Soil radium, soil gas radon and indoor radon empirical relationships to assist in post-closure impact assessment related to near-surface radioactive waste disposal

Least squares (LS), Theil’s (TS) and weighted total least squares (WTLS) regression analysis methods are used to develop empirical relationships between radium in the ground, radon in soil and radon in dwellings to assist in the post-closure assessment of indoor radon related to near-surface radioactive waste disposal at the Low Level Waste Repository in England. The data sets used are (i) estimated ²²⁶Ra in the <2 mm fraction of topsoils (eRa226) derived from equivalent uranium (eU) from airborne gamma spectrometry data, (ii) eRa226 derived from measurements of uranium in soil geochemical samples, (iii) soil gas radon and (iv) indoor radon data. For models comparing indoor radon and (i) eRa226 derived from airborne eU data and (ii) soil gas radon data, some of the geological groupings have significant slopes. For these groupings there is reasonable agreement in slope and intercept between the three regression analysis methods (LS, TS and WTLS). Relationships between radon in dwellings and radium in the ground or radon in soil differ depending on the characteristics of the underlying geological units, with more permeable units having steeper slopes and higher indoor radon concentrations for a given radium or soil gas radon concentration in the ground. The regression models comparing indoor radon with soil gas radon have intercepts close to 5 Bq m⁻³ whilst the intercepts for those comparing indoor radon with eRa226 from airborne eU vary from about 20 Bq m⁻³ for a moderately permeable geological unit to about 40 Bq m⁻³ for highly permeable limestone, implying unrealistically high contributions to indoor radon from sources other than the ground. An intercept value of 5 Bq m⁻³ is assumed as an appropriate mean value for the UK for sources of indoor radon other than radon from the ground, based on examination of UK data. Comparison with published data used to derive an average indoor radon: soil ²²⁶Ra ratio shows that whereas the published data are generally clustered with no obvious correlation, the data from this study have substantially different relationships depending largely on the permeability of the underlying geology. Models for the relatively impermeable geological units plot parallel to the average indoor radon: soil ²²⁶Ra model but with lower indoor radon: soil ²²⁶Ra ratios, whilst the models for the permeable geological units plot parallel to the average indoor radon: soil ²²⁶Ra model but with higher than average indoor radon: soil ²²⁶Ra ratios.     

High natural radiation exposure in radon spa areas: a detailed field investigation in Niska Banja (Balkan region)

The measurement campaigns have been done in the rural community of Niska Banja, a spa town located in southern Serbia, to evaluate population exposure to natural radioactivity. After a screening survey in 200 houses, annual radon and thoron concentrations were measured in 34 houses, and in 2004 a detailed investigation was carried out at six houses with elevated indoor radon concentrations. The paper presents the results of these detailed measurements. The complementary techniques were applied to determine radon and thoron concentrations in indoor air, in soil gas, radon exhalation from soil, soil permeability, and indoor and outdoor gamma doses. Soil and water samples were collected and analysed in the laboratory. Indoor radon and thoron concentrations were found to be more than 1kBqm(-3) and 200Bqm(-3), respectively. Extremely high concentrations of soil-gas radon (>2000kBqm(-3)) and radon exhalation rates (1.5mBqm(-2)s(-1)) were observed. These results will be utilised to set up the methodology for a more systematic investigation.     

Natural radiation exposure in the Campo Arañuelo region in the surroundings of Almaraz nuclear power station (Spain)

During 1998 regional surveys were conducted to evaluate natural radiation exposure of people in the vicinity of the six Spanish nuclear power stations. Indoor radon, external gamma dose rates outdoors and indoors and radioactivity in soil were measured in these surveys. The highest mean annual effective dose to the population was found in the surroundings of the Almaraz nuclear power plant in the province of Cáceres and was mainly due to the presence of high radon concentrations in homes. In order to make a more accurate assessment of the dose coming from the radon in this area, a new and more extensive surgery on indoor radon with a total of 380 measurements was carried out in 2000 in the Campo Ara?uelo region around the Almaraz nuclear power station. From the results obtained in this survey, a population-weighted mean annual effective dose from radon exposure of 1.7 mSv y(-1), 44% lower than that previously reported in 1998, was estimated for the whole Campo Ara?uelo region. The maximum dose value due to radon exposure, about 4 mSv y(-1), was reached in the so-called La Vera area located in the north of this region. The relationship between the indoor radon concentrates experimentally measured, the geological characteristics of this geographic area and the information provided by the radiation map of the Spanish MARNA Project is also analyzed, confirming that La Vera area should be considered as a high radon level area.     

