Radiological toxicity

Due to the low speeific radioactivity of natural uranium (about 1 Ci per 3 metric tons or 81 ng U-238 per Bq Frame 4.3), the main health effects are through its chemical toxicity. However, in some cases, the radiological effects may be dominant, like in the case of exposure to enriched uranium or when insoluble uranium compounds enter the body through inhalation or injury and are retained in the body for an extended period. The fact that the decay products of uranium (progeny) are also radioactive may enhance the radiological health effects. 

In that case, the local damage to the cellular material close to the embedded eompound could be severe. In addition, the effects could be delayed and affect the genetic material (teratogenic effect) so will only be expressed in the offspring of the exposed person, as claimed for populations living in zones where DU munitions were used (like Iraq). 

A special case of radiological effects of uranium is when a criticality incident occurs. A criticality accident, or an uncontrolled nuclear chain reaction, may inadvertently occur if a sufficient amount of accumulates under certain conditions. The criteria for criticality control are known by the acronym MAGIC MF.RV for Mass, Absorption, Geometry, Interaction, Concentration, Moderation, Enrichment, Reflection, and Volume (for more details, see Frame 1.3 in Chapter 1). The result would be the emission of neutrons and ganuna radiation, as occurred in Tokai-Mura, Japan, in 1999, and resulted in the death of two of the plant employees (WNA 2007). A brief discussion on the units for measuring radiation and exposure of the public is presented in Frame 4.3. 

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Following intravenous injection of Thorotrast, cirrhosis of the liver was the primary systemic effect in humans and animals. Hematological disorders (aplastic anemia, leukemia, myelofibrosis, and splenic cirrhosis), cardiovascular effects (myocardial infarction, severe coronary luminal narrowing and internal alteration of the carotid artery), and Thorotrastoma (localized fibrosis surrounding deposits of Thorotrast) were also found in patients injected with Thorotrast. The effects of Thorotrast were a result of the radiological toxicity of thorium. 

Thorium is commonly found in combination with other actinide elements, with organic and inorganic chemicals, and with acids and bases during occupational exposure. The health effects of occupational exposures to thorium on humans, therefore, cannot necessarily be attributed to thorium. The daughter products of thorium have unique properties that also add to the radiological toxicity of thorium. For further information, see the toxicological profiles on uranium, radon, and radium. 

DU has 40% less radioactivity than natural uranium, but may contain trace levels of plutonium, neptunium, americium, technetiiun, and U, which increase the radioactivity by 1% but are insignificant with respect to chemical and radiological toxicity (Force Health Protection Readiness Policy Programs, 2008 Sztajnkrycer and Often, 2004 WHO, 2001). Because of the decreased radioactivity of DU, it is believed that DU is a safer form than natural uranium, while maintaining the same chemical properties. As the heaviest occurring element, uranium is extremely dense and both uranium and DU are often used in applications which require such dense metals. 

Brugge, D., de Lemos, J.L., Oldmixon, B. (2005). Exposure pathways and health effects associated with chemical and radiological toxicity of natural uranium a review. Rev. Environ. Health 20 177-93. 

Because natural uranium produces very little radioactivity per mass of uranium, the renal and respiratory effects from exposure of humans and animals to uranium are usually attributed to the chemical properties of uranium. However, in exposures to more radioactive uranium isotopes (e.g., and and naturally occurring and U), it has been suggested that the chemical and radiological toxicity may be additive or may potentiate in some instances. In these instances, this dual mode of uranium toxicity may not be distinguishable by end point because of the overlap of etiology and manifested effects. The mechanism of this interaction is as yet unclear. 

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). 

UNSCEAR has considered that limits for natural (and depleted) uranium in food and drinking water (the most important sources of human exposure) should be based on the chemical toxicity rather than on a hypothetical radiological toxicity, which has not been observed in either humans or animals (UNSCEAR 1993 Wrenn et al. 1985). 

A typical nuclear industry may consist of mining and milling of uranium ore, thorium extraction, fuel fabrication, nuclear reactor operation, and production and application of radioactive isotopes for various industrial medical and research purposes. Almost, in all these steps, waste is generated that needs proper management. Radioactive wastes differ from other industrial wastes due to its radiation exposure and its radiological toxicity to human beings and their environment. Management of radioactive wastes is an important step in a nuclear industry and the objective is to effectively isolate radionuclides from the... 

Some elements nsed in SRDs have chemical as well as radiological toxicity. For example, cesium, an alkali metal, will explode if exposed to water. Cesinm hydroxide, a strong base, is qnite corrosive, and can attack glass. Clinicians and responders will need to be aware of the spectrum of risk posed by chemicals nsed in SRDs and other devices (1). 

The monitoring (cover, drift...), the measures (radiological, toxical, environmental) are done according to programs elaborated following quality assurance criteria. These programs must, at least, specify the reasons for these actions as well as their nature (location, frequency...) and their expected results in normal situations. 

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