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PubMed2002

Assessment of gamma dose rate over a suspected uranium mineralisation area of Jebel Mun, Western Sudan.

This study was conducted at the request of authorities in western Darfour State, to address the public concern about the levels of radioactivity in the area of Jebel Mun situated at Sudan-Chad international boundaries. It has been identified as a high background radiation area through aerial geological surveys conducted in late 1970s. The ambient gamma dose in the area was measured with the aid of a hand-held dose rate meter (Mini-Rad, Series 1000) and the surface rock samples were collected and analysed for their radioactivity content using a high-resolution gamma spectrometry equipped with HPGe with relative efficiency of 18%. The activity concentrations of 238U, 232Th and 40K were found to range from 39-253 Bq.kg(-1), 41-527 Bq.kg(-1) and 77-3027 Bq.kg(-1), respectively. From the values of the standard deviation it was concluded that the activity concentration of the considered primordial radionuclides was highly scattered (localised) which in turn indicates non-uniformity in the geological features and/or formations. 238U activity concentration corresponds to equivalent mass concentration of 7.77+/-6.12 ppm (3.19-20.73 ppm), which is of no economic importance. Samples are enriched in thorium relative to uranium as reflected by the Th:U mass ratio which ranges from 3 to 17. The absorbed dose rate in air as estimated from the measured activity concentrations of the primordial radionuclides using the DRCFs (dose rate conversion factors) falls within the range of 70-522 nGy.h(-1) with an average of 221+/-130 nGy.h(-1). It corresponds to an annual effective dose equivalent averaged of 0.27 mSv. The regression analysis has shown that the correlation between calculated and the measured ambient dose rate is marginally significant (r2 = 0.59). The 232Th series is the major producer of the surface radioactivity followed by 40K as they contribute 48% and 32% of the total absorbed dose, respectively.

Environmental Exposure↗
PubMed2003

Determination of 238U, 234U, 232Th, 228Th, 228Ra, 226Ra and 210Pb concentration in excreta samples of inhabitants of a high natural background area.

The high concentration of uranium and thorium in certain Brazilian areas provides an opportunity to evaluate the radiation exposure due to intake of radionuclides by the populations that live and work in areas with a high natural radiation background. Buena, where this study was conducted, is a small village on the coast in the northern part of Rio de Janeiro State, characterised by the presence of a large deposit of monazite sand. In this paper, the concentrations of 238U, 234U, 232Th, 228Th, 228Ra, 226Ra and 210Pb in faecal samples from inhabitants of this area were determined by a sequential analytical method. The results of the average concentrations in faeces of inhabitants of Buena are 9.4 +/- 3.4 mBq g(ash)(-1) for 238U, 9.2 +/- 4.0 mBq g(ash)(-1) for 234U, 7.0 +/- 4.2 mBq g(ash)(-1) for 232Th, 256.1 +/- 134.6 mBq g(ash)(-1) for 228Th, 335.5 +/- 192.8 mBq g(ash)(-1) for 228Ra, 156.6 +/- 74.1 mBq g(ash)(-1) for 226Ra and 66.7 +/- 17.7 mBq g(ash)(-1) for 210Pb. The results were compared with background concentrations from faecal samples from individuals living in Rio de Janeiro City. For most of the radionuclides analysed, the average concentration in faeces from inhabitants of the high natural radiation background was higher than the concentration found in Rio de Janeiro, considered a 'normal' background area.

Background Radiation↗
PubMed2005

Calibration of an electrostatic chamber for thoron measurements in exhaled breath.

An electrostatic chamber system used for measuring thoron in the exhaled breath of thorium workers is calibrated using a standard thoron source and a scintillation cell counting system. A formulation based on both a streamlined flow model and a well-mixed flow model in the chamber has been made to estimate thoron concentration in breath from the observed alpha counts. The experimental measurements of the ratio of the outlet and the inlet thoron concentrations across the chamber strongly validate the well-mixed flow model for thoron, as against the streamlined flow model. The progeny collection efficiency on the electrode has been found to be 70%. The study points out a major error by a factor of approximately 25 in the calibration factor reported in an earlier work. From the present study, the minimum detectable limit of the activity of (224)Ra, freely emanating thoron at mouth works out to be 0.36 Bq as against 0.014 Bq reported earlier for the same system.

