Concentrations of natural radionuclides in imported mineral substances

Levels of natural radionuclides, such as thorium-232 (232Th), radium-226 (226Ra) and potassium-40 (40K), were determined in about 2,000 samples of imported mineral substances using gamma spectrometry. The maximum concentration levels of 232Th, 226Ra and 40K were 1,260 +/- 54, 13,400 +/- 94 and 1,256 +/- 260 Bq kg(-1), respectively, in zirconium compounds. Due to relatively high concentrations of the above-mentioned radionuclides in some imported mineral substances, the National Radiation Protection Department (NRPD), as the competent authority, has established national limits (900 Bq kg(-1) for 232Th, 1800 Bq kg(-1) for 226Ra and 11,000 Bq kg(-1) for 40K), based on the external exposures, for general importation permits of these materials.     

Norm and associated radiation hazards in bricks fabricated in various localities of the North-West Frontier Province (Pakistan).

The activity concentrations of natural gamma-emitting radionuclides and associated radiation hazards due to 40K, 226Ra and 232Th have been measured in baked brick samples, collected from six highly populated areas of the North-West Frontier Province (NWFP) of Pakistan. For the detection, analysis and data acquisition, a high purity germanium (HPGe) detector coupled with a high resolution multichannel analyser (MCA) was used. The range of the average values of the activity concentrations due to 40K, 226Ra and 232Th were found to be 680.3 +/- 22.2-784.4 +/- 30.7 Bq kg(-1), 36.9 +/- 3.5-51.9 +/- 3.3 Bq kg(-1) and 52.5 +/- 3.6-67.6 +/- 3.1 Bq kg(-1), respectively. Radium equivalent (Ra(eq)) activities and various hazard indices were also calculated to assess the radiation hazards. All the brick samples showed Ra, activities within the limit (370 Bq kg(-1)) set by the Organization for Economic Cooperation and Development (OECD) countries. The results of different criterion formulae also complemented each other in this study. The derived data have been compared with the reported values for other countries of the world.     

Assessment of natural and anthropogenic radioactivity levels in rocks and soils in the environs of Swieradow Zdroj in Sudetes, Poland, by in situ gamma-ray spectrometry

The natural radioactivity of 40K, 208Ti, 212Pb, 214Pb, 228Ac, and the fallout of 137Cs in typical rocks and soils of Swieradów Zdrój area (Sudetes Mountains, Poland) were measured in situ using a portable gamma-ray spectrometry workstation. The measurement points were chosen for different regional lithology: within hornfelses of the Szklarska Poreba schist-belt, quartz rocks, gneisses of the Swieradów Zdrój unit, leucogranites, leptinites, mica schists of the Stara Kamienica belt, and finally the zones of the southern and northern contacts of the Stara Kamienica schist-belt with leucogranites and gneisses of the Lesna unit, respectively. 40K activity varied in the range from about 320 Bq kg(-1) (quartz) to 1200 Bq kg(-1) (gneisses). The activity concentrations associated with 228Ac (232Th series) varied in the range from 25 Bq kg(-1) (quartz) to 62 Bq kg(-1) (leucogranites), whereas activity concentration of 226Ra varied in the range from about 31 Bq kg(-1) (hornfelses) to 122 Bq kg(-1) (leucogranites). Relatively low deposits of 137Cs were noted in the investigated area, where the activity concentrations ranged from 4001 (hornfelses) Bq m(-2) to less than 154 Bq m(-2) (leucogranites).     

Natural radioactivity measurements in the city of Ptolemais (Northern Greece)

Specific activities of the natural radionuclides (238)U, (226)Ra, (232)Th and (40)K were measured by means of gamma-ray spectrometry in surface soil samples collected from the city of Ptolemais, which is located near lignite-fired power plants. The mean activity values for (238)U, (226)Ra, (232)Th and (40)K were found to be 42+/-11, 27+/-6, 36+/-5 and 496+/-56 Bq kg(-1), respectively. These values fall within the range of typical world and Greek values for soil. The indoor radon concentration levels, which were also measured in 66 dwellings by means of SSNTD, ranged from 12 to 129 Bq m(-3), with an average value of 36+/-2 Bq m(-3). This value is close to world and Greek average values for indoor radon concentrations. The total effective dose due to outdoor external irradiation of terrestrial origin and to indoor internal irradiation from the short-lived decay products of (222)Rn was estimated to be 1.2 mSv y(-1) for adults, which is lower than the global effective dose due to natural sources of 2.4 mSv y(-1).     

