Evaluation of technologically enhanced natural radiation near the coal-fired power plants in the Lodz region of Poland

Radionuclide releases together with escaping fly ashes (from 45 x 10(6) kg in previous decades to 8 x 10(6) kg annually in 1996) from the main local and several small coal-fired power plants resulted in a relatively small increase in natural radioactivity levels in the Lodz region. The natural gamma terrestrial radiation dose rates (1 m above ground level) were measured at 82 points including in the vicinity of power plants, in the center of the town and on edge of the town. The average dose rate value for the first area was 36 +/- 1.2 nGy h (-1), whereas the same dose rate for the edge of town was slightly lower 30 +/- 0.9 nGy h (-1) but this difference was statistically significant. Further confirmation of the technologically slightly enhanced exposure of the local population to natural radionuclides was achieved by gamma-spectrometry measurement of the uranium and thorium decay series radionuclides in the surface soil profiles (up to 30 cm depth). The average increase of 226Ra and 232Th radionuclides in the top layer of soil (0-10 cm) according to the 20+/-30 cm depth layer was 21% and 17%, respectively. However, due to the relatively low levels of 232Th (14.3 Bq kg (-1)) and 238U (16.8 Bq kg (-1)) in this area, the annual average effective dose from the natural terrestrial radiation for the local population is also relatively low, 0.28 mSv only.     

Photon attenuation, natural radioactivity content and radon exhalation rate of building materials

High concentrations of natural radionuclides in building materials can result in high dose rates indoors, from both internal and external exposure. In dose calculations, the main radionuclides of interest are 226Ra, 232Th and 40K. Usually much attention is paid to 226Ra due to 222Rn exhalation and the subsequent internal exposure. Other radionuclides of the uranium series such as 238U and 210Pb, emitting low energy photons are not usually determined and an assumption of radioactive equilibrium is made. The above assumption is seldom checked mainly because of the difficulties in the gamma-spectroscopic analysis of low energy photons. For the determination of radionuclides emitting low-energy photons, in samples like building materials where intense self-absorption of the photons exists, a method for self-absorption correction has been developed. The method needs as input the linear attenuation coefficient mu for the material under analysis. This paper presents: 1. Correlations in the form mu = f(rho,E) developed for the estimation of the linear attenuation coefficient mu (cm(-1)), as a function of the material packing density p (g cm(-3)) and the photon energy E (keV), for building materials as well as other materials of environmental importance. 2. Gamma-spectroscopic analysis techniques used for the determination of 238U, 226Ra, 210Pb, 232Th and 40K in environmental samples, together with the results obtained from the analysis of building materials used in Greece, and industrial by-products used for the production of building materials. Among the techniques used, one is based on the direct determination of 226Ra and 235U from the analysis of the multiplet photopeak at approximarely186 keV. 3. Results from radon exhalation measurements of building materials such as cement and fly-ash and building structures conducted in the radon chambers in our Laboratory. Based on the above results, dosimetric calculations are also reported.     

Radiological impact from atmospheric releases of 238U and 226Ra from phosphate rock processing plants

Phosphate rocks are used extensively, mainly as a source of phosphorus for fertilizers and secondarily for phosphoric acid and other speciality chemicals. Phosphates are typically enriched in uranium and are thus one of the sources of technologically enhanced natural radiation (TENR) which increases exposure to man from natural radionuclides. Emissions from phosphate rock processing plants in gaseous and particulate form contain radionuclides, such as 238U and 226Ra, which are discharged into the environment causing radiation exposures to the population. About 10 MBq each of 238U and 226Ra are discharged into the environment each year from SICNG, a phosphate rock processing plant in Thessaloniki area, Northern Greece. The collective dose commitment to lung tissue resulting from atmospheric releases was estimated to be approximately 2 x 10(-9) person Gy t-1 for 238U and approximately 0.1 x 10(-9) person Gy t-1 for 226Ra, i.e. about 2 times higher than that estimated in the UNSCEAR reports issued in 1982, 1988, and 1993.     

