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Politics : Depleted Uranium -- Ignore unavailable to you. Want to Upgrade?

To: maceng2 who wrote (9)	9/28/2003 3:35:38 PM
From: maceng2	Read Replies (1) \| Respond to of 55

What Happens to Depleted Uranium Inside the Body? -------------------------------------------------- NRPB > FAQ > Depleted Uranium > nrpb.org -------------------------------------------------- Inhaled DU particles may enter the body through the nose and/or the mouth. Depending on their sizes, some particles will be exhaled, some will deposit in the upper airways (the nose, mouth and bronchial tree), and some will deposit in the deep lungs. Most particles larger than a few micrometres (µm) in diameter are filtered out in the upper airways and so do not reach the deep lungs: the nose is quite an effective filter. (One µm is one-thousandth of a millimetre. The cells that make up the body are typically about 10 µm across). Most particles that deposit in the upper airways are trapped in mucus that moves to the throat and are swallowed within a few hours. Most particles that deposit in the deep lungs are quickly captured by mobile cells called macrophages, rather similar to white blood cells. They may move the particles to the bronchial tree, to be carried away in mucus and swallowed, but this is a slow process, and some particles may remain in the lungs for years. A very small fraction of particles deposited in the lungs will be transferred to lymph nodes, where they would probably remain if they did not dissolve. However, whether in lungs or lymph nodes, uranium oxide particles will gradually dissolve, and the dissolved uranium will be absorbed into the blood. Even materials generally regarded as 'insoluble' will generally dissolve to some extent in the lungs: particles small enough to deposit there have a large surface area per unit mass for the liquids inside cells to work on. It is generally found that when dusts are inhaled and deposit in the lungs, a fraction of the material dissolves rapidly and the rest at a fairly steady rate. Tests have been carried out on DU oxides which simulated dissolution in the lungs. These showed that for the particles formed when lumps of DU are heated in a fire, a few percent dissolves rapidly, but the rest very slowly. For the particles formed when a DU penetrator impacts on armour plate, a larger fraction, about 25%, dissolves quickly. Other tests have shown that in both situations, the particles consist mostly of two uranium oxides (U3O8, with some UO2) both of which are relatively insoluble. Experiments carried out on industrial forms of these oxides indicate a long-term dissolution rate in the lungs of the order of 0.1% per day. When uranium compounds are ingested, uranium is not readily absorbed into blood from the gut. Even for soluble forms of uranium only a few percent is absorbed (2% is usually assumed for radiation protection purposes). For the uranium oxides formed from DU impacts or fires, the fraction is likely to be much less. For relatively insoluble compounds like the two oxides above, in workplaces, 0.2% is usually assumed. Most of the uranium absorbed into blood is rapidly excreted, mainly in urine. About 65% is excreted during the first day, another 10% during the rest of the first week. There is a continuing slow excretion, about 0.002% of the original uptake to blood per day after a year. That is why measurements are often made on urine to estimate the amount of uranium in the body. The uranium that is not rapidly excreted deposits in various organs. In particular, about 10% deposits in the kidneys. Since the kidneys are relatively small (about 300 g> in an adult), the concentration will be higher than in other organs. However, most of the uranium deposited in the kidneys does not stay for long. By 3 months, the amount retained is only about 0.1% of the original uptake to blood. About another 15% deposits in bone, but since the mass (5000 g) is much greater than that of the kidneys, the concentration is lower. Uranium does stay much longer in the bone, so there will still be a few percent left after 5 years, and about 1% after 25 years.