Actinium, Radioactive

Exposure Summary

Actinium occurs naturally in association with uranium ores; however, concentrations present in uranium minerals are small. The estimated concentration of actinium in the earth's crust is 5.5X10-10 mg/kg. Mining of actinium from uranium ores is not feasible since actinium concentrations in these ores are very small; most actinium used today is artificially produced. Thirty-four isotopes and isomers of actinium are recognized and all are radioactive. Actinium-227 and actinium-228 are the only naturally occurring isotopes. Actinium-227 is the longest lived isotope of actinium, with a half-life of 21.77 years. Actinium compounds are ionic and would not be volatile and would exist solely in the particulate phase in the ambient atmosphere. Particulate-phase actinium compounds will be removed from the atmosphere by wet or dry deposition. Actinium ions would be expected to adsorb to soils, since actinide ions with III, IV, and VI oxidation states can be adsorbed to cation-exchange resins. Actinium is primarily found in its +3 oxidation state as either the oxide, hydroxide, or halide salt. Actinium compounds are ionic and would not volatilize from moist or dry soil surfaces. Actinium ions would be expected to adsorb to suspended particles in water, since actinide ions with III, IV, and VI oxidation states can be adsorbed to cation-exchange resins. The predominant oxidation state of actinium is +3, and this would be the oxidation state most likely present under environmental conditions. Since actinium compounds are ionic, they will not volatilize from water surfaces. Bioconcentration is not expected to be an important fate due to the ionic nature of actinium compounds. Since actinium has only been produced in limited quantities and has limited commercial uses, exposure to actinium compounds would be limited to individuals involved in the production of actinium or its use in research. (SRC)
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