Plutonium-238 (238Pu) has a half-life of about 87.7 y and thus a higher specific activity than 239Pu. It is used in
radioisotope thermoelectric generators and is a substantial source of
plutonium alpha-radiation in spent nuclear fuels. Early animal studies demonstrated differences in the biokinetics of inhaled
oxides of 238Pu and 239Pu with 238Pu having a substantially more rapid translocation from the lungs to the systemic organs, particularly the skeleton. This resulted in the predominant occurrence of skeletal
cancers in animals exposed to 238Pu
oxides but
lung cancers in those with exposures to 239Pu
oxides. The anatomical distribution of
osteogenic sarcomas seen in animal studies was similar to that observed with 239Pu and also in
plutonium workers but differed from naturally occurring
tumors. The in vivo "solubility" of 238Pu has been associated with the relative amounts of 238Pu/239Pu in the particles and calcination temperatures during the preparation of the dioxides. There is experimental evidence of in vivo 238Pu particle fragmentation attributed to nuclear recoil during radioactive decay. The resulting conversion of microparticles to nanoparticles may alter their interactions with macrophages and transport across epithelial barriers. There are few documented cases of human exposures, but the biokinetics appeared to depend on the chemical and physical nature of the
aerosols. Robust human biokinetic and dosimetric models have not been developed, due in part to the lack of data. With the acceleration of nuclear technologies and the greater demand for reprocessing and/or disposal of spent nuclear fuels, the potential for human exposure to 238Pu will likely increase in the future.