Health Risks of Radon and Other Internally Deposited Alpha-Emitters BEIR IV (1988) / Chapter Skim
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3 Polonium
3 Polonium
Pages 159-175
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From page 159... ...
Echo and Echo are in the thorium-thoron decay chain. One reason for interest in the alpha particles from polonium is their existence as radon daughters; indeed, with respect to important radiation dose, the radon problem is due largely to polonium.
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From page 160... ...
Airborne radon decays into polonium isotopes that can be deposited on terrain and vegetation, for example, on tobacco leaves. Some have postulated that the alpha-particle radiation from polonium, volatilized from smoking tobacco, plays an important role in the genesis of lung cancer in smokers.37 PROPERTIES The chemical behavior of polonium was described many years ago by Haissinskyi~ i9 and others, later by Moyer,33 and in the Russian
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From page 161... ...
The nonaggregated form, although less striking autoradiographically, can account for a substantial fraction of the radiation dose. Polonium has less tendency to form specific complexes with biomolecules than do radium, plutonium, americium, or other transuranic elements, although relatively loose combinations with numerous moieties are common; for example, polonium combines with the gIobin portion of hemoglobin and other blood constituents and binds nonspecifically to proteins.
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From page 162... ...
Substantial radiation doses from polonium can be expected in many tissues of the body. Indeed, it supplies a more nearly wholebody dose than any other alpha-emitter except radon gag, but only by contrast to the highly localized doses imparted by bone seekers, such as plutonium and radium.
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From page 163... ...
Long-term pathologic developments are affected by differences in dosage regime.3 The presence of aggregates of polonium in tissues after parenteral administration raises the question of whether special account should be taken of the nominally much larger potential dose surrounding a large aggregate in a given tissue compared with the dose from a comparable amount of diffusely distributed polonium. Results of an investigation of the comparability of the "hot spots problem in bone and the "hot-particle~ problem for plutonium in the lungs seem to indicate that the diffuse pattern can be as effective or even more effective in carcinogenesis.
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From page 164... ...
The amounts of polonium bound to protein and in colloidal form are considered sufficient to account for its low urinary clearance rate. The role of the liver in removing polonium to the feces by the bile was confirmed in bile duct ligation experiments in animals by Finki3 and in the early work of Lacassagne summarized by Fink.
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From page 165... ...
In contrast, life shortening in the mouse by strontium-89 is much reduced if the dose is divided.~7 Indeed, the effect of beta particles from 89Sr is comparable with that of x rays and has been interpreted as being due to the presence of a much higher fraction of reversible injury caused by low linear energy transfer radiation. The increase in effectiveness caused by protraction of the dose from alpha particles, described elsewhere in this report, has not been seen with polonium.
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From page 166... ...
There was involution of growing cartilage, arteriolar nephrosclerosis, vacuolization of adrenal cortical cells, atrophy of the pancreas, hypoplastic and hyperplastic changes in pulmonary lymphoid tissue, obstructive pulmonary emphysema with partial oh struction of bronchioles, and general arterioscIerosis.6 Some of these changes were direct radiation effects; others were indirect degenerative sequelae. Nearly all these detailed histopathological findings have occurred at relatively high doses, well above those of primary interest in this report.
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From page 167... ...
Disturbances of protein and nucleic acid metabolisms and impairment of activity of the nervous system and the immune system were observed. HUMAN STUDIES PATIENTS AND WORKERS In the work of the Manhattan Project during World War IT and as part of the broad study of distribution and excretion of polonium, five patients hospitalized with lymphatic cancer or leukemia received tracer doses of polonium.~3 Excretion rates and partition between urine and feces in all five patients were comparable with those findings in animal experiments.
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From page 168... ...
Analysis of excrete indicated body burdens of 0.2-7 psi, which is far above the existing maximal permissible burden of 0.04 psi. Yet no noticeable changes in general health, blood, or kidney function were observed throughout a Month observation period.
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From page 169... ...
Holtzman22 calculated a dietary intake of 1.8 psi/day for a few otherwise unexposed subjects on an average American diet, and Hillel calculated 3.2 psi/day for six people in the United Kingdom. A more elaborate study of metabolic balances involved 12 unexposec!
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From page 170... ...
Ratios of 2~0Pb to Ammo were used to determine how long the insoluble particles from cigarette smoke remained on bronchial epithelium.38 Polonium contents of many plants were measured, and no large differences in initial contents were found. However, the 2~0Pb activity of tobacco was fixed on insoluble particles by the curing process.
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From page 171... ...
A risk evaluation based on radon daughter exposure is probably that of a risk based on the short-hal£life polonium isotopes. However, it would apply only to lung cancer, and it may or may not apply to the longer-lived Echo.
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From page 172... ...
The best candidate is probably a colloidal form of thorium dioxide caDed Thorotrast, because it seeks the reticuloenothelial system and delivers most of its alpha dose to the tissue of deposition, usually the liver. Risk estimates based on Thorotrast would be largely those for the development of liver tumors.
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From page 173... ...
Quarterly Report ANL 5247 of the Biological and Medical Division, Argonne National Laboratory. Also Progress Report, Design of Experiment and Survival Following Single Injection.
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From page 174... ...
1976. Polonium-210 lead-210 ratios as an index of residence times of insoluble particles from cigarette smoke in bronchial epithelium.
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From page 175... ...
1964. Mortality, life span and growth of rats with a maintained body burden of polonium.
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