Uranium transfer in the food chain from soil to plants, animals and man

In the 16-km-thick Earth's crust, 2.4–3.2 mg uranium/kg is assumed to occur. Thus, uranium is more abundant than iodine, cadmium or selenium. In Central Europe, the vegetation richest in uranium is found on granite weathering soils. Compared to these, the uranium content of the flora is about 25% less on Muschelkalk soils, ∼50% less on Buntsandstein, Keuper weathering soils and gneiss weathering soils, and more than 50% less on Pleistocene sands.Drinking water from Pleistocene sands often contains only 1–10% of the uranium content found in that from granite. Mineral and medicinal waters in Germany contain between <0.015 and 25 μg U/L. In all, 39% of the mineral waters analysed store <0.10, 29% 0.10–0.99, 15% 1.0–4.9 and 17% 5–25 μg U/L, with 2% of them containing <10 μg U/L.The majority of the extremely uranium-rich mineral waters are coming from Thuringia, the adjoining states Hesse, Saxony-Anhalt, and especially from the Black Forest in Baden-Württemberg. The high uranium contents there are delivered to the mineral waters and the food chain by the granite in the subsoil of these areas.Compared to control plants, wild and cultivated plants from the immediate vicinity of uranium waste dumps were found to store normal to eightfold uranium contents. Leafy plants species accumulated much uranium, whereas tubes, thick parts of stalks, fruits and grains stored less uranium. With increasing age of the vegetation, its uranium content decreases significantly.The uranium content of 116 foodstuffs and beverages varies extremely. Vegetable foods accumulate between 0.8 μg U/kg dry matter (DM) in margarine, bee honey and pearl barley, 50 μg U/kg DM in asparagus, and >100 μg U/kg DM in mixed mushrooms. As a rule, sugar-, starch- and fat-rich foodstuffs proved to be uranium-poor (fruits, seeds, flour), whereas leafy vegetables, tea and herbs can be uranium-rich.Animal foodstuffs accumulate lower uranium contents, with 0.7 μg U/kg DM in butter and 1.1–1.9 μg U/kg DM in condensed and normal cow's milk, 1.5–3.1 μg U/kg DM in pork, beef, chicken and mutton, 3–10 μg U/kg DM in fish, and 16 μg U/kg DM in hen's eggs. Prepared food for babies and young children proved to be uranium-poor. However, its uranium content can increase to 50 times that of mother's or cow's milk due to its preparations with particularly recommended mineral water that is rich in uranium.Of the uranium ingested by adults, 41% are delivered through beverages, 33% through vegetable and 26% through animal foodstuff.Since the end of the GDR and the reunification of Germany, the uranium intake by adults slightly increased from 2.2 to 3.0 μg U/day in men, and from 2.2 to 2.6 μg U/day in women. It varied considerably from region to region due to geological effects. The test population on the Pleistocene formation in Northern Germany only took in one third of the uranium amounts taken in Thuringia. Uranium does not accumulate in the body.The apparent absorption rate (7 days) amounted to about 6%, which is extremely high.The uranium content of drinking and mineral waters needs to be publicly controlled.