Soil-to-plant transfer factors for natural radionuclides and stable elements in a Mediterranean area

The transfer factors (TF) for natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 228Th), and 226Ra were obtained in plant samples (grass-pasture) growing in granitic and alluvial soils around a disused uranium mine located in the Extremadura region in the south-west of Spain. Affected and non-affected areas of the mine presented large differences in the activity concentrations of radionuclides of the uranium series. We also determined transfer factors for several stable elements (essential and non-essential). A set of statistical tests were applied to validate the data. The results showed that the transfer factors for both the natural radionuclides and the stable elements are independent of the two substrate types involved and also of the two areas considered in the study.     

Radionuclides from past uranium mining in rivers of Portugal

During several decades and until a few years ago, uranium mines were exploited in the Centre of Portugal and wastewaters from uranium ore milling facilities were discharged into river basins. To investigate enhancement of radioactivity in freshwater ecosystems, radionuclides of uranium and thorium series were measured in water, sediments, suspended matter, and fish samples from the rivers Vouga, D?o, Távora and Mondego. The results show that these rivers carry sediments with relatively high naturally occurring radioactivity, and display relatively high concentrations of radon dissolved in water, which is typical of a uranium rich region. Riverbed sediments show enhanced concentrations of radionuclides in the mid-section of the Mondego River, a sign of past wastewater discharges from mining and milling works at Urgeiri?a confirmed by the enhanced values of (238)U/(232)Th radionuclide ratios in sediments. Radionuclide concentrations in water, suspended matter and freshwater fish from that section of Mondego are also enhanced in comparison with concentrations measured in other rivers. Based on current radionuclide concentrations in fish, regular consumption of freshwater species by local populations would add 0.032 mSv a(-1) of dose equivalent (1%) to the average background radiation dose. Therefore, it is concluded that current levels of enhanced radioactivity do not pose a significant radiological risk either to aquatic fauna or to freshwater fish consumers.     

An estimation of radiation doses to benthic invertebrates from sediments collected near a Canadian uranium mine.

A new method is described for calculating radiation doses to benthic invertebrates from radionuclide concentrations in freshwater sediment. Both internal and external radiation doses were estimated for all 14 principal radionuclides of the uranium-238 decay series. Sediments were collected from three sites downstream of a uranium mining operation in northern Saskatchewan, Canada. Sediments from two sites, located approximately 1.6 and 4.4 km downstream from mining operations, yielded absorbed doses to both larval midges, Chironomus tentans, and adult amphipods, Hyalella azteca, of 59-60 and 19 mGy/year, respectively, compared to 3.2 mGy/year for a nearby control site. External beta radiation from protactinium-234 (234Pa) and alpha radiation from uranium (U) contributed most of the dose at the impacted sites, whereas polonium-210 (210Po) was most important at the control site. If a weighting factor of 20 was employed for the greater biological effect of alpha vs. beta and gamma radiation, then total equivalent doses rose to 540-560 mGy/year at the site closest to uranium operations. Such equivalent doses are above the 360-mGy/year no-observed-effect level for reproductive effects in vertebrates from gamma radiation exposure. Data are not available to determine the effect of such doses on benthic organisms, but they are high enough to warrant concern. Detrimental effects have been observed in H. azteca at similar uranium concentration in laboratory toxicity tests, but it remains unclear whether the radiotoxicity or the chemotoxicity of uranium is responsible for these effects.     

Assessment of the radiological impacts of historical coal mining operations on the environment of Ny-Alesund, Svalbard

Mineral extraction activities, such as those conducted by oil, gas and coal industries, are widespread throughout the Arctic region. Waste products of these activities can result in significant contributions to the radioactive burden of the surrounding environment due to increased concentrations of naturally occurring radioactive materials (NORM) to levels that would not normally be found in the environment. Coal mining operations commenced in the early 1900s on Svalbard and have been conducted at a variety of locations on the archipelago since then. Coal contains radionuclides of the uranium and thorium series as well as 40K. Extraction and processing of coal can result in releases of these radionuclides to the broader environment with subsequent impact on the human and non-human inhabitants of the area. This paper presents the results of a study on environmental radioactivity resulting from historical coal mining operations conducted at Ny-Alesund, Spitsbergen, in the Svalbard archipelago. Activity concentrations of radionuclides found in materials associated with these operations are presented as well as the results of a spatial dosimetric survey conducted over an area affected by coal mining.     