Radon survey in the high natural radiation region of Niska Banja, Serbia

A radon survey has been carried out around the town of Niska Banja (Serbia) in a region partly located over travertine formations, showing an enhanced level of natural radioactivity. Outdoor and indoor radon concentrations were measured seasonally over the whole year, using CR-39 diffusion type radon detectors. Outdoor measurements were performed at 56 points distributed over both travertine and alluvium sediment formations. Indoor radon concentrations were measured in 102 living rooms and bedrooms of 65 family houses. In about 50% of all measurement sites, radon concentration was measured over each season separately, making it possible to estimate seasonal variations, which were then used to correct values measured over different periods, and to estimate annual values. The average annual indoor radon concentration was estimated at over 1500 Bq/m3 and at about 650 Bq/m3 in parts of Niska Banja located over travertine and alluvium sediment formations, respectively, with maximum values exceeding 6000 Bq/m3. The average value of outdoor annual radon concentration was 57 Bq/m3, with a maximum value of 168 Bq/m3. The high values of indoor and outdoor radon concentrations found at Niska Banja make this region a high natural background radiation area. Statistical analysis of our data confirms that the level of indoor radon concentration depends primarily on the underlying soil and building characteristics.     

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).     

Natural radioactivity in some major rivers of coastal Karnataka on the southwest coast of India

Systematic studies on radiation level and distribution of radionuclides have been carried out in riverine environs of three major rivers of coastal Karnataka, viz. Kali, Sharavathi and Netravathi. The ambient gamma radiation levels along three rivers were measured using a portable plastic scintillometer. Activity concentrations of (226)Ra, (232)Th and (40)K in soil, sediment and rock were measured using a NaI(Tl) gamma-ray spectrometer. In the Kali, Sharavathi and Netravathi riverbanks, the median values of absorbed gamma dose rates in air were found to be 44 nGy h(-1), 35 nGy h(-1) and 57 nGy h(-1), respectively. The highest activity of (226)Ra was found in riverbank soil samples of Sharavathi River. The highest activities of (232)Th and (40)K were found in riverbank soil and sediment samples of Netravathi River. In Kali River, the highest (226)Ra activity was recorded for rock samples. To assess the radiological hazard of natural radioactivity in the samples, absorbed gamma dose rates in air, radium equivalent activity, representative level index, external hazard index and internal hazard index associated with the radionuclides were calculated and compared with internationally recommended values. The representative level index (I(gammar)) values are high in sediment samples of Netravathi River. The radium equivalent activity (Ra(eq)), external hazard index (H(ex)) and internal hazard index (H(in)) values are high in rock samples of Kali River. The results of these investigations are presented and discussed in this paper.     

Indoor air quality: Radon—Report on a WHO working group

The WHO Regional Office for Europe organized a working group in Dubrovnik, Yugoslavia, on 26–30 August 1985, which discussed radon as a pollutant affecting indoor air quality. Much of the natural background radiation to which the general public is exposed comes from the decay of ²²⁶Ra which produces radon gas and other products. Because radium is a trace element in most rock and soil, indoor concentrations of radon can come from a wide variety of substances, such as building materials and the soil under building foundations. Tap water taken from wells or underground springs may be an additional source. Radon daughter concentrations are considerably higher indoors than outdoors and are of the order of 2–5 Bq m⁻³ equilibrium equivalent radon (EER) concentration. It has been estimated that current exposure to radon gas could account for as much as 5–15% of all lung cancer deaths. It was recommended that, in general, buildings with concentrations of more than 100 Bq m⁻³ EER, as an annual average, should be considered for remedial action to lower such concentrations if simple measures are possible.     

