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PubMed1998

Radionuclides (lead-210, polonium-210, thorium-230, and -232) and thorium and uranium in water, sediments, and fish from lakes near the city of Elliot Lake, Ontario, Canada.

Radionuclides (210Pb, 210Po, 230Th, and 232Th) and chemical Th and U were measured in water, sediments, and fish tissues (bone, muscle, and gut contents of laketrout, Salvelinus namaycush, whitefish, Coregonus clupeaformis and Prosopium cylindraceum) from four lakes in a watershed affected by U mining and milling operations at Elliot Lake, Ontario, and from control lakes in an adjacent, non-industrialized, watershed. Radionuclide concentration ratios between tissue levels and sediment and water levels were calculated. Annual radionuclide intakes and resulting doses were estimated for humans consuming fish from the watershed. Bone 210Pb levels were higher (186 mBq g(-1) dry wt in laketrout and 230 mBq g(-1) dry wt in one lake whitefish) than in muscle (< 50 mBq g(-1) dry wt in all cases), and generally higher in fish from study lakes than from controls, but no consistent differences were observed among fish species. Similarly, 210Po levels were higher in bone (208 +/- 33 mBq g(-1), in laketrout) than muscle (maximum 26 +/- 4 mBq g(-1), in laketrout), and in study lake populations compared to controls. Laketrout 210Po bone concentrations were higher than previously reported in Canada. Levels of 230Th, 232Th, and Th were below detection limits (20 mBq g(-1), 0.05 microg g(-1)) in body tissues in all fish species. Bone levels of U (14.6 +/- 3.0 microg g(-1), in lake whitefish) were higher than in muscle (most < 0.05 microg g(-1), except 0.12 +/- 0.04 and 0.08 +/- 0.03 microg g(-1) in lake whitefish) in fish from waters affected by industrial activity. In control lakes, bone and muscle levels were lower and not significantly different from each other. Muscle levels did not vary consistently with location. Concentration of 210Pb and U was seen from water and 'gut' material (taken as a surrogate for diet) to bone in laketrout and whitefish, and of U from water to muscle in whitefish, but in no case from sediments to tissues. Human intakes of 210Pb, 210Po, 230Th, 232Th, and U from consuming one meal of fish (375 g) per week could, in aggregate, represent an annual effective dose < 15% of the public dose limit (5 mSv). Monitoring biota living near the decommissioned Elliot Lake U operations, especially of 210Pb levels in fish muscle, with further assessment of human doses attributable to local fish and other animals in the diet, should continue. Because radionuclide effects on fish health (and on other non-human organisms) are of increasing concern, neoplasms, malformations, and reproductive anomalies in local fish deserve examination.

Journal Article↗
PubMedDate not supplied

Mechanisms of thorium migration in a semiarid soil.

Thorium concentrations at Kirtland Air Force Base training sites in Albuquerque, NM, have been previously described; however, the mechanisms of thorium migration were not fully understood. This work describes the processes affecting thorium mobility in this semiarid soil, which has implications for future remedial action. Aqueous extraction and filtration experiments have demonstrated the colloidal nature of thorium in the soil, due in part to the low solubility of thorium oxide. Colloidal material was defined as that removed by a 0.22-microm or smaller filter after being filtered to nominally dissolved size (0.45 microm). Additionally, association of thorium with natural organic matter is suggested by micro- and ultrafiltration methods, and electrokinetic data, which indicate thorium migration as a negatively charged particle or anionic complex with organic matter. Soil fractionation and digestion experiments show a bimodal distribution of thorium in the largest and smallest size fractions, most likely associated with detrital plant material and inorganic oxide particles, respectively. Plant uptake studies suggest this could also be a mode of thorium migration as plants grown in thorium-containing soil had a higher thorium concentration than those in control soils. Soil erosion laboratory experiments with wind and surface water overflow were performed to determine bulk soil material movement as a possible mechanism of mobility. Information from these experiments is being used to determine viable soil stabilization techniques at the site to maintain a usable training facility with minimal environmental impact.