Radium equivalent activity concentrations in concrete building blocks in eight cities in Southwestern Nigeria

The radioactivity concentrations of (226)Ra, (232)Th and (40)K were measured by using gamma ray spectroscopy in 130 concrete building blocks collected from block making sites in eight cities in Southwestern Nigeria. The results were used to compute the radium equivalent activity concentration for each city. The values of the concentrations of the primordial radionuclides varied widely within each city and among the cities. The weighted means for the cities range between 13.3 and 18.4, 28.2 and 71.6, and 176.2 and 336.8 Bq/kg for (226)Ra, (232)Th and (40)K, respectively. The city weighted means of radium equivalent activity concentrations for the eight cities range from 81 to 145 with a mean of 101 Bq/kg. The maximum for external hazard index was determined as 0.39. All the values are within the safety limits recommended by UNSCEAR [United Nations Scientific Committee on the Effects of Atomic Radiation 1982. Report to the General Assembly, with annexes. New York, United Nations.].     

Natural radioactivity in farm soil and phosphate fertilizer and its environmental implications in Qena governorate, Upper Egypt

Samples of phosphate fertilizers and farm soils, taken to a depth of up to 30 cm in cultivated land, were collected over the Qena governorate, Upper Egypt. Activity concentration of background radionuclides such as (226)Ra, (232)Th and (40)K of these samples were determined by gamma-ray spectrometry. The results show that these radionuclides were present in concentrations of 366+/-10.5, 66.7+/-7.3 and 4+/-2.6 Bq/kg for phosphate fertilizers. For farm soil and Nile island's soil the corresponding values were 13.7+/-7, 12.3+/-4.6, 1233+/-646 and 11.9+/-6.7, 10.5+/-6.1, 1636+/-417 Bq/kg, respectively. The radium equivalent activity (Ra(eq)), the representative level index, I(gamma r), and absorbed dose in air for all samples were calculated. The data were discussed and compared with those given in the literature.     

Aerial measurements on uranium ore mining, milling and processing areas in Germany

The paper describes aerial measurements at several sites containing residues from uranium mines, waste rock dumps and tailings ponds of the Wismut company in Saxony and Thuringia. For the measurements, a computerized gamma-ray spectrometer equipped with a HPGe-detector and a NaI(Tl)-detector array with a volume of 121 was used. Radioactive anomalies from natural radionuclides have been detected and mapped. The activity concentrations of 226Ra, 228Th and 40K in areas with elevated radioactivity from natural radionuclides were determined from aerial measurements. Ground-based measurements--as far as available--confirmed these results. The mean 226Ra activity concentrations in the different waste rock dumps were found to be in the range 370 to 1600 Bq kg-1. The highest mean 226Ra activity concentrations were measured for the tailings ponds with values up to 1300 Bq kg-1. For 40K and 208Tl, activity concentrations of 860 and 40 Bq kg-1, respectively, were obtained as averages of all measurements. These values are commonly found in the environment. In general, there is reasonable agreement between the results measured with different detectors and measuring methods.     

Soil to leaf transfer factor for the radionuclides ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr at Kaiga region, India

Transfer factors are the most important parameters required for mathematical modeling used for environmental impact assessment of radioactive contamination in the environment. In this paper soil to leaf transfer factor for the radionuclides ⁴⁰K, ²²⁶Ra, ¹³⁷Cs and ⁹⁰Sr is estimated for Kaiga region in Karnataka state, India. Among the plants in which study is carried out, ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr activity in leaves of herbaceous plants is higher than that of tree leaves. Soil to leaf transfer factor for ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr was found to be in the range of 0.03-0.65, 0.32-8.04, 0.05-3.03 and 0.42-2.67 respectively.     

Distribution of gamma-ray emitting radionuclides in the environment of Burullus Lake: I. Soils and vegetations

The concentrations and distribution of gamma-ray emitting isotopes in Burullus Lake were investigated with the aim of evaluating the environmental radioactivity. Particularly in wetlands, natural properties of the environment can cause the actual inventory to be different from the activity originally deposited. The mean concentrations of (226)Ra, (232)Th and (40)K were 14.3, 15.5 and 224 Bq/kg, respectively, in the coastal soils. On the other hand, soil samples from the islands had mean concentrations of 13.5, 17.4 and 341 Bq/kg for (226)Ra, (232)Th and (40)K, respectively. Samples from coast and islands show evidence of possible transfer and accumulation of the (137)Cs radionuclide. The mean (137)Cs activity concentrations in the soil samples were 1.2 and 15.1 Bq/kg in the coast and islands, respectively. The vertical migration of (137)Cs was studied based on its content in the consequently located three soil layers down to 30 cm depth. The radium equivalent, dose rate in air and annual dose equivalent from the terrestrial natural gamma-radiation were evaluated. The mean activity concentrations of the gamma-ray emitting radionuclides in vegetation were relatively low.     