Air Pollutants, Radioactive↗
PubMed2006

Simultaneous measurements of indoor radon, radon-thoron progeny and high-resolution gamma spectrometry in Greek dwellings.

Simultaneous indoor radon, radon-thoron progeny and high-resolution in situ gamma spectrometry measurements, with portable high-purity Ge detector were performed in 26 dwellings of Thessaloniki, the second largest town of Greece, during March 2003-January 2005. The radon gas was measured with an AlphaGUARD ionisation chamber (in each of the 26 dwellings) every 10 min, for a time period between 7 and 10 d. Most of the values of radon gas concentration are between 20 and 30 Bq m(-3), with an arithmetic mean of 34 Bq m(-3). The maximum measured value of radon gas concentration is 516 Bq m(-3). The comparison between the radon gas measurements, performed with AlphaGUARD and short-term electret ionisation chamber, shows very good agreement, taking into account the relative short time period of the measurement and the relative low radon gas concentration. Radon and thoron progeny were measured with a SILENA (model 4s) instrument. From the radon and radon progeny measurements, the equilibrium factor F could be deduced. Most of the measurements of the equilibrium factor are within the range 0.4-0.5. The mean value of the equilibrium factor F is 0.49 +/- 0.10, i.e. close to the typical value of 0.4 adopted by UNSCEAR. The mean equilibrium equivalent thoron concentration measured in the 26 dwellings is EEC(thoron) = 1.38 +/- 0.79 Bq m(-3). The mean equilibrium equivalent thoron to radon ratio concentration, measured in the 26 dwellings, is 0.1 +/- 0.06. The mean total absorbed dose rate in air, owing to gamma radiation, is 58 +/- 12 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 38% due to 40K, 36% due to thorium series and 26% due to uranium series. The annual effective dose, due to the different source terms (radon, thoron and external gamma radiation), is 1.05, 0.39 and 0.28 mSv, respectively.

Air Pollution, Indoor↗
PubMed2006

Radiological characterisation of disposed phosphogypsum in Brazil: evaluation of the occupational exposure and environmental impact.

Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents a serious problem facing the phosphate industry in Brazil. This by-product (mainly calcium sulphate dihydrate) precipitates during the reaction of sulphuric acid with phosphate rock and is stored at a rate of about 4x10(6) kg per day on several piles in Cubatão, Brazil. Contents of natural radionuclides from thorium and uranium series were measured in Brazilian phosphogypsum samples from disposal piles, using high-resolution gamma ray spectrometry and instrumental neutron activation analysis (NAA). These phosphogypsum piles present a potential threat to the surrounding environment and to the individual occupationally exposed. The results obtained in this study show that radionuclides, although present in relatively high concentrations in phosphogypsum, do not imply in significant doses for individuals occupationally exposed. The results obtained for the water activity in the monitor wells showed that the run-off of the piles is influenced by the activity present in the piles, giving indication of a possible groundwater contamination. Sediments from rivers in the area of influence of the pile presented higher concentrations of 238U and 232Th when compared with reference values.

Brazil↗
PubMed2006

Natural radionuclides in zircon and related radiological impacts in mineral separation plants.

The activity concentration of uranium and thorium present in zircon obtained from mineral sand industries are presented. External gamma radiation levels and inhalation of airborne dust are found to be the significant routes of radiation exposure to occupational workers. The annual average dose attributed to zircon processing is estimated to be 2.3 mSv in the plants under study. This paper presents the results of external gamma measurements, estimation of airborne radioactivity in zircon process locations and radon and thoron in the occupational environment of two mineral separation plants in India. Analyses of the solid wastes and liquid effluent generated and resultant environmental impacts are indicated.

Air Pollutants, Radioactive↗
PubMed2006

Unexpectedly high activity of 228Th in excretion samples following consumption of Brazil nuts.

A worker provided a routine faecal sample for plutonium and americium analysis. In the course of this analysis 500 mBq of (228)Th was discovered. There seemed no credible occupational route for intake of thorium. Further investigation revealed that the worker consumed approximately 25 g d(-1) of nuts, including Brazil nuts. A sample of these nuts was analysed and found to contain activities of (228)Th in sufficient quantity to account for the faecal activity. However, follow-up urine samples taken from the worker showed 0.6-0.7 mBq of (228)Th. The intake of (228)Th via nuts is insufficient to account for this activity in urine. However, it is likely that the intake of (228)Th was accompanied by similar activity of the parent (228)Ra, and biokinetic calculations show that decay of (228)Ra in vivo would produce sufficient (228)Th to account for the observed urine activity.

