Uncertainty analysis of the urinary excretion of plutonium.

A quantitative estimate of the uncertainty of the urinary excretion of plutonium predicted by available biokinetic models is provided. Urinary excretion is primarily considered here because the monitoring of internal contamination of plutonium mainly relies on measurements of activity in urine samples. A previous paper has identified the most significant transfer rates for urinary plutonium excretion following an acute intake. That analysis is used here as a screening method to reduce the number of model parameters to be considered. A log-normal distribution was assumed for the probability distribution of the model parameters. The spread of the values, represented by the geometric standard deviation (GSD), is explicitly calculated, as few indications of the range of variation of systemic transfer rates are available. Different values for the GSD were considered. Assuming a certain GSD for all the systemic rate constants, random values of the rates were generated (by means of a Monte Carlo simulation with a Latin hypercube sampling scheme) and the resulting predictions of urine bioassay measurements were calculated. The comparison of the mean and variance of the predictions with the available data from several studies performed on different subjects provides information about the GSD of model parameters that represents the intersubject variation of transfer parameters.