Toxicity of Uranium

The three main exposure pathways to uranium compounds are through the diet, inhalation, or injury, as described earlier. The uptake of uranium after ingestion is affected mainly by soluble uranium compounds (insoluble compounds are excreted through feces with little or no hazardous health effects) as discussed earlier. However, for inhaled compounds, the chemical and physical characteristics determine how long the uranium will be retained in the lungs and what fraction will enter the bloodstream during a given time period. The common practice is to divide these compounds into 

FRAME 4.2 THE DISPUTE ABOUT THE HEALTH EFFECTS OF EXPOSURE TO DEPLETED URANIUM 

Depleted uranium is probably one of the chanical substances with the worst public relations record, as a very cursory Google search shows (all accessed on March 8, 2014). Some of the titles Depleted uranium as malicious as Syrian chemical weapons. Depleted uranium contamination is still spreading in Iraq, Depleted uranium The real dirty bombs, and Depleted uranium—/ar worse than 9/11 Depleted uranium dust—public health disaster for the people of Iraq and Afghanistan, are just a few examples. However, the evidence-based scientific literature lends little support to these gloomy headlines. 

It is interesting to note that in a different study of congenital birth defects in Iraqi cities the I7-foId increase in Basra hospitals is attributed to lead (Al-Sabbak et al. 2012). 

A study on the effects of repeated inhalation of UO2 by rats was conducted and the main finding was that the predictions of the biokinetic model were consistent with the results of these experiments (Monleau et al. 2006). Exposure to uranium 

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Domingo JL, Patemain JL, Llobet JM, et al The developmental toxicity of uranium in mice. Arch Environ Health 44 395-398, 1989... 

Wrenn ME, Durbin PW, Willis DL, et al. 1987. The potential toxicity of uranium in water. J AWWA (April) 177-181. 

Fukuda, S., lida, H., Ikeda, M., Yan, X., Xie, Y. (2005). Toxicity of uranium and the removal effects of CBMIDA and EHBP in simulated wounds of rats. Health Phys. 89 81-8. 

Ortega, A., Domingo, J.L., Llohet, J.M., Tomas, J.M., Patemain, J.L. (1989b). Evaluation of the oral toxicity of uranium in a 4-week drinking-water study in rats. Bull. Environ. Contam. Toxicol. 42 935-41. 

The pulmonary toxicity of uranium compounds varies in animals. Reports of pulmonary toxicity in animals after acute-duration exposure to uranium are limited to experiments with uranium hexafluoride. Gasping and severe irritation to the nasal passages were reported after 10 minute exposures at 637 mg U/mg in rats and mice (Spiegl 1949) and nasal hemorrhage in rats after a 5 minute exposure to 54,503 mg/m (Leach et al. 1984). Uranium hexafluoride promptly hydrolyzes on contact with water to uranyl fluoride and hydrofluoric acid. Thus, the animals were potentially exposed to hydrofluoric acid, a potent toxicant to respiratory tract epithelium, which probably contributed to pulmonary tissue destruction (Leach et al. 1984 Spiegl 1949 Stokinger et al. 1953). In addition, exposure to fluoride ions can result in hypocalcemia, hypomagnesemia, pulmonary edema, metabolic acidosis, ventricular arrhythmia, and death (Meditext 1998). 

No information was located regarding the toxicity of uranium to genetic material in humans or animals following inhalation exposures for any duration. 

The chemical action of all isotopes and isotopic mixtures of uranium are identical, regardless of the specific activity, because chemical action depends only on chemical properties. Thus, the chemical toxicities of natural, depleted, and enriched uranium are identical. Current evidence from animals studies suggests that the toxicity of uranium is mainly due to its chemical damage to kidney tubular cells, leading to nephritis. 

Evidence also suggests that the toxicity of uranium varies according to the route of exposure and to its compounds. This finding may be partly attributable to the relatively low gastrointestinal absorption of uranium compounds. Only <0.1-6% of even the more soluble uranium compounds are absorbed in the gastrointestinal tract. On the basis of the toxicity of different uranium salts in animals, it was concluded that the relatively more water-soluble salts (uranyl nitrate hexahydrate, uranyl fluoride, uranium pentachloride) were primarily renal and systemic toxicants. The less water-soluble compounds (uranium trioxide, sodium diuranate, ammonium diuranate) were of moderate-to-low toxicity, while the insoluble compounds (uranium tetrafluoride, uranium dioxide, uranium peroxide, triuranium octaoxide) were... 

