Uranium insoluble compounds

Insoluble compounds Soluble compounds Turpentine Uranium (natural)... 

On the basis of these facts, it was speculated that plutonium in its highest oxidation state is similar to uranium (VI) and in a lower state is similar to thorium (IV) and uranium (IV). It was reasoned that if plutonium existed normally as a stable plutonium (IV) ion, it would probably form insoluble compounds or stable complex ions analogous to those of similar ions, and that it would be desirable (as soon as sufficient plutonium became available) to determine the solubilities of such compounds as the fluoride, oxalate, phosphate, iodate, and peroxide. Such data were needed to confirm deductions based on the tracer experiments. 

Toxicology. Uranium is a weakly radioactive alpha-emitting heavy metal that exists in several isotopic forms. Insoluble compounds... 

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for uranium (soluble and insoluble compounds, as U) is 0.2 mg/m with a short-term excursion limit (STEL) of 0.6mg/mk... 

Kurlyandskaya EB. 1970. Certain aspects of the toxicology of insoluble compounds of thorium-232 and uranium-238. In Letavet, Kurlyandskaya, eds. The toxicology of radioactive substances, Vol. 4. New York Pergamon Press, 1-8. 

The stoichiometry of the complexes between HDBP and U(VI) changes with the acidity, that is, at high nitric acidity, the presence of [U02(N03)2(HDBP)TBP] and [U02(N03)2(HDBP)2], and at low nitric acidity, the forms [U02(N03)(DBP)(HDBP)J, [U02(DBP)2(HDBP)J (where x = 1 or 2) dominate. The presence of such complexes can explain the difficulties in U(VI) recovery (114, 115, 120). Otherwise, various authors have indicated the presence of insoluble compounds for enriched uranium solutions (121-124). Recently, Powell identified the solid forms with various spectroscopic methods at lower acid concentrations, the well-characterized polymer U02(DBP)2 precipitates as a yellow powder, whereas a sticky solid or gels are formed at high acidity. The global formula is U02(N03)(H(DBP)2)(HDBP)2 (106). 

Electron microscopy and X-ray microanalytical methods showed that uranium as uranyl nitrate hexahydrate penetrated the stratum corneum within 15 minutes and accumulated in the intracellular space between the viable epidermis and the stratum corneum (De Rey et al. 1983). As is the case with inhalation and oral absorption, water solubility is an important determinant of absorption, and no penetration was observed with the insoluble compounds uranium dioxide, uranyl acetate, or ammonium diuranate. After 48 hours, uranium applied as uranyl nitrate was no longer found in the skin and toxicity developed, indicating that the uranium had been absorbed into the blood. 

In animals, uranium that has been absorbed from the lungs leaves the blood very quickly for distribution to body tissues. The insoluble compounds (uranium tetrafluoride, uranium dioxide) were found to accumulate in the lungs and lymph nodes with the amount retained dependent on the exposure concentration and duration. In a continuous exposure study, more than 90% of the uranium retained at the end of the first year of exposure to a uranium dioxide aerosol was cleared by the end of the second year despite continued inhalation of uranyl nitrate. All of the uranium retained following one year of inhalation of uranyl hexafluoride was cleared by the end of the second year. For uranyl nitrate inhalation, no retention was found in the soft tissues. Uranium has also been shown to accumulate in the tracheobronchial lymph nodes, lungs, bones, and kidneys of rats, dogs, and monkeys exposed to uranium... 

One site of deposition for the soluble compounds (uranyl nitrate, uranium tetrachloride, uranium hexafluoride) in animals was the skeleton, but accumulation was not seen in bone at levels below 0.25 mg U/m over a period of 2 years in rats exposed to soluble compounds (uranyl nitrate, uranium tetrachloride, uranium hexafluoride) in one study. The insoluble compounds (uranium hexafluoride, uranium dioxide) were found to accumulate in the lungs and lymph nodes after the inhalation exposure. For uranyl nitrate exposure, no retention was found in the soft tissues. Accumulation of uranium was also found in the skeleton (Stokinger 1953). The amount distributed in the skeleton has been reported to be 23 5% of the intake in dogs (Morrow et al. 1972) 28-78% in rats (Leach et al. 1984) and 34-43% in guinea pigs (Leach et al. 1984). A biological half-time of 150-200 days (Ballou et al. 1986) or 70 days (Morrow et al. 1982) in the skeleton has been reported following inhalation exposure to soluble uranium compounds (e.g., uranium hexafluoride). 

The insoluble compounds of uranium accumulated to a lesser extent in tissues. Only small amounts of uranium were found in the kidneys (3-9 pg/pair of kidneys) of female mice that were exposed orally to uranium tetrafluoride at 4,437 mg U/kg/day for 48 weeks. No uranium was found in the bone (Tannenbaum and Silverstone 1951). Only small amounts of uranium were found in kidney (1-3 pg/pair of kidneys) of female mice that were exposed orally to triuranium octaoxide at 1,655 mg U/kg/day for 48 weeks. No uranium was found in the bone (Tannenbaum and Silverstone 1951). 

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). 

The main site of long-term retention for soluble uranium compounds (uranyl nitrate, uranium tetrachloride, uranium dioxide) is the bone, while the inhaled insoluble compounds (uranium... 

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... 

The effects of uranium in animal experiments were also compound-dependent, the more water-soluble compounds (e.g., uranyl nitrate) causing much greater renal toxicity than insoluble compounds (e.g., uranium dioxide) when the dose contained equivalent amounts of uranium. ATSDR has determined that the toxicity database for uranium justifies the derivation of separate MRLs for soluble and insoluble forms of uranium for certain durations and routes of exposure. This is based on toxicokinetic evidence that absorption of uranium (and concentration in target tissue) is significantly greater during exposure to the more water-soluble compounds. Soluble forms include uranyl fluoride, uranium tetrachloride and uranyl nitrate hexahydrate insoluble forms include uranium tetrafluoride, uranium dioxide, uranium trioxide, and triuranium octaoxide. Where the database is not extensive enough to allow separate MRLs, the MRL for the soluble form should be protective for health effects due to all forms of uranium. 

An MRL of 8x10 mg U/m has been derived for intermediate-duration inhalation exposure (15-364 days) to insoluble compounds of uranium. 

ATSDR has derived an MRL of 8.0x10 mg U/m for intermediate-duration inhalation exposure to insoluble compounds of uranium based on a NO ART, of 1.1 mg U/m for renal effects in dogs (Rothstein 1949b). 

The fiuorosulfate dihydrate, PaF2S04 2H2O, analogous to the known uranium(IV) compound (1S2), is precipitated on the addition of aqueous hydrofluoric acid to solutions of protactinium(IV) in dilute sulfuric acid (131). Others (71, 84) have reported the formation of a white, insoluble precipitate in hydrofluoric acid, believed to be a tetrafluoride hydrate, but the product has not been completely characterized. 

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