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Home | Did You Know?Polonium ContaminationAccording to NCRP Report No. 65, Management of Persons Accidentally Contaminated with Radionuclides (1980), 210Po was used extensively in early atomic weapons manufacture and later was employed briefly in thermoelectric generators in space satellites. The first communications satellite was powered by a 210Po source. Polonium-beryllium neutron sources have now largely been replaced by plutonium-beryllium or transplutonic sources. Polonium-210 is used as a static eliminator (Robertson and Randle, 1974) in a variety of applications. Polonium, element number 84, is a soft silvery-gray metal, much like lead in appearance. It volatilizes readily in a vacuum at elevated temperatures. When deposited on Pyrex glass or quartz, it eventually produces small irregular cracks called crazing (Goode, 1956). Therefore, old polonium ampoules should be considered hazardous. Polonium readily forms halides and many polonium compounds are relatively soluble. The atmosphere normally contains polonium. It arises from radiurn-226, which occurs widespread in nature in Earth's crust (Hill, 1965). Contributions have been added by such man-made activities as burning fossil fuels, nuclear weapons testing in the atmosphere, and accidents such as the Windscale reactor accident. Grazing animals take up 210Po from contaminated grass and concentrations greater than 37 Bq kg–1 have been found in caribou in the Arctic (Hill, 1965). Marine organisms ranging from plankton to shellfish, crabs and fish (Hoffman et al., 1974) are often contaminated with 210Po. Cigarettes have been found to contain approximately 0.018 Bq per cigarette (Hill, 1965) and it has been suggested as a possible cause of lung cancer (Marsden, 1964). Such information can be of some importance to the physician when he receives a bioassay report stating a low-level 210Po content that cannot be explained on the basis of an occupational exposure. Polonium-210, formerly called radium F, is the last radioactive member of the uranium-radium radioactive series and has therefore been extensively studied in uranium miners. After years of exposure, about 78 % of the polonium body burden will be found in the skeleton with important deposits in the lung, liver, muscle, lymph nodes, kidney, spleen, and blood (Blanchard and Moore, 1971). This distribution probably is derived more from the preceding isotopes in the chain than from 210Po itself. Polonium-210 decays by alpha emission with a physical half-life of about 138 d. The biological half-time in the whole body is about 40 d (ICRP, 1968), while for the spleen and kidneys it is somewhat longer, about 60 and 70 d, respectively (ICRP, 1960). The longest effective half-life, 46 d, is in the kidneys. The critical organs are considered to be the spleen and kidneys (ICRP, 1960). Studies on several species of laboratory animals have shown the highest concentrations of 210Po to be in kidney, ranging from 5 to 10 % of the injected radionuclide (ICRP, 1968). The metabolism of polonium chloride has been studied in terminal human cancer patients (Silberstein et al., 1950). After intravenous injection of 6.3 to 11.1 kBq kg–1, 210Po was eliminated in the feces at levels 10 to 20 times higher than in the urine. Polonium chloride is poorly absorbed from the intestine after ingestion. In one experiment, the daily absorption through the skin was found not to exceed 2 % of the amount applied. Two physicists who inhaled 210Po after the rupture of a polonium/beryllium source were observed to excrete 10 times more 210Po in the feces than in the urine (Foreman et al., 1958). Another contamination accident that occurred in a university print shop resulted from the cleaning of a device to eliminate static; in this incident the operators incurred no significant radiation exposures (Caruthers and Maxwell, 1971). Another small exposure was reported to have been due to accidental inhalation of 210Po during the handling of an encapsulated source (Scott and West, 1975). No treatment was required. Approximately 3 % of the 555 Bq burden was excreted in the urine with a biological half-time of 33 d. The initial fecal to urine ratio of 65 dropped to 20 about 20 d post-exposure. Dimercaprol has been suggested as a treatment (Hursh, 1951; 1952). When it was given intramuscularly after a single intravenous dose of 210Po, the total excretion in a 10 d period was twice that of the control animals and the polonium was shifted from the bone marrow, spleen, and testes into muscle. When rats were injected with a lethal dose of 210Po (1.33 MBq kg–1), the median survival time was 22 d, but when promptly treated with dimercaprol the median survival time was 89 d. The untreated animals died of hematopoietic failure, while much less effect was demonstrated on the white cell and platelet levels of treated animals. Russian investigators have reported some success with the use of dimercaprol derivatives in animal experiments, but the compounds are not available in the United States (Erleksova, 1959; Parfenov et al., 1974). Neither DTPA nor EDTA is effective in treating polonium internal contamination (Foreman et al.,1958). Get the full report and references at: http://NCRPpublications.org NCRP Report No. 65 is being updated by NCRP Scientific Committee 4-1, Management of Persons Contaminated with Radionuclides:
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