Basis for the ICRPʼs Age-specific Biokinetic Model for Uranium

Abstract

In an effort motivated largely by the Chernobyl nuclear accident, the International Commission on Radiological Protection (ICRP) is developing age-specific biokinetic models and dose coefficients for environmentally important radionuclides. This paper describes the ICRP's age-specific biokinetic model for uranium. The model is constructed within a physiologically based framework originally developed for application to the alkaline earth elements but sufficiently general to apply to the larger class of bone-volume-seeking elements. Transfer rates for a reference adult are based mainly on: 1. measurements of uranium in blood and excreta of several human subjects who were intravenously injected with uranium; 2. postmortem measurements of uranium in tissues of some of those subjects; 3. postmortem measurements of uranium in tissues of occupationally and non-occupationally exposed subjects; 4. data on baboons, dogs, and smaller laboratory animals exposed to uranium for experimental purposes; and 5. consideration of the physiological processes thought to control retention and translocation of uranium in the body. Transfer rates for the adult are extended to children by application of a set of generic assumptions applied by the ICRP to calcium-like elements. These assumptions were derived mainly from observations of the age-specific biokinetics of the alkaline earth elements and lead in humans and laboratory animals but are consistent with available age-specific biokinetic data on uranium.

Cancer Incidence and Mortality in Populations Living Near Uranium Milling and Mining Operations in Grants, New Mexico, 1950–2004

“…Cell division and regeneration occur in response to cell damage and death, resulting in enlargement and decreased kidney function. Heavy metal ions, such as uranyl ions, may also delay or block the cell division process, thereby magnifying the effects of cell damage (Leggett 1989(Leggett , 1994ATSDR 1999b).…”

Uncertainties in Cancer Risk Coefficients for Environmental Exposure to Radionuclides. An Uncertainty Analysis for Risk Coefficients Reported in Federal Guidance Report No. 13

“…Information on the systemic biokinetics of uranium comes from measurements of uranium in blood and excreta of several unhealthy human subjects who were intravenously injected with uranium; postmortem measurements of uranium in tissues of some of those subjects; postmortem measurements of uranium in tissues of occupationally and environmentally exposed subjects; data on baboons, dogs, or smaller laboratory animals exposed to uranium for experimental purposes; and consideration of the physiological processes thought to determine retention and translocation of uranium in the body (Leggett 1994, ICRP 1995a. Data from controlled studies on human subjects may not be typical because of their state of health or the fact that the subjects were administered relatively high masses of uranium, which may have altered the kinetics of uranium to some extent, particularly in the kidneys.…”

Controlling intake of uranium in the workplace: Applications of biokinetic modeling and occupational monitoring data

“…This is a generic model structure applied by the ICRP to several elements that tend to follow the movement of calcium in bone (Leggett 1992). Uranium is not a physiological analogue of calcium in most respects, but the uranyl ion follows the movement of calcium in bone sufficiently closely that the structure of the calcium model is applicable to uranium (Leggett 1994). There is evidence that UO 2 ++ exchanges with Ca ++ at the surfaces of bone mineral crystals, although UO 2 ++ apparently does not participate in crystal formation or enter existing crystals.…”

“…Most of the transfer coefficients in the model are element specific. Uranium-specific parameter values given in Table 3.4 were based mainly on the following sources of information: measurements of uranium in blood and excreta of several human subjects who were intravenously injected with uranium; postmortem measurements of uranium in tissues of some of those subjects; postmortem measurements of uranium in tissues of occupationally and environmentally exposed subjects; data on baboons, dogs, or smaller laboratory animals exposed to uranium for experimental purposes; and consideration of the physiological processes thought to determine retention and translocation of uranium in the body (Leggett 1994;ICRP 1995a). The methods of selection of the parameter values of the ICRP's systemic model for uranium are described by Leggett (1994).…”