Characteristics, spatial distribution and vertical profile of gamma-ray emitting radionuclides in the coastal environment of North Sinai

Radionuclide concentrations of beach and dune sand from various sites in Al-Arish city and surrounding area, North Sinai, Egypt, were measured. The sampling sites included locations in the local harbor, Al-Arish valley and Zaranik protected area. The results indicate that the activities of the products of (232)Th and (226)Ra series in samples from the harbor and along the beach were higher than those from non-coastal sites. The activity concentrations of (232)Th for beach sand ranged from 2.3 to 506.5 Bq/kg with an average of 83.4 Bq/kg, while that for dune sand ranged from 2.2 to 15.1 Bq/kg with an average of 6.4 Bq/kg. The average activity concentration of (226)Ra for beach sand was 56.0 Bq/kg (2.9-261.5 Bq/kg), while that for dune sand was 6.5 Bq/kg (3.0-14.7 Bq/kg). The average activity concentrations of (40)K for beach and dune sand were 88.1 Bq/kg and 178.4 Bq/kg, respectively. Six depth profiles in the harbor area were measured up to a depth of 1m within more than two years. These sets of measurements allowed the determination of the migration rate of black sand to be 0.094 cm/day. Samples with the smallest grain size (<0.2 mm) were found to have the highest level of activities, which were attributed to their high content of black sand. No risk exists for public health based on the calculated effective dose equivalent and the recommended limit of 5 mSv/y. On the other hand, local children and adults may receive doses higher than this recommended limit in two locations in the Zaranik protected area according to a model developed in this study.     

Natural radioactivity measurements in building materials in Southern Lebanon

Using gamma-spectroscopy and CR-39 detector, concentration C of naturally occurring radioactive nuclides (226)Ra, (222)Rn, (214)Bi, (228)Ac, (212)Pb, (212)Bi and (40)K, has been measured in sand, cement, gravel, gypsum, and paint, which are used as building materials in Lebanon. Sand samples were collected from 10 different sandbank locations in the southern part of the country. Gravel samples of different types and forms were collected from several quarries. White and gray cement fabricated by Shaka Co. were obtained. gamma-spectroscopy measurements in sand gave Ra concentration ranging from 4.2+/-0.4 to 60.8+/-2.2 Bq kg(-1) and Ra concentration equivalents from 8.8+/-1.0 to 74.3+/-9.2 Bq kg(-1). The highest Ra concentration was in gray and white cement having the values 73.2+/-3.0 and 76.3+/-3.0 Bq kg(-1), respectively. Gravel results showed Ra concentration between 20.2+/-1.0 and 31.7+/-1.4 Bq kg(-1) with an average of 27.5+/-1.3 Bq kg(-1). Radon concentration in paint was determined by CR-39 detector. In sand, the average (222)Rn concentration ranged between 291+/-69 and 1774+/-339 Bq m(-3) among the sandbanks with a total average value of 704+/-139 Bq m(-3). For gravel, the range was found to be from 52+/-9 to 3077+/-370 Bq m(-3) with an average value of 608+/-85 Bq m(-3). Aerial and mass exhalation rates of (222)Rn were also calculated and found to be between 44+/-7 and 2226+/-267 mBq m(-2)h(-1), and between 0.40+/-0.07 and 20.0+/-0.3 mBq kg(-1)h(-1), respectively.     

