Analysis of the uncertainty in internal dose estimate resulting from biological stochastic variability of excretion

A method for investigating the uncertainty in internal dose estimate resulting from biological stochastic variability of excretion is proposed in the paper. The method is based on analysing generated cases of individual monitoring data using Monte Carlo simulation technique. In case of a single intake and assumption of stochastic variability of excretion is a single source of uncertainty it was shown that the intake (dose) uncertainty depends exclusively on the uncertainty of the bioassay data and the number of daily urine (faeces) measurements. Assuming a log-normal distribution for describing the variability of excretion a simple expression for calculating the uncertainty was proposed. In case of routine monitoring data it was shown that the uncertainty of annual intake (dose) estimate would depend on biological stochastic variability of excretion, type of excretion function and the number of monitoring intervals in a year. By the example of Pu and U aerosols it was shown that the effects of decreasing uncertainty in the dose estimate resulting from increasing the number of monitoring intervals in a year and from decreasing the uncertainty of bioassay data (performing a number of successive daily measurements, once in a year) should be estimated to optimise the routine monitoring program.