Identification of plutonium retention parameters in humans via pharmacokinetic analysis of occupational plutonium urinary excretion data

The urinary excretion database built up at Sellafield since the early 1950s was made available for analysis as part of a research programme into plutonium biochemistry. A set of cases was selected for which the data were adequate to support analysis based on a standard pharmacokinetics approach. Cases include exposures from both inhalation and wound deposition, and from plutonium nitrate, oxalate and metal. Data sets extended from 12 years post-exposure up to 25+ year post-exposure. The pharmacokinetics approach was found to be valuable, calling into question certain aspects of ICRP methodology and highlighting areas where further research is required. In particular, it suggested that the distribution equilibrium phase, reached within 3 to 4 years post-exposure, was followed by a terminal equilibrium phase with a half-life of some 12 years. This long-term half-life, which was much shorter than those in ICRP models, persisted for over 20 years in some cases. (author)