Uranium in blood

Chevari, S., Likhner, D. (1968). Complex formation of natural uranium in blood. Med. Radiol. (Mask.) 13 53-7. 

In animals, a substantial fraction of plasma uranium is associated with the ultrafilterable low-molecular-weight fraction, and the remainder is weakly associated with transferrin and other plasma proteins. Data on baboons indicate that 50% or more of the uranium in blood is associated with the red blood cells during the period 10-1,000 hours after injection. These data have been interpreted to mean that about 0.7% of the uranium leaving the plasma attaches to red blood cells and is returned to plasma with a halftime slightly greater than 1 day (ICRP 1995). 

Six tissues and blood represent the most important sites for intake, metabolism, and deposition in humans. They are important because (1) some inhaled uranium deposits in the lung and is transferred to blood, (2) uranium in blood is transferred via bile to the liver, (3) uranium is excreted through the kidney, a target organ for heavy metal deposition, (4) muscle and (5) fat represent 60% of the total reference body weight, (6) skeleton or bone accumulates calcium analogs and is... 

Highlights Analytical procedures for bioassays of uranium in blood and feces have been developed and used in a limited number of studies. Compared to urinalysis, the collection and handling of blood and feces are complicated and entail special procedures. The preparation of fecal samples involves dry-ashing at an elevated temperature and then acid digestion. For alpha spectrometry, separation, purification, and deposition precede counting (that could last several days per sample). Other analytical techniques described in the literature include neutron activation analysis, but ICPMS is currently more widely used. 

Chaudhri, M.A. and Watling, R.J. (2010). Measurement of uranium in blood-plasma of Bavarian females. In 10th Radiation Physics and Protection Conference (pp. 111-113), Nasr City, Egypt. 

Lucas, H.F. and Markun, F. (1970). Thorium and uranium in blood, urine and cigarettes. Argonne National Laboratory Radiation Physics Division annual report. Part 2 (pp. 47-52), ANL-7760. Argoime, IL Argonne National Laboratory. 

Othman, I. (1993). The relationship between uranium in blood and the number of working years in the Syrian phosphate mines, J. Environ. Radioact. 18, 151-161. 

Deng Zhi-cheng and Li Yuan-huy, The Main Cause of Chromosome Aberration Increase in Blood Lymphocytes of Uranium Miners, Private Communication from Department of Radiation Medicine, North China, Institute of Radiation Protection China (1983) ... 

Once absorbed into the system circulation, uranium undergoes chemical transformations to complex with the blood. Uranium in the trivalent form will oxidize to the hexavalent species to form uranyl ions, which form soluble complexes with bicarbonate, citrate, or proteins in the plasma (Chevari and Likhner, 1968 Cooper et al, 1982 Stevens et al, 1980). The distribution of uranium in the blood is approximately 47% complexed with bicarbonate in plasma, 32% bound to plasma proteins, and 20% bound to erythrocytes (Chevari and Likhner, 1968, 1969). 

The concentrations of uranium in human blood from New York City donors averaged 0.14 mg U/kg in both whole blood and red cells, compared to values ranging from <0.04 to 86 mg U/kg globally (Fiseime and Perry 1985). The median concentrations of uranium in the lungs, liver, kidneys, and vertebra from... 

Intravenously injected uranium is rapidly taken up by the tissues or excreted in the urine (ICRP 1995). Typically, 25% of intravenously injected uranium (as uranyl nitrate) remained in blood of human subjects after 5 minutes, 5% after 5 hours, 1% after 20 hours, and less than 0.5% after 100 hours although inter-subject variation was high (Bassett et al. 1948 Bernard and Struxness 1957). Measurements of systemic distribution of uranium made at autopsy in one terminally ill human given a single intravenous injection of uranium indicated that the skeleton, kidneys, and other soft tissues after 2.5 hours contained about 10, 14, and 6%, respectively, of the dose. Distribution data taken from another human subject 18 hours after a single intravenous injection uranium showed that the bones, kidneys, and other soft tissues contained about 4-13%, 6%, and 4%, respectively, of the amount injected. At 566 days post-injection, uranium distribution in the skeleton, kidneys, and other soft tissues declined to about 1.4, 0.3, and 0.3%, respectively. 

Uranium is usually found in compounds which can be metabolized and recomplexed to form other compounds. In body fluids, tetravalent uranium is likely to oxidize to the hexavalent form followed by formation of uranyl ion. Uranium generally complexes with citrate, bicarbonates, or protein in plasma (Cooper et al. 1982 Bounce and Flagg 1949 Stevens et al. 1980). The stability of the carbonate complex depends on the pH of the solution, which will differ in different parts of the body (BEIRIV 1988). The low-molecular-weight bicarbonate complex can be filtered at the renal glomerulus, and be excreted in urine at levels dependent on the pH of the urine. The uranium bound to the protein (primarily transferrin) is less easily filtered and is more likely to remain in blood. In the blood, the uranyl ion binds to circulating transferrin, and to proteins and phospholipids in the proximal tubule (Wedeen 1992). 