Nuclide migration and the environmental radiochemistry of Florida phosphogypsum

Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents one of the most serious problems facing the phosphate industry in Florida today. This by-product gypsum precipitates during the reaction of sulfuric acid with phosphate rock and is stored at a rate of about 40 million tons per year on several stacks in central and northern Florida. The main problem associated with this material concerns the relatively high levels of natural uranium-series radionuclides and other impurities which could have an impact on the environment and prevent its commercial use. We have studied the potential release of radionuclides from phosphogypsum by: (i) analysis of stack fluids, groundwaters, and soils associated with gypsum stacks; and (ii) geochemical modeling. Stack fluids were observed to be very high in dissolved uranium and 210Pb with only moderate concentrations of 226Ra. Underlying soils tend to be enriched in U and 210Pb indicating precipitation when acidic stack fluids enter a buffered environment. Modeling results showed significant increases in radionuclide complexes with sulfate and phosphate, resulting in relatively mobile uncharged or negatively charged solution species within the stacks with likely precipitation of multicomponent solids with increasing pH below the stack. Our evidence thus suggests that, while phosphogypsum stacks do contain significant quantities of dissolved radionuclides, removal mechanisms appear to prevent large-scale migration of radionuclides to the underlying aquifer.     

Radionuclide content of building materials and associated gamma dose rates in Egyptian dwellings

Studies have been carried out to determine the natural radioactivity in some building materials (bricks, tiles, marble and ceramics) and their associated radiation hazard. The radioactivity concentrations of ²²⁶Ra ²³²Th and ⁴⁰K were measured using a gamma spectrometer with a Hp–Ge detector. The activities of ²³⁸U and ²³⁴U were measured using an alpha-spectrometer with a surface barrier detector after applying a radiochemical procedure. The ²³⁴U/²³⁸U isotopic ratios were calculated. The radium equivalent activities and the radiation hazard index associated with the natural radionuclides were calculated. A computer program was developed and applied to calculate the dose rate a person will receive from the walls of a room constructed from the studied building materials.     

Radioecology in the vicinity of prospected uranium mining sites in a subarctic environment

A radioecological investigation has been carried out in two uranium-rich areas in northern Sweden. Aquatic, terrestrial and atmospheric samples have been analysed, mainly for radionuclides in the uranium series. In one of the areas, about ten times higher concentrations of uranium, thorium and radium were found in lichen close to the mineralization, due to aerial dispersion. In the aquatic system, no signs of enhanced levels were observed. For the short-lived radon daughters in air, there was no correlation between concentrations and distance from mineralization, as a result of the high natural background.     

Natural radioactivity, dose assessment and uranium uptake by agricultural crops at Khan Al-Zabeeb, Jordan

Khan Al-Zabeeb, an irrigated cultivated area lies above a superficial uranium deposits, is regularly used to produce vegetables and fruits consumed by the public. Both soil and plant samples collected from the study area were investigated for their natural radioactivity to determine the uranium uptake by crops and hence to estimate the effective dose equivalent to human consumption. Concentrations of (238)U, (235)U, (232)Th, (226)Ra, (222)Rn, (137)Cs and (40)K in nine soil profiles were measured by gamma-ray spectrometry whereas watermelon and zucchini crops were analyzed for their uranium content by means of alpha spectrometry after radiochemical separation. Correlations between measured radionuclides were made and their activity ratios were determined to evaluate their geochemical behavior in the soil profiles. Calculated soil-plant transfer factors indicate that the green parts (leaves, stems and roots) of the studied crops tend to accumulate uranium about two orders of magnitude higher than the fruits. The maximum dose from ingestion of 1 kg of watermelon pulp was estimated to be 3.1 and 4.7 nSv y(-1) for (238)U and (234)U, respectively. Estimations of the annual effective dose equivalent due to external exposure showed extremely low values. Radium equivalent activity and external hazard index were seen to exceed the permissible limits of 370 Bq kg(-1) and 1, respectively.     