Indoor gamma radiation and radon concentrations in a Norwegian carbonatite area

Results of indoor gamma radiation and radon measurements in 95 wooden dwellings located in a Norwegian thorium-rich carbonatite area using thermoluminescent dosemeters and CR-39 alpha track detectors, respectively, are reported together with a thorough analysis of the indoor data with regard to geological factors. Slightly enhanced radium levels and thorium concentrations of several thousands Bq kg(-1) in the carbonatites were found to cause elevated indoor radon-222 levels and the highest indoor gamma dose rates ever reported from wooden houses in Norway. An arithmetic mean indoor gamma dose rate of 200 nGy h(-1) and a maximum of 620 nGy h(-1) were obtained for the group of dwellings located directly on the most thorium-rich bedrock.     

Determination of indoor radon and soil radioactivity levels in Giresun, Turkey

Indoor radon survey and gamma activity measurements in soil samples were carried out in the Giresun province (Northeastern Turkey). The result of analysis of variance showed a relationship between indoor radon and radium content in soil (R(2)=0.54). It was found that indoor radon activity concentration ranged from 52 to 360 Bq m(-3) with an average value of 130 Bq m(-3). A model built by BEIR VI was used to predict the number of lung cancer deaths due to indoor radon exposure. It was found that indoor radon is responsible for 8% of all lung cancer deaths occurring in this province. (137)Cs activity concentration was measured 21 years after the Chernobyl accident. The results showed that (137)Cs activity concentration ranged from 41 to 1304 Bq kg(-1) with an average value of 307 Bq kg(-1). The indoor radon results and the geology of the studied area were discussed. Annual effective doses to the both radionuclides of natural origin and (137)Cs were estimated.     

Comparative studies of health hazard from radon (Rn-222) in two selected lithologic formations in the Suwałki region (in Poland)

The aim of this work was to make a comparison of indoor radon concentrations in dwellings and in soil air in the area of two geological formations in the Suwa?ki region (Poland). The mean arithmetic airborne concentration was found to be the highest (301 Bq m (-3)) in the basements of buildings in the gravel and sand areas, whereas in the boulder clay areas it reached 587 Bq m (-3). Out of 54 measurements of radon concentrations performed at the ground floor, in eight cases concentrations were found to exceed 200 Bq m (-3) - permissible radon level in new-built houses in Poland and in three cases these values were even higher than 400 Bq m (-3). The highest radon levels were noted in houses with earthen basement floors and with direct entrance from the basement to rooms or kitchens. The mean arithmetic radon concentration in the soil air in the sandy and gravel formations was 39.7 kBq m (-3) and in clay formation it was 26.5 kBq m (-3). Higher radon levels were also found in the water obtained from household wells reaching 8367 Bq m (-3) as compared with tap water (2690 Bqm (-3)). The mean indoor concentration for the whole area under study was found to be 169.4 Bq m (-3), which is higher than the mean value for Poland (49.1 Bq m (-3)) by a factor of 3.5.     

Pilot study of the application of Tellus airborne radiometric and soil geochemical data for radon mapping

The scope for using Tellus Project airborne gamma-ray spectrometer and soil geochemical data to predict the probability of houses in Northern Ireland having high indoor radon concentrations is evaluated, in a pilot study in the southeast of the province, by comparing these data statistically with in-house radon measurements. There is generally good agreement between radon maps modelled from the airborne radiometric and soil geochemical data using multivariate linear regression analysis and conventional radon maps which depend solely on geological and indoor radon data. The radon maps based on the Tellus Project data identify some additional areas where the radon risk appears to be relatively high compared with the conventional radon maps. One of the ways of validating radon maps modelled on the Tellus Project data will be to carry out additional indoor measurements in these areas.     

Radon concentrations in a spa in Serbia

The paper presents the results of indoor radon concentration survey in 201 homes and offices in Niska Banja (the Spa of Nis), a well-known health resort and a spa in the South-East of Serbia. Radon indoor concentrations were determined by active charcoal method, according to standard EPA procedure. The indoor radon concentrations were in the range of up to 200 Bq/m(3) (47%), from 200-600 Bq/m(3) (26%) and over 600 Bq/m(3) (27%). Three areas of extremely high average radon concentrations were found (1,340-4,340 Bq/m(3)), with a maximum above 13,000 Bq/m(3). The content of natural radionuclides ((226)Ra, (214)Pb, (214)Bi, (235)U, (228)Ac, (212)Pb, (212)Bi, (208)Tl, (40)K) and (137)Cs, as well as the content of total uranium, thorium and potassium in mud used in peloidotherapy in the Health Institute "Niska Banja" was determined, too. The activities of the radionuclides were determined on an HPGe detector, by standard gamma spectroscopy. The results indicated considerably high amounts of total uranium and thorium (0.021 g/kg mud and 0.003 g/kg mud, respectively), due to the karsts origin of the soil.     

