Health Risk Evaluations for Ingestion Exposure of Humans to Polonium-210

Abstract

ᮀ The incident in London during November 2006 involving a lethal intake by Mr. Alexander Litvinenko of the highly-radioactive, alpha-particles-emitting polonium-210 (Po-210) isotope, presumably via ingestion, sparked renewed interest in the area of Po-210 toxicity to humans. This paper is the result of assembling and interpreting existing Po-210 data within the context of what is considered a reliable risk model (hazard-function [HF] model) for characterizing the risk of death from deterministic effects of high alpha radiation doses and dose rates to body organs. The HF model was developed to address radiation exposure scenarios involving combined exposures to alpha, beta, and gamma radiations and can be used in circumstances where only one type of radiation is involved. Under a plausible but not yet validated set of assumptions and using available megabecquerel (Po-210) to gray dose-conversion factors, acute lethality risk vs. dose curves were developed for circumstances of ingestion exposure to Po-210 by humans. Initial risk calculations were carried out for a reference adult male human (a hypothetical 70-kg person). Results were then modified for application to all ages (except the in utero child) via the use of systemic Po-210 burden. Because of the unavailability of acute lethality data derived from human ingestions of high levels of Po-210, plausibility of risk calculations were evaluated based on data from studies of Po-210 injections in animals. The animal data, although limited, were found to be consistent with the theoretical risk calculations. Key findings are as follows: (1) ingestion (or inhalation) of a few tents of a milligram of Po-210 will likely be fatal to all exposed persons. (2) Lethal intakes are expected to involve fatal damage to the bone marrow which is likely to be compounded by damage caused by higher doses to other organs including the kidneys and liver. (3) Lethal intakes are expected to cause severe damage to the kidney, spleen, stomach, small and large intestines, lymph nodes, skin, and testes (males) in addition to the fatal damage to bone marrow. (4) The time distribution of deaths is expected to depend on the level of radioactivity ingested or inhaled, with deaths occurring within about a month after very high levels of radioactivity intake (e.g., systemic burdens > 1 MBq/kg-body-mass) and occurring over longer periods, possibly up to or exceeding a year for lower but lethal intakes (systemic burdens from 0.1 to 1.0 MBq/kg-body-mass). Below a systemic burden estimate of 0.02 MBq/kg-bodymass, deaths from deterministic effects are not expected to occur but the risk of cancer and for life shortening could be significant. New, funded experimental and modeling/theoretical research is needed to improve on these estimates.

Calculating Pulmonary-Mode-Lethality Risk Avoidance Associated with Radionuclide Decorporation Countermeasures Related to a Radiological Terrorism Incident

“…Calculating pulmonary-mode lethality risk avoidance Equation 3 was developed for exposure to low LET beta and/or gamma radiation but was also applied to high-LET alpha radiation via adjusting model parameters (Scott 2007) or via using RBE-weighted dose (Scott and Peterson 2003). For the pulmonary mode of death (radiation pneumonitis and fibrosis related) and for internal low-LET beta/gamma radiation, central estimates for HF model parameters are V = 5, θ ∞ = 10 Gy, and θ 1 = 30 Gy 2 /h (Scott and Hahn 1989).…”

Radionuclide exposure in animals and the public health implications

“…This is a double whammy because grazing animals in particular are directly affected by consumption of forage/ feed contaminated by lead (either airborne or absorbed by plant roots), resulting in impaired erythrogenesis and central nervous system dysfunction (39). Moreover, acute lethal doses of 210 Po can cause fatal damage to the bone marrow and severe damage to the kidneys, spleen, and gastrointestinal tract (40).…”

“…For instance, 210 Po, an alpha-particle emitter, is one of the most toxic substances known because of its intense radioactivity and is therefore classified as a Group I human carcinogen (42,52). Concentrations as low as 1 µg have an activity of 1.66 × 10 8 Bq, and acute lethal doses may cause severe damage to the bone marrow, kidneys, spleen, digestive tract, and reproductive system (40,41). The preference therefore of important radionuclides for certain organs/ tissues for bioaccumulation may serve as an informational tool in making dietary choices, in which case, consumption of organs that tend to accumulate radionuclides may be avoided.…”

The Polonium-210 Public Health Assessment: The Need for Medical Toxicology Expertise in Radiation Terrorism Events

“…The events of November 2006, however, stimulated and reinvigorated worldwide interest in this relatively obscure element, and those events prompted the authoring of many new articles in the literature about its toxicity and the public health response to this event [16][17][18][19][20][21][22][23][24]. Articles concerning the "biological behavior" of this element have expanded our knowledge about its potential use as a poison.…”