Intake of uranium and radium-226 due to food crops consumption in the phosphate region of Pernambuco--Brazil

The phosphate region located in the Northeast of Brazil covers an area of approximately 150 km long with an average width of 4 km, along the coast of the states of Pernambuco and Paraíba. The inhabitants of this area are exposed to natural radioactivity levels higher than the background values recorded in the literature, mainly due to the presence of uranium and its decay products in the phosphatic sediments. The main aim of this study was to determine the activity concentration of uranium and (226)Ra in foodstuffs cultivated in this area, where the phosphate mineral has been extracted. The activity concentrations found for uranium and (226)Ra in the foodstuffs analyzed varied from 13 to 186 mBq kg(-1) (wet weight), with a mean value of 46 mBq kg(-1) and from 43 to 2209 mBq kg(-1) (wet weight), with a mean value of 358 mBq kg(-1), respectively. The annual intake of these radionuclides, for rural residents, was 7.45 Bq for uranium and 69.3 Bq for (226)Ra.     

Fractionation of natural radionuclides in soils from a uranium mineralized area in the south-west of Spain

A new version of a classical method was applied to study the distribution of natural radionuclides (238U, 230Th, and 226Ra) in the soil fractions obtained by a sequential extraction procedure. The potential significance of the fractions obtained with this method was tested on two very similar soils but with very different contents of the three radionuclides, collected in the proximity of a disused uranium mine located in the Extremadura region in the south-west of Spain. The results confirmed that, if only non-residual fractions are considered, the sequential method applied shows a characteristic speciation pattern of these natural radionuclides in this soil matrix, i.e., the distribution of each of the three radionuclides was very similar for the two soil samples.     

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.     

On monitoring anthropogenic airborne uranium concentrations and (235)U/(238)U isotopic ratio by Lichen - bio-indicator technique

Lichens are widely used to assess the atmospheric pollution by heavy metals and radionuclides. However, few studies are available in publications on using lichens to qualitatively assess the atmospheric pollution levels. The paper presents research results applying epiphytic lichens as bio-monitors of quantitative atmospheric contamination with uranium. The observations were conducted during 2.5 years in the natural environment. Two experimental sites were used: one in the vicinity of a uranium contamination source, the other one - at a sufficient distance away to represent the background conditions. Air and lichens were sampled at both sites monthly. Epiphytic lichens Hypogimnia physodes were used as bio-indicators. Lichen samples were taken from various trees at about 1.5m from the ground. Air was sampled with filters at sampling stations. The uranium content in lichen and air samples as well as isotopic mass ratios (235)U/(238)U were measured by mass-spectrometer technique after uranium pre-extraction. Measured content of uranium were 1.45 mgkg(-1) in lichen at 2.09 E-04 microgm(-3) in air and 0.106 mgkg(-1) in lichen at 1.13 E-05 microgm(-3) in air. The relationship of the uranium content in atmosphere and that in lichens was determined, C(AIR)=exp(1.1 x C(LICHEN)-12). The possibility of separate identification of natural and man-made uranium in lichens was demonstrated in principle.     

Fractionation of natural radionuclides in soils from the vicinity of a former uranium mine ?irovski vrh, Slovenia

As a result of former uranium mining and milling activities at ?irovski vrh, Slovenia, 0.6 million tons of uranium mill tailings (UMT) were deposited onto a nearby waste pile Boršt. Resulting enhanced levels of natural radionuclides in UMT could pose threat for the surrounding environment. Therefore, sequential extraction protocol was performed to assess mobility and bioavailability of ²³⁸U, ²³⁴U, ²³⁰Th and ²²⁶Ra in soils from the waste pile and its surrounding. The radionuclides associated with exchangeable, organic, carbonate, Fe/Mn oxides and residual fraction, respectively, were determined. Results showed that the highest activity concentrations for the studied radionuclides were on the bottom of the waste pile. In non-contaminated locations, about 80% of all radionuclides were in the residual fraction. Considering activity concentrations in the UMT, ²³⁸U and ²³⁴U are the most mobile. Mobility of ²²⁶Ra is suppressed by high sulphate concentrations and is similar to mobility of ²³⁰Th.     

