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The ultrastructual localization of thorium dioxide was examined in liver biopsy specimens from two patients injected more than 30 years before with thorotrast. An energy dispersive X-ray microanalysis spectrometer (Kevex 5100) was used to identify thorium in the liver tissue. By electron microscopy, most of the thorium particles were found in the cells of the reticuloendothelial system, such as macrophages of the portal triad and Kupffer cells in the hepatic sinusoid. Thorium dioxide particles were mainly located within the phagosomes, but larger aggregates existed in the cytoplasma with no visible limiting membrane. In addition, the deposition of thorium granules in a few hepatocytes was also confirmed by electron microscopy. This fact indicates that two main pathways of elimination are still functioning in the late period, but the hepatocytic pathway appears to be less effective than the reticuloendothelial system.
The use of thoriated tungsten electrodes may be at the origin of a potential hazard for the personnel involved in the use of electrodes, as well as the general population. To assess this hazard, the electrode radioactivity measurements by alpha and beta counting has been conducted. The radioelements were identified by alpha and gamma spectromety. It appeared that there was a radioactive disequilibrium between thorium-232 (Th-232) and it daughters atoms. Additionally, some thorium 230 (Th-230) belonging to the uranium chain, was present. The chemical separation and the milling processing had affected the radioactive composition and the thorium in the electrodes, doesn't exactly corresponds to natural thorium. Radiation doses were also assessed: film and photoluminescence dosimetry were undertaken. Finally smears method showed a alpha removable area contamination. Even if the hazard is weak. As a matter of fact, it must not be neglected because it was complex, for the thorium was always accompanied by Th-232 progeny, alpha emitters but also beta and gamma emitters.
Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides have been studied for 2 phosphate rocks and 7 phosphate fertilizers. Uranium contents were found to be rather high (39-117 ppm) except for phosphate rock from Kola. The uranium series nuclides were found to be in various equilibration states, which can be grouped into following three categories. Almost in the equilibrium state, 238U approximately 230Th greater than 210Pb greater than 226Ra and 238U greater than 230Th greater than 210Pb greater than 226Ra. Thorium contents were found to be, in general, low and appreciable disequilibrium of the thorium series nuclides was not observed except one sample. Potassium contents were also very low (less than 0.3% K2O) except for complex fertilizers. Based on the present data, discussions were made for the radiation exposure due to phosphate fertilizers.
X-ray absorption fine structure (XAFS) spectroscopy at the Th L3 edge is applied for the characterization of crystalline, anhydrous ThO(2)(cr), microcrystalline ThO(2).xH(2)O(s), amorphous ThO(n)(OH)(4-2n).xH(2)O(am), aqueous Th(IV) solutions, and colloidal suspensions up to p(c)H 3.7. The microcrystalline, possibly hydrated thorium dioxide, is formed at p(c)H 1.5-2.5 by precipitation from suspensions of 16-23 nm thorium dioxide colloids. The solubility data determined for this solid is several orders of magnitude lower than the values for amorphous Th(IV) hydroxide or hydrous oxide. The EXAFS spectrum of the isolated microcrystalline particles shows that their structure is different from that of anhydrous crystalline ThO(2)(cr) and amorphous ThO(n)(OH)(4-2n).xH(2)O(am) precipitated at higher pH and dried at room temperature. The solubility measured for the amorphous Th(IV) precipitate is comparable to that previously reported for a solid prepared in a similar manner. In other solubility studies with amorphous Th(IV) hydroxide or hydrous oxide, considerably higher thorium concentrations are measured at p(c)H 3.5-5. The aqueous speciation is made by EXAFS for solutions prepared by careful coulometric titration under comparable conditions (p(c)H and thorium concentration). The spectra of these solutions demonstrate the presence of a large amount of Th(IV) polynuclear species or colloids of small size, having a highly asymmetric Th-O coordination. The EXAFS spectrum of these colloids is similar to that of the amorphous solid.
Higher than environmental levels of (232)Th have been found in autopsy samples of lungs and other organs from four former employees of a thorium refinery. Working periods of the subjects ranged from 3 to 24 years, and times from end of work to death ranged from 6 to 31 years. Examination of the distribution of thorium among the organs showed that concentrations in the lung relative to pulmonary lymph nodes, bone or liver were much higher calculated from the dosimetric models in Publication 30 of the International Commission on Radiological Protection (ICRP). Much better agreement was found with more recently proposed models in Publications 68 and 69 of the ICRP. Radiation doses estimated from the amounts of thorium in the autopsy samples were compatible with health studies that found no significant difference in mortality from that of the general population of men in the U.S.
Concentrations of 232Th and activity ratios of 228Th to 232Th and 230Th to 232Th were determined in autopsy samples from five former employees of a thorium refinery. The ranges of 232Th activity concentrations (mBq per gram of wet tissue) were 0.17-94 in lungs, 3.9-1210 in pulmonary lymph nodes, 0.14-1.19 in bones, 0.015-0.68 in liver, 0.97-5.8 in spleen, and 0.009-0.068 in kidneys. These concentrations are 10 to 1,000 times greater than have been reported for persons not occupationally exposed to thorium. In most of the samples, the ratios of 228Th to 232Th and 230Th to 232Th activity at death of the subject were 0.2-0.4 and 0.1-0.2, respectively. 228Th to 228Ra activity ratios (+/- standard errors) of 0.86 +/- 0.11 in lungs and 1.18 +/- 0.13 in lymph nodes of one subject were obtained by calculation from ratios of 228Th to 232Th.
A selective and sensitive spectrophotometric method for the determination of Th(IV) has been based on the reaction with thorin and subsequent extraction of the red-orange coloured complex with N-hydroxy-N,N'-diphenylbenzamidine (HDPBA) in benzene as floated complex at pH 2.2. The complex in ethanol exhibits a maximum absorbance at 495 nm, with a molar absorptivity of 6.0x10(4) l mol(-1) cm(-1), with a Sandell's sensitivity of 3.9x10(-3) microg cm(-2). The method follows Beer's law up to 3.0 microg Th(IV) ml(-1). None of the common cations and anions tested interfere. The detection limit of the method is 0.04 microg Th(IV) ml(-1), the RSD (n=10) is 1.4%. The method has been successfully employed for the determination of thorium in various standard and monazite samples.
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