III and V). Only few data on chloride and sulfate speciation are available.