Vertical profiles and enrichment pattern of natural radionuclides in monazite areas of coastal Kerala

Detailed studies on radionuclides concentration in different environmental matrices of high background areas were undertaken in the coastal areas of Karunagapalli, Chavara, Neendakara and Kollam to study the distribution and enrichment of the radionuclides in the region. The sand samples collected at different distances from sea waterline and at different depths, were analysed for primordial radionuclides by gamma spectrometry. The activity of primordial radionuclides was determined for the different size fractions of sand to study the enrichment pattern. The highest activity was found confined in 125-63 microm particle size fraction in sand. The minimum (232)Th activity was 9.4 Bq kg(-1), found in Kollam at a depth of 10-20 cm, 40 m away from waterline in 500-250 microm particle size fraction and maximum activity of 136,811.2 Bq kg(-1) was observed in Chavara in grains of size 125-63 microm at a depth of 0-10 cm for a sample collected 20 m away from waterline. The lowest (226)Ra activity observed was 29.6 Bq kg(-1) at Kollam beach for a sample 40 m away from waterline in grains of size 1000-500 microm and at a depth of 20-30 cm and the highest activity observed was 10,309 Bq kg(-1) in grains of size 125-63 microm for a sample collected at a distance 20 m away from waterline and at a depth of 0-10 cm. The activity of (40)K was below detectable level in most of the samples collected from the high background monazite area. The (232)Th, (226)Ra activities decrease with depth for the samples collected 20 m away from the waterline and increase with depth for the samples collected 40 m away from the waterline at Chavara and Kollam beaches. No definite correlation was found between variation of the concentrations of (232)Th and (226)Ra with depth at Karunagapalli and Neendakara beach sands. There exists a strong correlation between (226)Ra and (232)Th activities in the region. The results of these investigations are presented and discussed in this paper.     

Environmental characterization and radio-ecological impacts of non-nuclear industries on the Red Sea coast

The Red Sea is a deep semi-enclosed and narrow basin connected to the Indian Ocean by a narrow sill in the south and to the Suez Canal in the north. Oil industries in the Gulf of Suez, phosphate ore mining activities in Safaga-Quseir region and intensified navigation activities are non-nuclear pollution sources that could have serious radiological impacts on the marine environment and the coastal ecosystems of the Red Sea. It is essential to establish the radiological base-line data, which does not exist yet, and to investigate the present radio-ecological impact of the non-nuclear industries to preserve and protect the coastal environment of the Red Sea. Some natural and man-made radionuclides have been measured in shore sediment samples collected from the Egyptian coast of the Red Sea. The specific activities of 226Ra and 210Pb (238U) series, 232Th series, 40K and 137Cs (Bq/kg dry weight) were measured using gamma ray spectrometers based on hyper-pure germanium detectors. The specific activities of 210Po (210Pb) and uranium isotopes (238U, 235U and 234U) (Bq/kg dry weight) were measured using alpha spectrometers based on surface barrier (PIPS) detectors after radiochemical separation. The absorbed radiation dose rates in air (nGy/h) due to natural radionuclides in shore sediment and radium equivalent activity index (Bq/kg) were calculated. The specific activity ratios of 228Ra/226Ra, 210Pb/226Ra, 226Ra/238U and 234U/238U were calculated for evaluation of the geo-chemical behaviour of these radionuclides. The average specific activity of 226Ra (238U) series, 232Th series, 40K and 210Pb were 24.7, 31.4, 427.5 and 25.6 Bq/kg, respectively. The concentration of 137Cs in the sediment samples was less than the lower limit of detection. The Red Sea coast is an arid region with very low rainfall and the sediment is mainly composed of sand. The specific activity of 238U, 235U and 234U were 25.3, 2.9 and 25.0 Bq/kg. The average specific activity ratios of 226Ra/228Ra, 210Pb/226Ra and 234U/238U were 1.67, 1.22 and 1.0, respectively. The relationship between 226Ra/228Ra activity ratio and sample locations along the coastal shoreline indicates the increase of this ratio in the direction of the Shuqeir in the north and Safaga in the south where the oil exploration and phosphate mining activities are located. These activities may contribute a high flux of 226Ra. The concentration and distribution pattern of 226Ra in sediment can be used to trace the radiological impact of the non-nuclear industries on the Red Sea coast.     

Natural radioactivity and dose assessment for phosphate rocks from Wadi El-Mashash and El-Mahamid Mines, Egypt

The activity concentrations of (226)Ra, (232)Th and (40)K have been measured by gamma spectroscopy (sodium iodide NaI(Tl) detector) in phosphate rock samples, collected from the Wadi El-Mashash, a site located in the central eastern desert, and El-Mahamid in the Nile valley, Egypt. The average activity concentrations of (226)Ra, (232)Th and (40)K (Bq kg(-1)) in phosphate rocks were 665.8+/-33.4, 329.4+/-17 and 587.6+/-29.4 for Wadi El-Mashash and 566.8+/-28.6, 217.3+/-11.8 and 560.1+/-28 for El-Mahamid, respectively. The corresponding values for shale rocks were 85.2+/-5.7, 93.3+/-5.6 and 303.1+/-15.2 Bq kg(-1), respectively. As a measure of radiation hazard to the occupational workers and public, the Ra equivalent activities, representative level index and dose rates due to natural radionuclides at 1 m above the ground surface were estimated. The calculated external gamma-radiation dose received by the workers of the phosphate mine are 538 and 418 microSv/y, which is far below the permitted dose of 20 mSv/y recommended by the International Commission of Radiation Protection [ICRP-60, 1990. Radiation Protection: 1990 Recommendation of the International Commission on Radiological Protection, Oxford, Pergamon Preis.] for workers.     