Colloids↗
PubMed2001

Current research activity in the measurement of thorium and the identification of future research needs.

A pre-requisite in the setting and enforcement of regulatory limits for exposure to thorium in the workplace is that thorium and its progeny can be accurately measured. Literature surveys have shown that the majority of thorium measurements were performed using either a radiochemical technique, such as alpha or gamma spectroscopy, or ICP-MS. For many methods. there was a separation step to isolate and pre-concentrate thorium from the sample matrix. Thorium was most commonly measured in geological matrices and industrial materials. A survey of current research activity was performed through distribution of a questionnaire to laboratories and national centres. From the rcsponses, four areas of current activity were identified: (i) development of methods for low level thorium determination, (ii) biological monitoring and metabolism of thorium, (iii) environmental monitoring for thorium, and (iv) health risks from X ray contract media. Two key areas for priority research were identified by the thorium Thematic Network: namely sample preparation methods and for traceable standards and reference materials for thorium analysis.

Environmental Exposure↗
PubMed1988

Microanalytical study of thorium 232 deposits in bone marrow and liver.

Analytical microscopy was used to study the distribution and chemical composition of thorium deposits in bone marrow and liver after injection of thorium dioxide and thorium nitrate. Thorotrast (thorium dioxide) was identified as being localized in bone marrow macrophages of a patient who had undergone cerebral arteriography forty two years ago. Large thorotrast deposits were also present in liver cells. We show that non-colloidal thorium (thorium nitrate) injected in rats concentrates in a non soluble form in bone marrow macrophages, hepatocytes and Kupffer cells. These deposits of thorium associated with phosphorus can be explained by the formation of thorium phosphate in lysosomes and we demonstrate that they remain in tissue for a long time. Microanalysis was performed with ion microscopy, and electron probe microanalysis by X ray spectrometry, which can identify and localize thorium and associated elements at cellular or intracellular level.

Animals↗
PubMed2005

Selective extraction, preconcentration and transport studies of thorium(IV) using octa-functionalized calix[4]resorcinarene-hydroxamic acid.

A new calix[4]resorcinarene bearing eight hydroxamic acid groups (C4RAHA) has been synthesized and characterized by FT-IR, 1H-NMR and elemental analysis. Its analytical properties were investigated, and showed high affinity and selectivity toward thorium(IV) in the presence of large quantities of associated metal ions. Thorium(IV) was extracted from an ethyl acetate solution of C4RAHA at pH 4.5. The lambdamax and molar absorptivity (epsilon) for thorium(IV) were 341 nm and 7120 l mol(-1) cm(-1). The complexation of thorium(IV) with C4RAHA has a 4:1 metal:ligand stoichiometry, which is relatively rare. The extracts were directly aspirated in the plasma for ICP-AES measurements for thorium(IV) in the presence of a diversified matrix. The system obeyed Beer's law over the range 0.1 - 6.5 microg ml(-1) of thorium(IV) with a Sandell sensitivity of 0.0325 microg cm(-2). The preconcentration factor and overall stability constant evaluated at 25 degrees C for thorium(IV) were 133 and 15.86, respectively. The complexation was characterized by a favorable enthalpy change. A liquid-membrane transport study of thorium(IV) was carried out from the source to the receiving phase under controlled conditions, and a mechanism of transport proposed. To check the validity of the proposed method, thorium(IV) was determined in monazite sand, rare earth sand and water samples.

Journal Article↗
PubMed1993

Thorium metabolism and bioassay of mineral sands workers.