Radon and thoron monitoring in the environment of Kumaun Himalayas: survey and outcomes

Monitoring of radon, thoron and their daughter products was carried out in houses of Kumaun Himalaya, India using LR-115 plastic track detectors. The measurements were made in residential houses from June 1999 to May 2000 at a height of 2.5 m from ground level using a twin chamber radon dosimeter. The twin chamber radon dosimeter can record the values of radon, thoron and their decay products separately. Maximum and minimum indoor radon and thoron concentrations were evaluated and activity concentrations of radon and thoron daughters were estimated. The resulting dose rates due to radon, thoron and their decay products varied from 0.04 to 1.89 microSv/h. A detailed analysis of the distribution of radon, thoron and their decay products inside the house is also reported. The observed dose rates inside the houses of Kumaun Himalaya were found to be lower than the ICRP recommended value of 200 Bq/m3 and thus are within safe limits.     

Uranium-238 and thorium-232 series concentrations in soil, radon-222 indoor and drinking water concentrations and dose assessment in the city of Aldama, Chihuahua, Mexico

High-resolution gamma spectrometry was used to determine the concentration of 40K, 238U and 232Th series in soil samples taken from areas surrounding the city of Aldama, in Chihuahua. Results of indoor air short-time sampling, with diffusion barrier charcoal detectors, revealed relatively high indoor radon levels, ranging from 29 to 422 Bq/m3; the radon concentrations detected exceeded 148 Bq/m3 in 76% of the homes tested. Additionally, liquid scintillation counting showed concentrations of radon in drinking water ranging from 4.3 to 42 kBq/m3. The high activity of 238U in soil found in some places may be a result of the uranium milling process performed 20 years ago in the area. High radon concentrations indoor and in water may be explained by assuming the presence of uranium-bearing rocks underneath of the city, similar to a felsic dike located near Aldama. The estimated annual effective dose of gamma radiation from the soil and radon inhalation was 3.83 mSv.     

Radioecological characterization of a uranium mining site located in a semi-arid region in Brazil

The work presents the radioecological characterization of the new Brazilian uranium mining and milling site located in a semi-arid region of the country. The process characterization demonstrated that in heap leach plants most of the 226Ra remains in the leached ore. Despite the potential higher availability of radium isotopes in the soils of the studied region the lack of precipitation in that area reduces the leaching/mobilization of the radionuclides. High 226Ra and 228Ra concentrations were found in manioc while 210Pb was significant in pasture. It was suggested that a range from 10(-3) to 10(-1) may conveniently encompass most of the transfer factors (TF) values for soil/plant systems (i.e. involving different cultures, different soils and natural radionuclides). Impacts due to aerial transportation of aerosols and radon generated in the mining were proved to be minimal and restricted to an area not greater than 15 km2. Finally, uranium complexation by carbonates was shown to be the main mechanism responding for the elevated radionuclide concentration in groundwater.     

Preliminary indoor radon risk assessment at the Poços de Caldas Plateau,MG-Brazil

This paper aims to present an assessment of the environmental radiological exposure at a Brazilian area of high natural radiation and discusses the indoor radon exposure risk. A survey of inhabitant exposures arising from the inhalation of radon progeny and external gamma exposure was conducted in urban and rural areas of the Po?os de Caldas Plateau, which is recognized worldwide as a high natural radiation region. The results of this survey indicated that highest radiation exposure was restricted to the rural area of Po?os de Caldas. The radiation exposure in urban locations was quite similar to the values observed in normal background areas in some Brazilian counties. By the application of a constant relative risk model, an additional 20% in the lifetime risk of lung cancer mortality due to the exposure to radon progeny was estimated at Po?os de Caldas. It was also estimated that 16% of all lung cancer deaths at Po?os de Caldas county could be attributable to radon exposure.     

