Americium in the Beagle Dog: Biokinetic and Dosimetric Model

Abstract

A biokinetic model of the systemic distribution of americium in the beagle dog is presented. The model is based on a previous biokinetic model of plutonium. The data sets used for the development of the model were the measurements of excreted activity (urine and feces) and organ burdens (skeleton, liver, and other soft tissues) for different levels of initial injected activity. In developing the model, the compartmental structure of the skeleton of the plutonium model was adopted, and only the numerical values of parameters were adapted. The model well describes the fractions of americium in the skeleton, liver, and soft tissues and the total fraction excreted in urine and feces. The tuning of the liver clearance parameter provides a realistic description of the change in the partitioning between liver and skeleton for different injection levels. The most significant features of the biokinetics and dosimetry of americium and plutonium in beagles are compared. The total fractions of the clearance to the skeleton and the liver are roughly equal to the value for plutonium, but the partitioning of americium between these organs is reversed with respect to the partitioning of plutonium. 241Am doses to liver and skeleton are similar to 239Pu doses, owing to some counteracting factors. For the highest injection level, the liver mass is dependent on the time post injection. For the skeletal tissues, the dose to the cortical endosteum by far exceeds the dose to the trabecular endosteum and the red marrow. The model provides the basis for statistical survival analyses and risk estimates.

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

“…Publication 71 (ICRP, 1995b) provided a brief review of the literature relating to inhaled americium compounds in the context of the HRTM, and with emphasis on forms to which members of the public might be exposed as a result of environmental releases. (864) Reference biokinetic models were used here (i.e. by the Task Group) for analysis of the data and determination of absorption parameter values: the HRTM (ICRP, 1994a, 2015), the Gastrointestinal Tract Model (ICRP, 1979a), the HATM (ICRP, 2006), the human systemic model for americium (ICRP, 1993), the americium model for the dog of Luciani et al. (2006), the rat model for particle transport in the respiratory tract of the Guide for the Practical Application of the ICRP Human Respiratory Tract Model (ICRP, 2002), and the function describing the whole-body retention of injected americium in the rat from Ménétrier et al.…”

Absorption of americium compounds in the respiratory tract

“…Their faecal excretion was assumed to follow the gastro-intestinal tract model or alimentary tract model of ICRP (1979ICRP ( , 2006 with an intestinal absorbed fraction of 5  10 4 (ICRP 1994b). The dog Am model of Luciani et al (2006) was applied to systemic behaviour and excretion. For rodents, the extra-pulmonary retention and excretion was modelled by a two-exponential function described by Ménétrier et al (2008).…”