The concentration of thorium in the blood serum and urine of Western Australian mineral sands workers was studied to complement estimates of radiation dose derived from air sampling measurements. The concentration of thorium in urine samples from occupationally unexposed persons and pooled serum samples was also investigated. The concentration of thorium in the urine of the workers varied from 3-210 ng L-1 (geometric mean = 31 ng L-1, n = 34) while the concentration of thorium in the serum varied from 170-2,000 ng L-1 (geometric mean = 480 ng L-1, n = 25). No correlation was found between the bioassay results and cumulative airborne thorium exposure. The geometric mean ratio of daily excretion of thorium in urine to total thorium in the serum pool was 2.5%, considerably lower than the value of 10% proposed by the ICRP. These data indicate that more information is required to clarify the biokinetic models for thorium and that doses assessed from air sampling data must be interpreted with caution.

Air Pollutants, Radioactive↗
PubMed2003

Simultaneous spectrophotometric determination of uranium and thorium by flow injection analysis using selective masking.

A flow injection system for the simultaneous determination of uranium and thorium has been developed by using selective masking and a spectrophotometric detector with two flow cells aligned with the same optical path. The injected sample solution was first mixed with a reagent solution containing Chromazurol S (CAS) and cetyltrimethylammonium chloride (CTMAC), and the total absorbance of uranium- and thorium-CAS complexes was measured in the first flow cell at 620 nm. The sample stream was then mixed with an EDTA solution in order to convert the thorium-CAS complex to a thorium-EDTA complex, and the absorbance of the uranium-CAS complex was measured in the second flow cell. The detection limits were 10 microg dm(-3) for uranium and 7 microg dm(-3) for thorium. The calibration graphs were linear (r < 0.9998) at least over the ranges of 0.1 to 10 mg dm(-3) for uranium and 0.08 to 8 mg dm(-3) for thorium. The RSDs were less than 1.5% (n = 3) in the calibration range. Uranium and thorium of up to the 6-fold concentration to each other could be determined in admixtures with relative errors of less than 3.3%. The sample throughput was 24 per hour. The proposed system was successfully applied to the analysis of a uranium-thorium ore mock solution by coupling with anion-exchange in a magnesium nitrate medium to eliminate interference from coexisting elements.

Journal Article↗
PubMed1999

Determination of thorium in organs from thorotrast patients by inductively coupled plasma mass spectroscopy and x-ray fluorescence.

Concentrations of thorium were determined by inductively coupled plasma mass spectroscopy in various organs collected from Japanese Thorotrast autopsy subjects to provide information on dosimetry for Thorotrast patients. Duplicate analyses were performed for 98 samples, and data for thorium in 27 different organs were obtained. The highest thorium level was found in spleen (mean: 16,000 microgram/g wet weight), followed by liver (2100 microgram/g wet weight) and bone marrow (600 microgram/g wet weight). The other concentrations decreased in the following order: lymph node, gallbladder, testis, lung, small intestine, adrenal gland, pancreas, dura, esophagus, muscle, thyroid, large intestine, stomach, fat, kidney, urinary bladder, main artery, prostate, diaphragm, trachea, heart, cerebellum, cerebrum and intervertebral disk. The last four organs showed markedly low concentrations of 2-7 microgram/g wet weight. Compared to the background thorium levels reported in the literature for human organs, the values for the organs from Thorotrast patients (even in the organs with the lowest concentrations) were at least several thousand times higher, suggesting the importance of also considering organs with minor deposition in dosimetry. Distributions of thorium in some selected organs were studied by microbeam X-ray fluorescence. The thorium conglomerates could be identified, and images of microdistributions of thorium in the organ slices were obtained.

Humans↗
PubMed2003

Improved chelation therapy of intramuscularly deposited thorium by CaDTPA in the rat.

Comparative studies on the translocation and retention of intramuscularly (i.m.) injected thorium nitrate (234Th 46 ng + 232Th 5 microg per rat) in solutions of citrate, CaDTPA or citrate + CaDTPA in rats have been conducted. Results showed that only thorium in mixed-ligand solution was entirely translocated from the muscle, with the greatest part being excreted from the body. In this case, the whole-body retention of thorium decreased to 16% of the injected radioactivity within 2 d, 13% being retained in the skeleton. Studies on the decorporation of 234Th + 232Th nitrates from a rat wound simulated with i.m. injection have also been carried out. The greatest translocation of thorium and its excretion was achieved with a single local injection of the mixed-ligand (citrate + CaDTPA) solution when compared with those of citrate or CaDTPA alone. The efficiency of mixed-ligand treatment decreased with its delay. On day 2 post-therapy, the whole-body content of thorium decreased to 30, 37 and 55% of injected radioactivity when the local treatment started immediately, postponed to 1 h or 24 h, after i.m. injection of thorium, respectively. In control rats without treatment, there was only a slight decrease in the content of thorium in the whole body.