Adult↗
PubMed2006

Natural radioactivity intake into wheat grown on fertilized farms in two districts of Pakistan.

The use of phosphate fertilizers on agricultural farms enhances gamma-ray activity concentration in the farms and therefore absorbed dose rates to the public. The most common natural radionuclides in fertilizer and soil are (40)K, (226)Ra and (232)Th. Agricultural farms at four locations in two districts in Pakistan consisting of saline and normal soils had been under fertilizer treatment for the past 30, 20, 10 and 0 y, therefore, natural radioactivity has been measured in soil samples from these sites to investigate the effect of fertilizers in soil and wheat grown in these sites. Radioactivity measured in soil of the sites under investigation was 550-644, 20-35 and 42-58 Bq kg(-1) for (40)K, (226)Ra and (232)Th, respectively. Wheat was grown in the farms and radioactivity transferred from soil to roots, shoots and grains was also measured. Relatively high natural radioactivity has been observed in the fertilized agricultural farms and in the wheat plants grown in these farms. From the total amount of an element uptaken in a plant, distribution of the element in different parts of the plant has been studied. The distribution of potassium was almost uniform in roots, shoots and grains of wheat; that of radium was different in the three parts of wheat; and that of thorium was almost equal in shoots and grains but quite large in the roots. Soils to grain transfer factors of the natural radionuclides have been determined as 3-4 x 10(-2) for (226)Ra, 2-3 x 10(-2) for (232)Th and 17-20 x 10(-2) for (40)K. Annual doses of (40)K and (226)Ra received by intake of grain products have been estimated to lie within range while the dose received from intake of (232)Th is larger than the range specified in UNSCEAR report 2000.

Environmental Exposure↗
PubMed1983

Effects of Thorotrast in humans.

Thorotrast, a patented radiological contrast medium that was widely used from 1930-1950, is a thorium dioxide colloid that has been neutralized and stabilized by protective colloids, which are decomposition products of starch, and which are now generally known as dextrans. The deposition of Thorotrast depends on its radiological use, its method of preparation, and the age of the preparation; however, the major site is the reticulo-endothelial system, where it is retained for long times. Some of its decay products, principally 228Ra and 224Ra, escape from the colloidal particles and deposit in the skeleton. The biological end-points that have been observed in the several human populations that are known to have received Thorotrast are Thorotrastomas, malignant hepatic neoplasms, and other neoplasms of the reticulo-endothelial system (RES), skeletal sarcomas, and leukemias in excess of the number expected. The question to be reviewed in this paper is whether irradiation, or chemical and mechanical effects on the reticulo-endothelial system, or a combination thereof, is the causative factor in the occurrence of these RES neoplasms.

Aluminum↗
PubMed1989

An assessment of soil-to-plant concentration ratios for some natural analogues of the transuranic elements.

A field study was conducted in an area of enhanced, natural radioactivity to assess the soil to edible vegetable concentration ratios (CR = concentration in dry vegetable/concentration in dry soil) of 232Th, 230Th, 226Ra, 228Ra, and the light rare earth elements (REE's) La, Ce and Nd. Twenty-nine soil and 42 vegetable samples consisting of relatively equal numbers of seven varieties were obtained from 11 farms on the Pocos de Caldas Plateau in the state of Minas Gerais, Brazil. This region is the site of a major natural analogue study to assess the mobilization and retardation processes affecting Th and the REE's at the Morro do Ferro ore body and U series radionuclides at a nearby open pit U mine. Thorium (IV) serves as a chemical analogue for quadrivalent Pu and the light REE's (III) as chemical analogues for trivalent Am and Cm. The geometric mean CR's (all times 10(-4] decreased as 228Ra (148) greater than 226Ra (76) greater than La (5.4) greater than Nd (3.0) = Ce (2.6) greater than 232Th (0.6), or simply as M (II) greater than M (III) greater than M (IV). These differences may reflect the relative availability of these metals for plant uptake. Significant differences were found in the CR's (for any given analyte) among many of the vegetables sampled. The CR's for the different analytes were also highly correlated. The reasons for the correlations in CR's seen among elements with such diverse chemistries as Ra-REE or Ra-Th are not clear but are apparently related to the essential mineral requirements or mineral status of the different vegetables sampled. This conclusion is based on the significant correlations obtained between the Ca content of the dried vegetables and the CR's for all of the elements studied.

