Implementation of an In Vitro Experimental Setup Simulating Pulmonary Dissolution Following the Inhalation of Radioactive Particulate Material

Given the need for criteria to control the radiation doses due to radionuclide inhalation, in 1994 the International Commission on Radiological Protection presented a classification for radioactive compounds based on their pulmonary absorption rates. The Commission classified the compounds into fast, moderate, and slow categories and assigned to each material a default absorption class. Nevertheless, the proposed categories do not always resemble the actual behavior of the classified materials in the pulmonary environment. Therefore, the Commission itself suggested the assessment of the inhalation risk of a particulate substance referring to an in vivo study using the same material. Since it is not possible to trace in literature in vivo studies analyzing the physiological behavior of the totality of inhalable radioactive materials, the Commission suggested adopting in vitro systems simulating the pulmonary mechanism. For this reason, in the last 50 y, many simulating setups have been implemented, but none of these seemed to reproduce the lung dissolution dynamics effectively as the results were not comparable with the ones obtained using in vivo techniques. This paper aims to describe an innovative experimental apparatus implemented as an attempt to add another step toward the realization of a gold standard. In particular, the system was validated with BaSO 4 particulate, and the resulting error with respect to the physiological expected value figured as less than 4%. The system was then employed for the lung dissolution tests of radioactive graphite extracted from Politecnico di Milano's nuclear reactor to assess the radiobiological risk due to a slow lung absorption process that workers might run into during the reactor decommissioning.