The biological behaviour and toxicology of plutonium and transplutonics

Abstract

The biological behaviour of plutonium and transplutonics depends upon the physico-chemical properties of the incorporated radionuclide and upon biological factors. They can enter the body either by inhalation, by ingestion or through wounds. Inhalation is the most likely route of accidental intake in workers, while ingestion can be considered as the pathway to the general population from discharges to the environment due to routine or accidental releases. All the transuranium elements translocated from the site of entry by the circulating blood are deposited in the same tissues and organs; they accumulate in two major organs, bone and liver, both of which represent more than 90% of the activity cleared from the blood. Acute and medium-term effects are due to very high radiation doses which would only occur in extreme accidental situations. The level of activity deposited in the lung after inhalation of plutonium which will cause death of half of an exposed population within a few months is evaluated around 3.7 MBq (100 μCi). The main delayed effect is the development of cancer, which has been demonstrated in experimental animals, and which occurred mainly in the lung and in the skeleton. Those effects have been observed at levels much greater than those likely to be encountered in man. The frequency of lung cancers following inhalation of actinides increases with the dose up to a maximum and then decreases at higher doses as a result of cell sterilization and death. No evidence of hereditary effects resulting from the incorporation of actinides in the gonads has been demonstrated in any of the animal species studied. There are no data on the development of cancers in human as a result of incorporation of plutonium or any transplutonic. Estimates of risk have therefore been based on the results of epidemiological studies on humans exposed to external radiation, and on some available information on the development of bone and liver cancers as a result of intakes of other alpha emitters. At present the methods for removing accidental intakes of plutonium and transplutonics from the body are moderately successful. For removing the transportable forms, the administration of the chelating agent DTPA is presently the recommended method. If insoluble forms are inhaled, bronchopulmonary lavage is the only effective treatment.