Background Radiation↗
PubMed1992

Clinical consequences of Thorotrast in a long-term survivor.

Thorotrast, a colloidal suspension of 252Th dioxide, was widely used as a radiographic contrast medium for more than 25 y after its clinical practice introduction in 1930. Its excellence as a contrast medium was ultimately eclipsed by its long-term associated morbidities, and its use essentially ended by 1954. This case history presents the clinical events in the last 10 y of life in a patient injected with Thorotrast in 1953. This patient developed three previously described Thorotrast-associated morbidities: pneumococcus sepsis due to functional asplenia and reticuloendothelial system blockade, an enlarging Thorotrastoma (inflammatory mass) at the injection site, and a fatal blood dyscrasia. In addition, she developed three clinical syndromes where a Thorotrast association may exist. She suffered from severe spinal column osteoarthritis and vertebral collapse. An abnormal bone-density measurement implies the presence of radiodense radioactive thorium or its degradation products as potentially responsible. She had evidence of chronic immune system disregulation with immunoglobulin excess, auto antibodies, and cell-mediated immunity deficiency. This condition is similar to that found in patients infected with human immunodeficiency virus and may suggest a shared etiology in reticuloendothelial system damage. Lastly, she developed dense bilateral cataracts. This case history illustrates the temporal relationship of a variety of symptoms. Discussion is directed at review of previous data and support for new associations.

Aged↗
PubMed1992

Whole-body pathologic analysis of a patient with Thorotrast-induced myelodysplasia.

An autopsy was performed on a 72-y-old Caucasian female who had received a carotid artery injection of thorium dioxide in 1953. The body was dissected in such a manner as to provide for radiobiological evaluation as well as to determine histologically the distribution of Thorotrast in the tissues and its complications. Thorotrast was identified within the liver, spleen, lymph nodes, bone marrow, and surrounding the right carotid artery (the injection site). The cause of death was gastric hemorrhage complicating pancytopenia secondary to refractory anemia with excess of blasts (myelodysplastic syndrome).

Aged↗
PubMed1992

The distribution of Thorotrast in human bone marrow: a case report.

Samples of bone containing cellular and fatty bone marrow were removed at autopsy from the body of a woman who, following an automobile accident, had been injected with approximately 25 mL of the radiographic contrast medium Thorotrast. The woman survived for 36 y after the accident and died at age 72 y following bone marrow failure. The samples were analyzed to determine their thorium content by x-ray fluorescence and by image analysis. In addition, Thorotrast was visualized in the different bones examined by light microscopy and by backscattered electron imaging with a scanning electron microscope. The results showed Thorotrast to be largely restricted to areas of cellular bone marrow. In such regions, Thorotrast was present throughout the marrow tissue and was also concentrated within cells that were commonly aggregated within focalized areas of the marrow. Overall the results suggest a rather uniform pattern of Thorotrast uptake by the red bone marrow at different skeletal sites. Significant deposits of Thorotrast were not found in fatty yellow marrow. We conclude that Thorotrast-derived risk estimates for human leukemia following high LET, alpha irradiation may be used for calculating the risks of alpha exposure, but with caution.

Aged↗
PubMed1992

Cancer risk following exposure to Thorotrast: overview in relation to a case report.

Radioactive measurements and histopathologic findings are described in a patient administered Thorotrast, a radiographic contrast agent, 36 y prior to death and compared with cancer risks noted in epidemiologic studies. This person [designated as U.S. Uranium Registry (USUR) Case 1001] had prearranged for donation of her body to the USUR and the National Cancer Institute for study. Elevated levels of radioactivity were noted in those organs in which excess cancers have been reported in epidemiologic surveys of Thorotrast-exposed subjects. Hepatic tissue in USUR Case 1001 was estimated to have received an average lifetime absorbed dose of 16.2 Gy, based on radiochemical analyses, consistent with the high risks for liver tumors reported in all studied populations. Thorotrast was present throughout the bone marrow of USUR Case 1001, who died secondary to complications of refractory anemia with excess blasts (RAEB). Elevated risks for acute myeloid leukemia have been noted in Thorotrast patients, and more recently, cases of RAEB and RAEB in transformation have been reported. The thorium decay series includes the bone-seeking radionuclides 224Ra and 228Ra, which have been associated with high risks for osteosarcomas, although the association between Thorotrast and bone cancer is not as convincing. The skeleton of USUR Case 1001, however, contained significant levels of radioactivity. Other tissues evaluated in USUR Case 1001 included lung, eye, kidney, and breast, which did not contain elevated levels of radioactivity.

