Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “THORIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed2001

Strong ligands for thorium complexation in marine bacteria.

The interaction between thorium and marine organisms (cultured heterotrophic bacteria) was experimentally examined by using chemical equilibrium techniques. Thorium (Th) quantitatively reacts with a binding site on bacteria (Alteromonas, Vibrio, Pseudomonas and Flavobacterium) in 0.1 M HCl solution. According to mass balance analysis of adsorption experiment data, Th forms a 1:1 complex with a binding site similar in reactivity among bacteria used in this study, whose conditional stability constants are in the range from 10(6.63) to 10(7.07) M-1 under the experimental conditions of a 0.1 M HCl solution. The mole ratio of the strong ligand to organic carbon in bacteria ranged from 2.3 to 4.3 mmol/mol C. The strong ligand/carbon ratios in bacteria were more than one order of magnitude greater than in phytoplankton, zooplankton or other organic ligands in surface waters. The results suggest that the strong organic ligand reacting with Th is one of the functional groups commonly existing in oceanic microorganisms. The conditional stability constants of the Th complexes with the binding site in marine microorganisms are in the same order of magnitude as that with the strong ligand found in particulate and dissolved organic matter. These findings strongly suggest that the strong ligand in particulate and dissolved organic matter, reacting with trace metals under the conditions of seawater, originates from marine organisms.

Bacteria↗
PubMedDate not supplied

Exposures from thorium contained in thoriated tungsten welding electrodes.

Information provided in this article can be used for estimating the radiation dose associated with the use of thoriated tungsten electrodes in tungsten inert gas welding. Area and breathing zone concentrations of 232Th generated by welding and electrode sharpening along with particle size information; isotopic composition of electrodes from two domestic manufacturers and one European manufacturer; and process variables and estimates on the number of thoriated tungsten electrodes manufactured are presented. Past literature is reviewed and compared with the results of this study. Isotopic analysis of a nominal 2% thoriated electrode found 0.6 ppm +/- 0.4 ppm 230Th and less than 0.1 ppm 228Th. Analysis of a ceriated tungsten electrode and a lanthanated tungsten electrode for 232Th found 124 ppm and 177 ppm, respectively. Electrode consumption during welding was primarily the result of tip sharpening. Less than 3% of the weight loss was attributable to the welding process. The in-mask concentration of respirable thorium particulate in the welder's breathing zone was 0.002 x 10(-12) microCi 232Th/mL. The concentration of respirable thorium particulate from electrode sharpening was 1.3 x 10(-12) microCi 232Th/mL. The measured sharpening time was 20 sec per electrode. Estimates of the activity median aerodynamic diameters for the respirable fraction of the welding and electrode sharpening aerosols were 3.5 and 5 microns, respectively, when measured in the breathing zone at 0.3 m (12 inches) from the point of operation. The respirable fraction of the total welding and sharpening aerosols was 45 and 60%.

Air Pollutants, Occupational↗
PubMed2005

Recent results from a study of thorium lung burdens and health effects among miners in China.

The purpose of this study was to obtain more information about health effects among the dust-exposed male miners of Bayun Obo Rare-Earth and Iron Mine, China. From 2,390 male miners from the seven dust-generating workshops of the mine, 136 dust-exposed miners were randomly selected for study. Of these, 64 men were from the high-dust-generating workshop and 72 from the lower-dust-generating workshops; the latter group was used as an internal control. Physical measurements and medical examinations were carried out on each of these 136 men. The average measured thorium lung burden for the high-dust-exposure miners was significantly greater than that for the group of lower-exposure miners, and the incidence of severe breathlessness and pneumoconiosis of stage 0(+) was also significantly raised in the high-exposure group relative to the low-exposure group. An epidemiological study of lung cancer mortality among all the miners and staff of this mine was also carried out. This showed significantly raised levels of lung cancer mortality in both exposed miners and unexposed workers when compared with the Chinese population, and the level in exposed miners was significantly higher than that in unexposed men. The general high rate of lung cancer mortality in the workers of the mine is attributed to high levels of cigarette smoking, and the raised rate in the exposed miners relative to the unexposed workers to inhalation of silica- and thorium-bearing dusts and thoron progeny.