First steps towards a European atlas of natural radiation: status of the European indoor radon map

Within the context of its institutional scientific support to the European Commission, in 2005 the Radioactivity Environmental Monitoring (REM) group at the Joint Research Centre of the European Commission, started to explore the possibility of mapping indoor radon in European houses as a first step towards preparing a European Atlas of Natural Radiations. The main objective of such an atlas is to contribute to familiarizing the public with its naturally radioactive environment. The process of preparing the atlas should also provide the scientific community with a database of information that can be used for further studies and for highlighting regions with elevated levels of natural radiation. This document presents the status of the European indoor radon (Rn) map, first statistical results, and outlines of forthcoming challenges.     

226Ra concentration in the teeth of habitants of areas with high level of natural radioactivity in Ramsar

The level of natural radiation in some regions of Ramsar, a northern coastal city of Iran, is known to be among the highest levels of natural radiation in the world. 226Ra existing in high concentrations in the soil of this region is washed by underground water and transferred to the surface. In this way, 226Ra enters the food chain of residents and substitutes within the hard body tissues of humans. 226Ra is one of the so-called bone seekers as its metabolic processes in the human body are similar to calcium and remains in hard tissues of body because of its long half-life, and being an alpha emitter causes dangerous effects on human health. The purpose of this study is to determine the concentration of 226Ra in the teeth of residents of these high-level natural radiation areas, compared with a control group. Thirteen teeth in five groups were studied as the case group and thirteen teeth in five corresponding control groups were inspected. The mean values of the activity of 226Ra in the case group and in the control group were 0.32 and 0.18mBqg(-1), respectively.     

Estimating the amount and distribution of radon flux density from the soil surface in China

Based on an idealized model, both the annual and the seasonal radon ((222)Rn) flux densities from the soil surface at 1099 sites in China were estimated by linking a database of soil (226)Ra content and a global ecosystems database. Digital maps of the (222)Rn flux density in China were constructed in a spatial resolution of 25 km x 25 km by interpolation among the estimated data. An area-weighted annual average (222)Rn flux density from the soil surface across China was estimated to be 29.7+/-9.4 mBq m(-2)s(-1). Both regional and seasonal variations in the (222)Rn flux densities are significant in China. Annual average flux densities in the southeastern and northwestern China are generally higher than those in other regions of China, because of high soil (226)Ra content in the southeastern area and high soil aridity in the northwestern one. The seasonal average flux density is generally higher in summer/spring than winter, since relatively higher soil temperature and lower soil water saturation in summer/spring than other seasons are common in China.     

Radon-222 exhalation from open ground on and around a uranium mine in the wet-dry tropics

Radon-222 exhalation from the ground surface depends upon a number of variables such as the 226Ra activity concentration and its distribution in soil grains; soil grain size; soil porosity, temperature and moisture; atmospheric pressure, rainfall and temperature. In this study, 222Rn exhalation flux density measurements within and around the Ranger uranium mine in northern Australia were performed to investigate the effect of these variables within a tropical region. Measurements were taken at the waste rock dumps, ore stockpiles, mine pits, and at sites where effluent water with elevated 226Ra concentration has been spray irrigated over land, as well as at sites outside the mine. The sites selected represented a variety of geomorphic regions ranging from uranium-bearing rocks to ambient soils. Generally, wet season rains reduced 222Rn exhalation but at a few sites the onset of rains caused a step rise in exhalation flux densities. The results show that parameters such as 226Ra activity concentration, soil grain size and soil porosity have a marked effect on 222Rn flux densities. For similar geomorphic sites, 226Ra activity concentration is a dominant factor, but soil grain size and porosity also influence 222Rn exhalation. Surfaces with vegetation showed higher exhalation flux densities than their barren counterparts, perhaps because the associated root structure increases soil porosity and moisture retention. Repeated measurements over one year at eight sites enabled an analysis of precipitation and soil moisture effects on 222Rn exhalation. Soil moisture depth profiles varied both between seasons and at different times during the wet season, indicating that factors such as duration, intensity and time between precipitation events can influence 222Rn flux densities considerably.