Transfer of uranium across the placenta was investigated in an animal study, but no information is available for humans. In the animal study, only 0.01-0.03% of an intravenous dose of uranium to rat dams crossed the placenta (Sikov and Mahlum 1968) thus if an inhalation, oral, or dermal exposure was sufficient to raise the blood uranium level, a very limited amount of uranium might cross the placenta. No studies were located regarding uranium in breast milk. Based on the chemical properties of uranium, it seems unlikely that there would be preferential distribution from the blood to this high-fat compartment. It is not known if uranium has any effect on the active transport of calcium into breast milk. Most of the adult body burden of uranium is stored in bone (ICRP 1979, 1995, 1996). It is not known if maternal bone stores of uranium (like those of calcium and lead) are mobilized during pregnancy and lactation. 

More information is needed on the absorption of various forms of uranium in young animals. Also, studies are needed on whether maternally stored bone uranium is mobilized to blood during pregnancy and lactation and whether this can increase exposure to the fetus and neonate. Child health data needs relating to exposure are discussed in Section 5.8.1, Data Needs Exposures of Children. 

The excretion of uranium in fecal material results primarily from intakes by ingeshon, and includes uranium swallowed after inhalation. Usually, uranium will appear in feces within hours after intake thus providing a rapid means of determining whether an intake has occurred. Fecal analysis requires prechemistry preparation that includes ashing of the sample, cleaning by co-precipitation, and solvent extraction followed by electrodeposition. Alpha spectroscopy is then performed (Singh and Wrenn 1988). Urinalysis is typically favored over both fecal and blood analysis because it is generally more sensitive and less costly, and because fecal analysis provides no uptake or retention information and blood analyses is invasive. 

About 99 percent of the uranium ingested in food or water will leave a person s body in the feces, and the remainder will enter the blood. Most of this absorbed uranium will be removed by the kidneys and excreted in the urine within a few days. A small amount of the uranium in the bloodstream will deposit in a person s bones, where it will remain for years. 

Wagner V, Andriikova J, Sevc J. 1973. Investigation of immunoglobulin levels in blood-serum of uranium miners after a higher exposure to ionizing radiation. In Bujdoso E (ed). Health physics problems of internal contamination. Budapest Akademiai Kaido, 341-347. 

The negative intercept indicated that the urinary excretion from a dietary source was not evident and that some retention may have occurred. The slope of the line indicated that about 5% of the uranium in water was absorbed into blood and excreted in urine. The authors concluded that for steady-state ingestion of uranium water is the primary pathway for absorption and not total dietary intake under normal chronic conditions. 

The distribution of uranium in the human body, based on the mean concentrations in Table 4, the mean bone concentration given above, and the ICRP Reference Man tissue and blood weights, is depicted in Fig. 1. Clearly the skeleton is the primary repository of uranium in humans, but because of the large masses of fat and muscle, these tissues may approach the quantity in bone. Confirmatory measurements of uranium in muscle and fat should be made since the estimates are based on only one and two reports, respectively. The total body content based on global estimates of these soft tissues, blood, and bone is 55 p.g of uranium (680 mBq). The ICRP estimated the uranium content of Reference Man to be 90 p.g (1100 mBq) [27]. The primary difference in these estimates is the evaluation of the skeletal content. 

TABLE 4. Concentrations of Uranium in Soft Tissues and Blood... 

FIG. 1. Distribution of uranium in human tissues and blood given as the number of (ng of U in the human body. 

In Chapter 4, we discuss the effects of uranium on human life and well-being with a detailed survey of the methods and means of estimating internal exposure to uranium on the basis of bioassays (urine, feces, blood, hair, nails, and some nonstandard assays). We also present a detailed review of the analytical methods used to assess the amount of uranium in food products and drinking water that are the main pathways of exposure to uranium of the general population. 

Uranyl carbonate complexes, like sodium uranyl tricarbonate, Na4[U02(C03>3], that is obtained when uranium ore is leached with sodium carbonate solutions and ammonium uranyl carbonate (AUC), (NH4)4[U02(C03)3l, that is used to precipitate the uranium in the UCF, are important in the NFC. These carbonates serve to purify the uranium from several metals (like Fe, Al, Cr, Ni, and other metals) that are precipitated as hydroxides or oxycarbonates, as well as aUcaline-earth elements. These purification methods utilize the effect of the ammonium carbonate concentration on the solubility of uranium. Upon heating of AUC to 300°C-500°C, it decomposes to UO3, ammonia, CO2, and water and at temperatures of 700°C-800°C, without air, UO2 may be formed (the ammonia serves as the reducing agent). The solubility of AUC decreases markedly in the presence of ammonium carbonate, for example, from 119.3 g L" at 50°C without ammonium carbonate to 0.5 g L" with 35% ammonium carbonate (Galkin 1966). The carbonate complexes also play a role in biological systems and affect clearance by the blood after exposure to uranium compounds. 

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