Adult↗
PubMed2001

Experiences in the determination of activity in thorium contaminated materials in working areas, using gamma spectrometer measurements, from the viewpoint of practical radiation protection.

In industrial processes, classification and clearance of thorium contaminated material is often a time problem. Short-term decisions have to be made about acceptance limits, industrial safety as the workers are in contact with the contaminated material. and the environmental aspect regarding the disposal of the wastes. The use of gamma ray spectrometry measurements is an easy method to estimate the level of activity in materials. Under the precondition of equilibrium of activity within the thorium decay chain, which can be assumed only with knowledge of the materials' history, adequate results can be produced in a reasonable time. The advantages of gamma ray spectrometry are the low investment and operational costs, simple sample preparation, and a system that is relatively quick and easy to operate.

Humans↗
PubMed2001

Thorium isotopic analysis by alpha spectrometry.

The technique of alpha spectrometry is used to detect alpha particles and to determine their energy. In this way the technique is able to provide simultaneously quantitative information (i.e. the activity) and qualitative information (the identity) on any radionuclide that emits an alpha particle. The longer-lived naturally occurring isotopes of thorium are all alpha emitters so the technique can be used to quantify them directly and this is extremely important if radiation doses due to intakes of these isotopes into the body are to be accurately assessed. The principle of the technique is discussed, its advantages and disadvantages, and the instrumentation that is commonly used today. The need for radiochemical separation is discussed and illustrated by reference to analysis procedures in current use for thorium isotopic analysis. Practical issues such as detection limits, quality control procedures. sample throughput and cost will be covered.

Alpha Particles↗
PubMed2001

Nuclear data used in the analysis of thorium in the workplace.

The analysis of thorium in the workplace can be achieved using a variety of metrological techniques. The uncertainty on the final measured values will include components that arise from the uncertainties in the nuclear data that are used. These data include half-lives, branching ratios and gamma ray emission probabilities. It is important that a common, consistent and reliable data set is used in order to minimise the potential differences between analytical results. With particular reference to the problems associated with thorium analysis, some of the various sources of nuclear data are discussed and a recommended set of data is proposed.

Databases as Topic↗
PubMed2004

Dosimetric assessment from 212Pb inhalation at a thorium purification plant.

At the Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, Brazil, there is a facility (thorium purification plant) where materials with high thorium concentrations are manipulated. In order to estimate afterwards the lung cancer risk for the workers, the thoron daughter (212Pb) levels were assessed and the committed effective and lung committed equivalent doses for workers in place. A total of 28 air filter samples were measured by total alpha counting through the modified Kusnetz method, to determine the 212Pb concentraion. The committed effective dose and lung committed equivalent dose due to 212Pb inhalation were derived from compartmental analysis following the ICRP 66 lung compartmental model, and ICRP 67 lead metabolic model.

Administration, Inhalation↗
PubMed1984

Ambient monitoring of airborne radioactivity near a former thorium processing plant.

Twenty-four hour sampling for airborne radioactivity near a former thorium and rare-earth extraction facility was conducted for approx. 2 months with high-volume and dichotomous air samplers. Thoron ( 220Rn ) daughters were identified in the air and confirmed to be originating from the waste storage site. High-volume samplers near the facility measured average 212Pb concentrations of 177, 43, and 237 pCi/m3 with corresponding ranges of (1.9-1351), (1.5-301) and (0.73-2201)pCi/m3. Simultaneous measurements with dichotomous samplers at the same sites measured average 212Pb concentrations on coarse particulates (2.5-15 microns dia.) of 14, 4 and 10 pCi/m3 and on fine particulates (less than 2.5 microns dia.) of 94, 9 and 214 pCi/m3, respectively. Corresponding ranges were (0.2-109), (0.1-63) and (0.1-94) pCi/m3 for coarse particulates and (0.7-1094), (0.4-101) and (0.5-2685) pCi/m3 for fine particulates. Uranium, thorium and radium radionuclides were not identified as being present in significant concentrations in the particulate samples.

