Polonium-210 and lead-210 in the terrestrial environment: a historical review

The radionuclides Po-210 and Pb-210 widely present in the terrestrial environment are the final long-lived radionuclides in the decay of U-238 in the earth's crust. Their presence in the atmosphere is due to the decay of Rn-222 diffusing from the ground. The range of activity concentrations in ground level air for Po-210 is 0.03-0.3 Bq m(-3) and for Pb-210 0.2-1.5 Bq m(-3). In drinking water from private wells the activity concentration of Po-210 is in the order of 7-48 mBq l(-1) and for Pb-210 around 11-40 mBq l(-1). From water works, however, the activity concentration for both Po-210 and Pb-210 is only in the order of 3 mBq l(-1). Mosses, lichens and peat have a high efficiency in capturing Po-210 and Pb-210 from atmospheric fallout and exhibit an inventory of both Po-210 and Pb-210 in the order of 0.5-5 kBq m(-2) in mosses and in lichens around 0.6 kBq m(-2). The activity concentrations in lichens lies around 250 Bq kg(-1), dry mass. Reindeer and caribou graze lichen which results in an activity concentration of Po-210 and Pb-210 of about 1-15 Bq kg(-1) in meat from these animals. The food chain lichen-reindeer or caribou, and Man constitutes a unique model for studying the uptake and retention of Po-210 and Pb-210 in humans. The effective annual dose due to Po-210 and Pb-210 in people with high consumption of reindeer/caribou meat is estimated to be around 260 and 132 mu Sv a(-1) respectively. In soils, Po-210 is adsorbed to clay and organic colloids and the activity concentration varies with soil type and also correlates with the amount of atmospheric precipitation. The average activity concentration levels of Po-210 in various soils are in the range of 20-240 Bq kg(-1). Plants become contaminated with radioactive nuclides both by absorption from the soil (supported Po) and by deposition of radioactive fallout on the plants directly (unsupported Po). In fresh leafy plants the level of Po-210 is particularly high as the result of the direct deposition of Rn-222 daughters from atmospheric deposition. Tobacco is a terrestrial product with high activity concentrations of Po-210 and Pb-210. The overall average activity concentration of Po-210 is 13 +/- 2 Bq kg(-1). It is rather constant over time and by geographical origin. The average median daily dietary intakes of Po-210 and Pb-210 for the adult world population was estimated to 160 mBq day(-1) and 110 mBq day(-1), corresponding to annual effective doses of 70 mu Sv a(-1) and 28 mu Sv a(-1), respectively. The dietary intakes of Po-210 and Pb-210 from vegetarian food was estimated to only 70 mBq day(-1) and 40 mBq day(-1) corresponding to annual effective doses of 30.6 mu Sv a(-1) and 10 mu Sv a(-1), respectively. Since the activity concentration of Po-210 and Pb-210 in seafood is significantly higher than in vegetarian food the effective dose to populations consuming a lot of seafood might be 5-15 fold higher. (C) 2011 Elsevier Ltd. All rights reserved.