No information was located regarding the modulation of the toxicity of uranium by other chemicals or vice versa. It is possible that co-exposure to other heavy metal nephrotoxicants (e.g., lead, cadmium) could have an additive effect on uranium toxicity. 

A number of studies currently being conducted on the toxicity of uranium were found in the Federal Research in Progress database (FEDRIP 1999). Selected studies are listed in Table 2-11. 

Uranium is unusual among the elements because it presents both chemical and radiological hazards. For soluble uranium, with an U enrichment no greater than 5%, limits on intakes and air concentrations for radiation workers are based on the chemical toxicity of uranium since it is more limiting than the radiological hazard. For this case, the USNRC s limit for a 40-hour workweek is 0.2 mg uranium per cubic meter of air average (USNRC 1993f). 

Domingo JL, Llobet JM, Tomas JM, et al. 1987. Acute toxicity of uranium in rats and mice. Bull... 

Maynard EA, Down WL, Hodge HC. 1953. Oral toxicity of uranium compounds. In Voegtlin C, Hodge HC, eds. Pharmacology and toxicology of uranium compounds. New York, NY McGraw-Hill. 

Stopps GJ, Todd M. 1982. The chemical toxicity of uranium with special reference to effects on the kidney and the use of urine for biological monitoring. Prepared for the Atomic Energy Control Board, Ottawa, Canada. CA 8306480. NTIS DE 84-701123. 

Tishkoff, G. H., Pharmocology and Toxicity of Uranium Gompounds, Part 1, Chapter 1, Appendix B, McGraw-Hill, New York, 1949. 

In contrast, the chemical toxicity of uranium is more important than its radiological hazard. In body fluids, uranium is present as soluble U(VI) species and is rapidly eliminated from the body (60% within 24 h Goyer and Clarkson (2001)). It is rapidly absorbed from the gastrointestinal tract and moves quickly through the body. The uranyl carbonate complex in plasma is filtered out by the kidney glomerulus, the bicarbonate is reabsorbed by the proximule tubules, and the liberated uranyl ion is concentrated in the tubular cells. This produces systemic toxicity in the form of acute renal damage and renal failure. 

Tuovinen, O.H. and Kelly, D.P., (1974 (a) (b) (c). Studies on the growth of Thiobacillus ferrooxidans. II. Toxicity of uranium to growing cultures and tolerance conferred by mutation, other metal cations and EDTA. Arch. Mikrobiol., 95 153—164. III. Influence of uranium, other metal ions and 2,4-dinitrophenol on ferrous iron oxidation and carbon dioxide fixation by cell suspensions, ibid, 95 165—180. IV. Influence of monovalent metal cations on ferrous iron oxidation and uranium toxicity in growing cultures, ibid, 98 167—174. 

The chemical toxicity of uranium compounds is well known when compared to the toxicity of most other compounds. In 1824, a treatise described uranium salts as feeble poisons when given by mouth to animals. In the late 1800s, uranium salts were used as homeopathic therapeutic agents in humans, primarily for treatment of diabetes. In the early 1900s, the renal toxicity of uranium became apparent in humans, and its use as a therapeutic agent ceased. 

Leggett RW (1989) The behavior and chemical toxicity of uranium in the kidney a reassessment Health Phys 57 365-383... 

Domingo JL (1995) Chemical toxicity of uranium. Toxicol Ecotoxicol News 2 74-78 Pellmar TC, FudareUi AF, Ejnik JW, Hamilton M, Hogan JB, Strocko S, Emond C, Laundauer M (1999) Toxicological evaluation of depleted uranium in rats implanted with depleted uranium pellets. Toxicol Sci 49 29-39... 

This chapter deals with several aspects of the effects of uranium on human health. It begins with a description of the pathways through which humans may be exposed to uranium compounds, continues with a discussion of the toxicity of uranium, and concludes with a survey of the techniques used for determining exposure and assessment of dose incurred. As this treatise is concerned mainly with the analytical chemistry of uranium, each of these topics includes some representative examples of the analytical techniques and sample preparation procedures used. As will be shown later, there are many types of analytical instruments, measurement methodologies, and techniques, and there is no approach that is universally accepted as the definitive method. As always, the analyst should consider the available instrumentation, the information required, and the preparation method best suited for the specific type of sample. The main points in each section are summarized in the form of highlights just like in the other chapters. 

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