Distribution of (226)Ra-(210)Pb-(210)Po in marine biota and surface sediments of the Red Sea, Sudan

Activity concentration levels and ratios of (226)Ra, (210)Pb and (210)Po are presented in multicellular marine algae, molluscs, coral as well as in surface marine sediments collected from the shallower waters of the fringing reefs area extending towards north and south (Flamingo bay) of PortSudan harbour, Sudan. The analyses were performed adopting alpha-spectrometry, liquid scintillation and Cerenkov counting techniques. Surface sediments from this coastal region are poor in their radioactivity content in contrast to similar data reported from different coastal areas around the globe. There is surface enrichment of (210)Pb and (210)Po with respect to their progenitor (226)Ra as it is evident from the activity ratios of (210)Pb/(226)Ra (3.03+/-1.79) and (210)Po/(226)Ra (2.23+/-1.56). Among marine plants and animals investigated, the green algae species, Halimeda, and coral species, Favites, show substantial concentration of radium at 8.2Bq/kg and 21.9Bq/kg dry weight, respectively. Similarly, the highest concentration of (210)Po was met in Favites at 38.7Bq/kg followed by brown algae, Cystoseria sp., at 32.6Bq/kg. There is no variation seen among algal species for (210)Pb uptake, however, converse to radium and polonium, Favites (coral) was found to contain the minimum concentration of lead (3.88Bq/kg). In most species there is preferential accumulation of polonium over its parent radium as indicated by (210)Po:(226)Ra activity ratio with Cystoseria (brown algae) showing the highest value at 8.81. On the other hand, (210)Po:(210)Pb activity concentration ratio revealed that coral species Favites (9.97) and the brown algae Sargassum (1.85) have a greater tendency to accumulate (210)Po over (210)Pb, while in the rest of species; this ratio is less than unity.     

The application of phosphogypsum in agriculture and the radiological impact

Radium-226 in phosphogypsum produced in a phosphate industry, SICNG operating at Thessaloniki, Northern Greece since May 1966, varied from 261 to 688 Bq kg(-1) (mean value 508 Bq kg(-1)). This radionuclide in soil tilled with phosphogypsum used for agricultural purposes varied from 50 to 479 Bq kg(-1) (average 205 Bq kg(-1)), while in the regular soil of cultivated fields it varied from 37 to 54 Bq kg(-1) (average 48 Bq kg(-1)). Radium-226 in rice originated from cultivated fields tilled with phosphogypsum or not varied from 0.36 to 1.98 Bq kg(-1) (average 1.53 Bq kg(-1)) with the higher values observed in samples originated from cultivated fields tilled with phosphogypsum. Radium-226 transfer factors, TF, from soil tilled with phosphogypsum to plants for the case of rice varied from 6.5 x 10(-3) to 2.0 x 10(-2) (geometric mean: 1.1 x 10(-2)). A mean (226)Ra content in rice 1.53 Bq kg(-1) results in a daily intake of (226)Ra by humans in Greece 0.0084 Bq day(-1) leading to an annual effective dose for adults 0.86 microSv y(-1) which is much less in contributing to the average exposure to natural radiation sources (2.4 mSv y(-1)) and particularly to the part due to ingestion (0.29 mSv y(-1)). It is necessary to continuously control (monitoring) (226)Ra in phosphogypsum before any use for agricultural purposes.     

