Uncertainties in doses due to the number of aerosol particles: study on 239PuO2 using default parameters for workers

The behavior of individual particles has been taken into account to estimate, after inhalation, uncertainties in deposition fractions and doses due to the number of 239PuO2 aerosol particles. Using ICRP models and default parameters recommended for workers, similar results were obtained after calculation and after simulations of exposures to 500 to 3 x 10(6) particles (from about 1 Bq to 6 kBq). Uncertainties obtained from simulations increase as the number of particles decreases. The maximal uncertainties in the deposition fraction were observed for the sequestered regions in which no deposit often occurs for exposures of less than 1 x 10(5) particles. Similar large uncertainties in the number of nuclear disintegrations over 50 years were observed in the sequestered regions as well as in lymph nodes. For a given number of particles, uncertainties in committed equivalent doses gradually decrease from the extra-thoracic region to lymph nodes, bronchi, bronchioles, and alveolar interstitium. For 1 x 10(4) particles, similar uncertainties were observed for the committed equivalent doses delivered to lung, liver, bone surfaces, red marrow and gonads, and for dose per unit intake (DPUI), whereas for 1 x 10(5) particles and more, uncertainties in DPUI were higher than those in equivalent doses. The explanation is that in some simulations the maximal committed equivalent dose was delivered to the extra-thoracic respiratory tract region (in which case the DPUI calculation mode must be changed).