Air Pollutants↗
PubMed1992

Microdistribution and microdosimetry of thorium deposited in the liver.

The distribution of thorium in the liver of a patient 36 y after injection with Thorotrast was examined with autoradiographic and scanning electron microscope backscatter image techniques. Autoradiographic examination of randomly selected histologic sections of the liver showed a total alpha activity calculated at 33.7 Bq g-1, with the highest concentration of alpha activity sequestered in subcapsular scare tissue. Subcapsular scare tissue received 4.8 cGy d-1 of alpha radiation, periportal areas were accumulating 1.4 cGy d-1, and the hepatic cord areas 0.09 cGy d-1 of alpha radiation at the time of death. The concentration of dose in periportal areas correlates with higher incidence of bile duct tumors (than hepatocellular carcinomas) found in patients exposed to Thorotrast. The backscatter technique was demonstrated as useful for identifying thorium in liver specimens.

Aged↗
PubMed1995

Measurements of air concentrations of thorium during grinding and welding operations using thoriated tungsten electrodes.

An evaluation was performed to determine whether thorium was present in concentrations above the derived air concentration during grinding and welding operations using thoriated tungsten electrodes. A few of the advantages of using thoriated tungsten electrodes in industry include easier are starting, greater stability, and reduced weld metal contamination. The electrodes used in this evaluation contained 2% thoria (thorium oxide) and were either 2.4 mm or 3.9 mm in diameter. Personal breathing zone and area air samples were collected for the experienced welders participating in this evaluation during grinding operations. The results during the grinding operations for personal and area air samples were generally below the derived air concentration (DAC) for 232Th for solubility class Y of 0.04 Bq m-3 (1 x 10(-12) microCi mL-1) as per 10 CFR 20. The area samples collected during welding operations were below the DAC.

Air Pollutants, Occupational↗
PubMed1996

Comparison of direct alpha spectrometry and neutron activation analysis of aerosol filters for determination of workplace thorium air concentrations.

Direct alpha spectrometry with three different filter types was investigated for the determination of thorium air concentrations at workplaces in the manufacturing process of discharge lamps containing thoriated tungsten electrodes. The method was compared with neutron activation analysis over an activity range of five orders of magnitude. Within the experimental limits of error, both methods were found to be comparable with respect to sensitivity and accuracy. The advantage of direct alpha spectrometry, however, is that it is less laborious than neutron activation analysis and that it supplies information on the degree of radioactive equilibrium of the thorium series, which is important with regard to the estimation of dose.

Aerosols↗
PubMed1998

Managing metabolic model deficiencies for routine radiation protection purposes at a thorium dioxide facility.

At a metallurgical facility using thorium dioxide feed materials, a number of conventional direct- and indirect-bioassay methods were potentially suitable monitoring methodologies when industry-standard dose assessment methodologies were based upon ICRP recommendations issued in 1959. When the ICRP recommended a different dose assessment methodology in 1977, the intake limits for thorium dropped significantly, and conventional bioassay methods for routine monitoring were rendered ineffective. While determining the technical basis for its air monitoring program, the facility noted that the radioactive materials used as feed to the process were highly insoluble. Therefore, their solubility in simulated lung fluids was determined. The results of this determination indicated that the facility's materials, if inhaled, dissolve in the lung at a half-time that is significantly longer than that contained in international consensus standards for Y-class compounds. They also indicated that the secondary dose limits, if adjusted to eliminate the dose contribution from translocated radionuclides, should be higher, and that a derived air concentration based upon more recent international recommendations is more appropriate for use in the facility's routine monitoring program.

Biological Assay↗
PubMed1986

Ultrastructural localization of Thorotrast (thorium dioxide) in human liver by analytical scanning electron microscope.

