Bones, uranium toxicity

Methods for Reducing Toxic Effects. Uranium forms complexes with the bicarbonate ion (Cooper et al. 1982) and has been administered prophylactically after uranium exposure (Fisher et al. 1991). Bicarbonate can alkalize the blood to a degree that facilitates the excretion of uranium via the kidneys. This in turn, can prevent uptake by and deposition in critical tissues (kidney, bone). Chelation has been tested in animals and found to have a limited potential, though possibly valuable, role in reducing acute uranium toxicity. Further research is needed to validate, refute, or refine method(s) for reducing the toxic effects of uranium compounds. No verified methods for reducing the toxic effects of long-term exposure to uranium are currently available. 

A study by the oral route establishing a threshold for renal effects in weanling and adult rats of the same strain is needed to determine if susceptibility to uranium toxicity varies with age. Histopathological studies and urinalysis should be performed, as well as measurement of uranium in excreta for both groups. At termination in this study, uranium content should be measured in tissues, particularly bone and kidney. This will provide information on whether retention of uranium in bone is age-dependent (as assumed by analogy with calcium in PBPK models) and on whether kidney burden associated with uranium toxicity is age-related. 

Animal studies indicate that the primary toxic effect of uranium exposure is on the kidney, with particular damage to the proximal tubules. Functionally, this may result in increased excretion of glucose and amino acids. Structurally the necrosis of tubular epithelium leads to formation of cellular casts in the urine. If exposure is insufficient to cause death from renal failure, the mbular lesion is reversible with epithelial regeneration. Although bone is the other major site of deposition, there is no evidence of toxic or radiocarcinogenic effects to bone or bone marrow from experimental studies. ... 

The human body also absorbs certain elements such as gold and aluminum from food, water, and air that are not useful but are also not dangerous in such tiny amounts. When the body absorbs more toxic elements such as uranium, lead, and cadmium, however, tiny amounts stored in the bones and liver can cause serious harm. 

The model was used to estimate uranium intakes uranium burdens in the lungs, kidneys, and bones and effective dose equivalent for each worker in the accident. Initial intakes of workers involved in the accident ranged from 470-24,000 pg uranium. The model estimated the maximum kidney concentrations in the workers as ranging from 0.048 to 2.5 pg U/g kidney tissue, renal toxicity was not observed in any of the workers (Fisher et al. 1990, 1991). 

In addition, the sequestration patterns of the different uranium compounds are important determinants for the target organ chemical and radiological toxicities of these compounds. The site of deposition for the soluble uranium compounds (uranyl nitrate, uranium tetrachloride, uranium hexafluoride) is the bone, while the insoluble compounds (uranium hexafluoride, uranium dioxide) accumulate in the lungs and lymph nodes (Stokinger 1953). 

A further possible reason for separating plutonium from uranium and the fission products relates to the extreme toxicity of Pu. Plutonium(IV) mimics iron(lll) (the aqueous E° and charge-to-radius ratios of the two ions are very similar), so that cancers are likely to result from the absorption of even microgram amounts of ingested radioactive Pu into organs of the human body (bone marrow, spleen, liver) that store iron(III). It may therefore be considered desirable to remove Pu, a long-lived health hazard, from spent nuclear fuels before disposal of the latter in repositories that may not remain inviolate for thousands of years into the uncertain future (most of the fission products decay away to negligible levels of activity in an acceptable time). 

The widespread use of radionuclides in the nuclear industry and in other areas of work, means that there is a risk that accidents involving the intake of quite large amounts of one or more radionuclides may occur. Some radionuclides, notably those of lead, strontium, the lanthanides, uranium, thorium, and plutonium are removed quite rapidly from the blood and deposited in bone, where they may be retained for many years. This deposition of non-physiological and potentially toxic... 

The greatest health risk from large intakes of uranium is toxic damage to the kidneys, because, in addition to being weakly radioactive, uranium is a toxic metal. Uranium expo.sure also increases your risk of getting cancer due to its radioactivity. Since uranium tends to concentrate in specific locations iti the body, risk of cancer of the bone, liver cancer, and blood diseases (such as leukemia) are increased. Inhaled uranium increases the risk of lung cancer. 

Plutonium is the most toxic substance known. It is a very dangerous radiological hazard and is specifically absorbed in bones and collected in the liver. For those reasons the element must be handled extremely carefully. Plutonium is produced in all uranium reactors according to the process in Figure 52.9. 

---