Assessment of natural radiation exposure and radon exhalation from building materials in Greece

In controlling the natural radiation exposure for the residents of dwellings, it is necessary to determine the levels of natural radioactivity (external exposure) and radon exhalation rate (internal exposure) from building materials. Using a high-resolution gamma ray spectrometry system, the activity concentration of natural radionuclides was measured. The radon exhalation rate was measured by hermetically closing the sample in a container and following the radon activity growth as a function of time. Three different methods were applied in order to find the most appropriate, i.e. that with the less uncertainty for the less exposure time. Typical building materials were analyzed in order to examine the external and internal exposures. In addition, the total annual effective dose was evaluated for the residents of a typical Greek dwelling.     

Present status of 222Rn in groundwater in Extremadura

Radon-222 was measured in groundwater sources of Extremadura (Spain), analyzing 350 samples from private and public springs, wells, and spas by liquid scintillation counting (LSC) and gamma spectrometry. The (222)Rn activity concentrations ranged from 0.24 to 1168BqL(-1). The statistical analysis showed a log-normal distribution with a mean of (111+/-7)BqL(-1) and a median of (36+/-3)BqL(-1). A hydrogeological study revealed correlations between the activity concentration and the aquifer material's characteristics. A map of (222)Rn in groundwater was elaborated and compared with the natural gamma radiation map for this region. About 35% of the samples showed (222)Rn activity concentrations above the Euratom recommended limit of 100BqL(-1). Three uranium series radionuclides ((238)U, (234)U, and (226)Ra) were also assayed by alpha-particle spectrometry, estimating the annual effective dose due to the presence of these natural radionuclides in drinking water.     

Spatial distribution of natural radioactivity levels in topsoil around the high-uranium mineralization zone of Kylleng-Pyndensohiong (Mawthabah) areas, West Khasi Hills District, Meghalaya, India

A study of background radiation and the distribution of radionuclides in the environment of the proposed uranium mining sites of Kylleng-Pyndensohiong (Mawthabah) areas, West Khasi Hills District, Meghalaya, India, has been carried out with the objective of establishing a baseline radiation level of the region. Topsoil samples collected from the region are analysed for radioactivity measurements of primordial radionuclides by gamma-spectrometry technique. Direct dose measurement using a survey meter was also carried out simultaneously. Measurement carried out in the region shows that the activity concentration of (238)U and (232)Th in soil samples is found to be highest in Kylleng with respective median values of 335.3Bqkg(-1) and 283.9Bqkg(-1) followed by Syngkai with activity concentration of 285.3Bqkg(-1) and 257.4Bqkg(-1) for (238)U and (232)Th, respectively. The distribution of (40)K concentration in the study area is found to be in the range of 173.1-359.0Bqkg(-1) which is below the global and Indian average values of 420Bqkg(-1) and 394Bqkg(-1), respectively. The contribution of the primordial radionuclides to the total dose of the study area is found to be very high with a range of 136.8-334.5nGyh(-1) in comparison to the global as well as Indian average values.     

Uptake of uranium and thorium by native and cultivated plants

Large part of available literature on biogeochemistry of uranium and thorium refers to the studies performed either in highly contaminated areas or in nutrient solutions that have been artificially ‘spiked’ with radionuclides. Effects of background levels of natural radioactivity on soil-grown plants have not been studied to the same extent. In this paper, we summarised results of greenhouse and field experiments performed by the author from 2000 to 2006. We examined some of the factors affecting transfer of U and Th from soil to plants, differences in uptake of these radionuclides by different plants, relationships between U and Th in soil and in plants, and temporal variations of U and Th in different plant species. Concentrations of radionuclides (critical point for experimental studies on biogeochemistry of U and Th - rare trace elements in non-contaminated regions) and essential plant nutrients and trace elements were determined by instrumental neutron activation analysis.