The distribution of thorium dioxide (Thorotrast) in the liver from a Thorotrast-administered autopsy case was examined stereographically by analytical scanning electron microscopy. Thorium particles were detected in the macrophages of the portal triad and hepatic sinusoid. These macrophages were irregularly shaped and tended to be aggregated. In the sinusoid, accumulation of the macrophages formed a thrombus-like structure. Furthermore, observed in the sinusoid were free Thorotrast particles that appeared to have been released into the sinusoid as a result of breakdown of the macrophages (Kupffer cells).

Carcinoma, Hepatocellular↗
PubMed2006

Cationic hydrous thorium dioxide colloids--a useful tool for staining negatively charged surface matrices of bacteria for use in energy-filtered transmission electron microscopy.

BACKGROUND: Synthesis of cationic hydrous thorium dioxide colloids (ca. 1.0 to 1.7 nm) has been originally described by Müller 22 and Groot 11 and these have been used by Groot to stain acidic glucosaminoglycans for ultrastructure research of different tissues by conventional transmission electron microscopy. RESULTS: Synthesis of colloidal thorium dioxide has been modified and its use as a suitable stain of acidic mucopolysaccharides and other anionic biopolymers from bacteria, either as whole mount preparations or as preembedment labels, is described. The differences in stain behavior relative to commonly used rutheniumred-lysine and Alcian Blue electron dense acidic stains has been investigated and its use is exemplified for Pseudomonas aeruginosa adjacent cell wall biopolymers. For the first time thorificated biopolymers, i.e. bacterial outer cell wall layers, have been analysed at the ultrastructural level with electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), leading to excellent contrast and signal strength for these extracellular biopolymers. CONCLUSION: Application of cationic hydrous ThO2 colloids for tracing acidic groups of the bacterial surface and/or EPS has been shown to be rather effective by transmission electron microscopy. Because of its high electron density and its good diffusibility it stains and outlines electro-negative charges within these biopolymers. In combination with ESI, based on integrated energy-filtered electron microscopy (EFTEM) Th-densities and thus negative charge densities can be discriminated from other elemental densities, especially in environmental samples, such as biofilms.

Animals↗
PubMed1975

Thorium induced hepatic hemangioendothelioma. Roentgen-angiographic findings in two additional cases with clinical "inform and consent" problems.

1. Two additional cases of presumed, thorium-induced hemangioendothelioma of the liver are reported. 2. The angiographic pattern of large venous lakes conforms closely to the pathologic descriitions of this malignancy. 3. To our knowledge, angiography of the thorotrast (and vinyl chloride) liver, before the clinical evolution of malignancy, has not been recorded and may provide information of prognostic and therapeutic value. 4. Incidental identification of thorium deposits in the tissues of clinically healthy patients creates perplexing "inform and consent" problems. Presumably, these must be solved on an individual basis. 5. Because the use of thorotrast has been discontinued since the early 1950s, all physicians reviewing chest and abdominal roentgenograms should be aware of the characteristic appearance of human thorotrast deposits, especially in the liver, spleen and celiac lymph nodes. 6. The number of living thorotrast "carriers" and previous deaths from thorotrast related malignancy seems highly uncertain at this time.

Autopsy↗
PubMed2003

Thorium-232 exposure during tungsten inert gas arc welding and electrode sharpening.

To assess the exposure of welders to thorium-232 (232Th) during tungsten inert gas arc (TIG) welding, airborne concentrations of 232Th in the breathing zone of the welder and background levels were measured. The radioactive concentrations were 1.11 x 10(-2) Bq/m3 during TIG welding of aluminum (TIG/Al), 1.78 x 10(-4) Bq/m3 during TIG welding of stainless steel (TIG/SS), and 1.93 x 10(-1) Bq/m3 during electrode sharpening, with 5.82 x 10(-5) Bq/m3 background concentration. Although the annual intake of 232Th estimated using these values did not exceed the annual limit intake (ALI, 1.6 x 10(2) Bq), we recommend reducing 232Th exposure by substituting thoriated electrodes with a thorium-free electrodes, setting up local ventilation systems, and by using respiratory protective equipment. It is also necessary to inform workers that thoriated tungsten electrodes contain radioactive material.

Air Pollutants, Occupational↗