Implications of human nasal clearance studies for the interpretation of nose blow and bioassay sample measurements

The Smith-Etherington extrathoracic (ET) clearance model has been developed to describe clearance from the human nasal passage as observed for 1.5, 3 and 6 μm monodisperse particles inhaled by participants while sitting or at light exercise. Model parameter values have been determined for 22 sets of nasal clearance data, from which typical nasal clearance parameter values have been derived. In this investigation, the faecal excretion of 5 μm activity median aerodynamic diameter (AMAD) Type S ²³⁹Pu was calculated for three sets of model parameter values, i.e. typical values and those determined for two experiments that respectively exhibited particularly rapid and slow clearance. The study has shown that a greater fraction of material deposited in ET is cleared to the GI tract, and that this clearance takes place over a longer period than assumed by the Human Respiratory Tract Model for Radiological Protection. The study has also shown that deliberate nose blow sampling might potentially be developed to determine the order of magnitude of intakes.