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

Abstract: The radionuclides 210Po and 210Pb widely present in the terrestrial environment are the final long-lived radionuclides in the decay of 238U in the earth’s crust. Their presence in the atmosphere is due to the decay of 222Rn diffusing from the ground. The range of activity concentrations in ground level air for 210Po is 0.03–0.3 Bq m−3 and for 210Pb 0.2–1.5 Bq m−3. In drinking water from private wells the activity concentration of 210Po is in the order of 7–48 mBq l−1 and for 210Pb around 11–40 mBq l−1. From water works, however, the activity concentration for both 210Po and 210Pb is only in the order of 3 mBq l−1. Mosses, lichens and peat have a high efficiency in capturing 210Po and 210Pb from atmospheric fallout and exhibit an inventory of both 210Po and 210Pb 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 210Po and 210Pb 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 210Po and 210Pb in humans. The effective annual dose due to 210Po and 210Pb in people with high consumption of reindeer/caribou meat is estimated to be around 260 and 132 μSv a−1 respectively. In soils, 210Po 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 210Po 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 210Po is particularly high as the result of the direct deposition of 222Rn daughters from atmospheric deposition. Tobacco is a terrestrial product with high activity concentrations of 210Po and 210Pb. The overall average activity concentration of 210Po is 13 ± 2 Bq kg−1. It is rather constant over time and by geographical origin. The average median daily dietary intakes of 210Po and 210Pb for the adult world population was estimated to 160 mBq day−1 and 110 mBq day−1, corresponding to annual effective doses of 70 μSv a−1 and 28 μSv a−1, respectively. The dietary intakes of 210Po and 210Pb from vegetarian food was estimated to only 70 mBq day−1 and 40 mBq day−1 corresponding to annual effective doses of 30.6 μSv a−1 and 10 μSv a−1, respectively. Since the activity concentration of 210Po and 210Pb 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. [Copyright &y& Elsevier]