Polonium-210 in the bio-sphere : Bio-kinetics and biological effects

• Polonium-210 is an alpha particle emitting radioactive element with a half-life of 138 days. It appears at the end of the decay-chain of Uranium-238 where the long lived Lead-210 (22.3 a) decays to Bismuth-210, and finally Polonium-210. 210Po is introduced into the biosphere through various routes of terrestrial and marine radioecological pathways. The level of 210Po activity in drinking water (5 Bq.kg-1) and in most common food items of terrestrial origin are usually low (0.04-0.1 Bq.kg-1 wet mass) and considered to be without concerns for human health. In some terrestrial food items such as reindeer and caribou, high 210Po levels (10 Bq.kg-1 wet mass) are due to their habit of grazing lichens (250 Bq.kg-1 dry weight). The food chain lichen-reindeer and man in arctic and sub-arctic regions is a unique pathway of 210Po to man. The enhancement of 210Po concentrations is also very pronounced in marine organisms feeding upon phytoplankton at the base of the food chain. Fish and seafood therefore have high activity concentrations of 210Po (2-15 Bq.kg-1). The daily dietary intakes of 210Po vary widely around the world with an estimated average median of about 160mBq.day-1. That corresponds to annual effective doses of about 70μSv.a-1 for 210Po. Populations mainly living on reindeer meat or marine food have a 5-10 fold higher annual effective doses. High activity concentrations (13 ± 3 Bq.kg-1) of Po-210 and Pb-210 are found in tobacco and its products. The annual effective radiation dose from 210Po for the whole body of a smoker who smokes 20 cigarettes per day has been estimated to 400μSv.a-1. The concentrations of 210Po in the air-ways and the lung tissues caused by smoking of tobacco contributes to a high radiation adsorbed dose to the respiratory epithelium, which contribute to the increased incidence of lung cancer observed among smokers, In December of 2006, former Russian intelligence operative Alexander Litvinenko died by what proved to be ingestion of polonium-210. This incident brought with it an increased interest of the bio-kinetics and radio-toxicity of 210Po. Alpha particles have a greater relative biological effectiveness (RBE) than gamma and X-rays considering cancer induction. But there are still no significant proofs in terms of increased risk in humans of in vivo bystander effects of 210Po alpha particle radiation. More work has to been done in studying RBE and the mechanism of the bystander effect and its relevance to cancer induction in man.

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NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

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