Animals↗
PubMed2001

The in vivo assessment of thorium body burden by gamma ray sepctrometry.

Thorium is used in many different industrial technologies and is widely found in nature. Internal contamination with thorium is considered as highly hazardous because of its radiological and chemical toxicities, which depend on the chemical form in which thorium appears. The assessment of the thorium body burden is then of primary importance in detecting the risks of personal contamination, and for appropriate counteractions when contamination is detected. The in vivo assessment of the thorium lung burden is commonly achieved by gamma ray spectrometry of its progeny. Three methods for the assessment of thorium in the lungs are compared. In the first method, the radionuclide examined is 208Tl, measured with a Nal(TI) detector. This simple method can be affected by systematic errors due to 220Rn exhalation and because of the assumption of equilibrium between 232Th and 228Th. The second method, based on the measurement of the gamma rays emitted by 228Ac, requires the use of high-resolution gamma spectrometry (HPGe detectors). The accuracy of the thorium quantification is better with this technique. The third method is based on the measurement of exhaled 220Rn.

Body Burden↗
PubMed1983

Hepatic function in previously exposed thorium refinery workers as compared to normal controls from the health and nutrition survey.

The effect of thorium exposure on hepatic function was investigated in 275 former workers of a thorium refinery. Body burden of radioactivity from the decay chain of thorium was measured as 212Bi and 220Rn in the exhaled breath. Asparate aminotransferase, globulin and total bilirubin in sera were found to be associated with body burden of radioactivity at high levels of significance. Thorium-exposed workers were also compared with a population of white males from the Health and Nutrition Survey conducted by the National Center for Health Statistics from 1971 to 1975. The results showed the means of aspartate aminotransferase alkaline phosphatase to be significantly higher (P = 0.0001) in the thorium-exposed workers when corrected for age, alcohol use and weight. The changes observed in liver function may be compatible with a toxic effect of thorium or daughter products on hepatocytes. The correlation of some hepatic function tests with body burden of radioactivity suggests a radiation effect of thorium although a chemical toxic effect cannot be ruled out and further investigation of chemical toxicity of rare earths are indicated.

Adult↗
PubMed2005

Validating an important aspect of the new ICRP biokinetic model of thorium.

The daily urinary excretion of Th (Th) was estimated in 11 adult German subjects who were not exposed occupationally to thorium and its related compounds. Thirty-one urine samples were collected over 24-h periods on different occasions from these subjects and were analyzed using high resolution sector field inductively coupled plasma mass spectrometry (HR-SF-ICP-MS). Using this instrument a limit of detection of 20 pg L for thorium in the reagent blank was achieved. The median (mean) daily urinary thorium excretion was obtained as 1.0 (1.8) ng. This was in good agreement with the mean value of 1.5 ng Th (6 microBq) reported by another group for German population, but is significantly lower in comparison to the daily excretion range of 3.6 to 105 ng reported from other countries. The expected daily urinary excretion of thorium for the adult German population was also calculated by applying the new ICRP biokinetic model of thorium assuming reference intake values. The expected urinary thorium excretion rate for this age group is about 0.1 ng per day. Even if a small contribution from the inhalation is considered, the calculated value will be much lower than the measured values. The reason for the disagreement appears to be the use of a low gastrointestinal absorption factor (f1) of 5 x 10 in the ICRP model. Based on the present study, a higher f1 factor might be proposed separately for dietary incorporated thorium.

Adult↗