Concentrations and environmental fate of Ra in cation-exchange regeneration brine waste disposed to septic tanks and accumulation in sludge, New Jersey Coastal Plain, USA

Concentrations of Ra in liquid and solid wastes generated from 15 softeners treating domestic well waters from New Jersey Coastal Plain aquifers (where combined Ra ((226)Ra plus (228)Ra) concentrations commonly exceed 0.185 Bq L(-1)) were determined. Softeners, when maintained, reduced combined Ra about 10-fold (<0.024 Bq L(-1)). Combined Ra exceeded 0.185 Bq L(-1) at 1 non-maintained system. Combined Ra was enriched in regeneration brine waste (maximum, 81.2 Bq L(-1)), but concentrations in septic-tank effluents receiving brine waste were less than in the untreated ground waters. The maximum combined Ra concentration in aquifer sands (40.7 Bq kg(-1) dry weight) was less than that in sludge from the septic tanks (range, 84-363 Bq kg(-1)), indicating Ra accumulation in sludge from effluent. The combined Ra concentration in sludge from the homeowners' septic systems falls within the range reported for sludge samples from publicly owned treatment works within the region.     

Radionuclide content of concrete building blocks and radiation dose rates in some dwellings in Ibadan, Nigeria

Thirty-two samples of concrete building blocks were collected from different block making industries in Ibadan. The radioactivity concentrations of the natural radionuclides in the samples were determined by gamma-ray spectrometry with a NaI(Tl) detector. The radioactivity concentrations varied from 6.2 to 57.5 Bq kg(-1), 12.4 to 64.9 Bq kg(-1) and 95.3 to 766.1 Bq kg(-1) for 226Ra, 232Th and 40K, respectively. The radium equivalent activities of the 32 samples varied from 51.3 to 175.7 Bq kg(-1). Radiation exposure levels in 30 dwellings were determined using LiF thermoluminescent dosimeters. The annual equivalent dose rates varied from 0.318 to 0.657 mSv y(-1) with a mean of 0.433 mSv y(-1). The annual effective dose rate to the whole body was calculated as 0.236 mSv y(-1), which is less than that (mean) estimated by UNSCEAR for normal background areas.     

Radiological hazards of Narghile (hookah, shisha, goza) smoking: activity concentrations and dose assessment

Narghile (hookah, shisha, goza, "water-pipe") smoking has become fashionable worldwide. Its tobacco pastes, known as moassel and jurak, are not standardized and generally contain about 30-50% (sometimes more) tobacco, molasses/juice of sugarcane, various spices and dried fruits (particularly in jurak) and, in the case of moassel, glycerol and flavoring essences. Tobacco contains minute amounts of radiotoxic elements such as (210)Pb, (210)Po and uranium, which are inhaled via smoking. Only very few data have been published on the concentrations of natural radionuclides in narghile tobacco mixtures. Consequently, the aim of this study was to draw first conclusions on the potential hazards of radioactivity in moassel tobacco in relation to narghile smoking. The results indicate the existence of a wide range in the radioactivity contents where the average (range) activity concentrations of (238)U, (234)Th (226)Ra, (210)Pb, (210)Po, (232)Th and (40)K, in Bq/kg dry weight were 55 (19-93), 11 (3-23), 3 (1.2-8), 14 (3-29), 13 (7-32), 7 (4-10) and 719 (437-1044)Bq/kg dry weight, respectively. The average concentrations of natural radionuclides in moassel tobacco pastes are comparable to their concentration in Greek cigarettes and tobacco leaves, and lower than that of Brazilian tobacco leaves. The distribution pattern of these radionuclides after smoking, between smoke, ash and filter, is unknown, except for (210)Po during cigarette smoking and from one existing study during moassel smoking. Radiological dose assessment due to intake of natural radionuclides was calculated and the possible radio-toxicity of the measured radionuclides is briefly discussed.     

Biomagnification of 7Be, 234Th, and 228Ra in marine organisms near the northern Pacific coast of Japan

Enrichment of natural radionuclides of thorium, radium and beryllium in several kinds of marine organisms was investigated near the Pacific coast of Miyagi Pref., Japan. The radioactivity of 7Be, 210Pb, 234Th, 238U, 228Ra and 137Cs was measured using gamma spectrometry. High concentrations of 234Th were observed in ascidian livers (50-400 Bq/kg dry) and excrement (2000-2900 Bq/kg dry), although the parent 238U concentrations were less than 3 Bq/kg dry. Such extreme disequilibrium between 238U and 234Th activity was observed in other organisms (barnacles, mussels and brown algae). Relatively high concentrations of 228Ra were detected in ascidian livers and were observed to decrease according to its half-life (5.75 year), suggesting disequilibrium with its parent 232Th. High concentrations (about 1900-5000 Bq/kg dry) of 7Be were detected in ascidian liver. Possible mechanisms for the observed biomagnification and bioaccumulation of these radionuclides in the organisms analyzed were proposed.