Technical Report 122

Clearance classes

The International Commission on Radiological Protection (ICRP) recognised the impact of particle solubility on their toxicological profile. ICRP considered solubility and dissolution rate in its human respiratory tract dosimetry model (HRTM). Assuming that AM-derived clearance of particles in the deep lung was constant for a given species, the first HRTM (ICRP 1979) proposed three default clearance classes with different biosolubility (class D for t1/2 < 10 days; class W for t1/2 between 10 and 100 days; class Y t1/2 > 100 days, t1/2 was referred to pulmonary clearance in human). In the second model (ICRP 1994) absorption classes were introduced (class F; M and S). The classification is linked to default constants for calculating the dose and clearance of a respective radioactive particles. As ICRP recommended the clearance classes to assess internal dose of inhaled radiation, it is reasonable to employ the existing solubility classes in course of assessing the toxicological potential of particular matter. In the following table, clearance classes in line with recommendations of ICRP are proposed. A few examples are listed, and described in details as case studies.table1_not600