Aged↗
PubMed1994

Radiation protection and radioactive scales in oil and gas production.

Low specific-activity scales consisting of alkaline earth metal carbonates and sulfates are often present in some gaseous and liquid hydrocarbon plants. These scales contain a certain concentration of radium, uranium, and thorium which can cause a risk of gamma irradiation and internal radiocontamination when they must be mechanically removed. The gamma dose rates and the 238U, 232Th, 226Ra concentrations were determined in sludges, scales, and waters of some gas and oil hydrocarbon plants located in Italy, Congo, and Tunisia. 238U and 232Th concentrations were were low. The isotopes 238U and 234U resulted in radioactive equilibrium, while 232Th and 228Th were not always equilibrium. A rough correlation was found between the gamma dose rate and the 226Ra concentration. Some considerations and conclusions about radiation protection problems are pointed out.

Fossil Fuels↗
PubMed1995

Measurements of 220Rn emanation from rocks.

Alpha-particle and gamma-ray measurements are employed to determine the individual emanation and production rates associated with the thorium radioactive series for thirty-seven rock specimens of approximately 200 cm3 individual volume representing igneous, sedimentary, and metamorphic types. These results are combined to establish 220Rn emanating powers for each of these specimens, and a wide range of values is observed. The generally large 220Rn emanation observed for these specimens strongly indicates that non-tortuous diffusion paths are commonly present in the associated structures, which gives more evidence for the existence of well-connected pore networks at the nanometer level in many of the specimens studied. While the results are qualitatively explainable, they are not predictable in terms of the current macroscopic observables. Since 220Rn and 222Rn emanation rates from rock specimens have previously been found to be comparable in magnitude, the relatively fast determination of 220Rn emanation rates described herein (measurements involving 1-h duration) is in reasonable probability indicative of a comparable 222Rn emanation rate: The employment of 220Rn as a convenient screening tool for potentially high 222Rn emanation sources is indicated.

Alpha Particles↗
PubMed1999

Calculations of background beta-gamma radiation dose through geologic time.

Life on earth is exposed to a background level of ionizing radiation from a number of sources, including beta and gamma radiation from geologic and biologic materials. Radiation dose from geologic emitters has changed because of the chemical evolution of the continental crust, changes in the relative abundances of 235U and 238U, and the radioactive decay of uranium, thorium, and 40K with time. The radiation dose from internal 40K has decreased by a factor of about eight because of changes in the activity concentration of 40K in potassium over the past 4 billion years. Radiation exposure from geologic materials has decreased from about 1.6 mGy y(-1) to 0.66 mGy y(-1) over the past 4 billion years, and radiation exposure to an organism with a potassium concentration of 250 mmol L(-1) has decreased from about 5.5 to about 0.70 mGy y(-1). Accordingly, background radiation exposure from these two sources has dropped from about 7.0 to 1.35 mGy y(-1) during the time life has existed on Earth. The conservative nature of mutation repair mechanisms in modern organisms suggest that these mechanisms may have evolved in the distant past and that organisms may retain some of the capability of efficiently repairing damage from higher radiation levels than exist at present.

Beta Particles↗
PubMedDate not supplied

Visceral CT findings associated with Thorotrast.

Plain radiography and CT of the abdomen were reviewed in four patients who had undergone angiography with thorium dioxide (Thorotrast). In three patients CT showed irregularly scattered focal punctate collections of Thorotrast in the liver parenchyma, predominantly in the subcapsular zone, associated with areas of low or nonhomogeneous attenuation. These areas of low attenuation were identified on microscopic studies as sites of hepatic fibrosis or neoplasia. Computed tomography identified intrahepatic Thorotrast deposits more definitively than plain radiography.

Aged↗