Deposition and Retention of Inhaled Cerium

The ICRP Task Group on Lung Dynamics (ICRP, 1966) also reviewed the available literature and developed a model to describe the clearance of materials from the respiratory tract to the gastrointestinal 

Clearance of particles from the nasopharynx to the gastrointestinal tract is predicted by the model to occur with a 15 min half-time for 

Class Y-Avid Retention cleared slowly (years) 

Class W-Moderate Retention intermediate clearance rates (weeks) 

Class D-Minimal Retention rapid clearance (days) 

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Fig. 17. Biological model recommended for describing the uptake and retention of cerium by humans after inhalation or ingestion. Numbers in parentheses give the fractions of the material in the originating compartments which are cleared to the indicated sites of deposition. Clearance from the pulmonary region results from competition between mechanical clearances to the lymph nodes and gastrointestinal tract and absorption of soluble material into the systemic circulation. The fractions included in parentheses by the pulmonary compartment indicate the distribution of material subject to the two clearance rates however, these amounts will not be cleared in this manner if the material is previously absorbed into blood. Transfer rate constants or functions, S(t), are given in fractions per unit time. Dashed lines indicate clearance pathways which exist but occur at such slow rates as to be considered insignificant compared to radioactive decay of the cerium isotopes.

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