Thorium Series Radionuclides Research Articles

A comparative study of the elevated radioactivity in beach placer deposits of Bangladesh.

Beach sediments are mineral deposits formed through weathering and erosion of either igneous or metamorphic rocks. Among the rock constituent minerals are some natural radionuclides that contribute to ionizing radiation exposure on Earth. Kolatoli and Kuakata are the two major beaches with heavy mineral deposits and important tourist sites in Bangladesh. Natural radioactivity in Kolatoli and Kuakata beach sand deposits along the southern coast of Bangladesh was assessed and compared to identify the sources, causes, and possible environmental impact. Result shows most of the radionuclides have higher activity concentrations than the background level, and the activity varies with the sample locations. The dominant radionuclides were found to be the radionuclides of thorium series i.e. Th-232 and Ra-228 followed by uranium series and K-40. The radioactivity in Kolatoli beach sands was observed to be much higher than Kuakata beach due to the presence of a higher content of heavy minerals i.e. illmenite, rutile, zircon, garnet and monazite. Furthermore, monazite and zircon are the two radioactive minerals that are considered to be the main contributors to the radioactivity in Kolatoli beach sand. These minerals are dominated by the activity of thorium series radionuclides i.e. Th-232 and Ra-228 surpass the activity of all other radionuclides such as U-238, U-234, Th-230, Ra-226, Po-210, and K-40. However, major contribution of radioactivity in Kuakata beach sand comes from uranium series radionuclides such as U-238, U-234, Ra-226, and Po-210. Beach morphology, sedimentological, and geochemical evolution of those minerals might be important areas of further study for the radioactivity monitoring activity in those areas.

Radiological risk assessment of farm-raised fish species due to natural radionuclides in the freshwater ecosystem of Bangladesh with the statistical approach

We study radiation exposure resulting from the consumption of farm-raised freshwater fish species that form an essential part of the Bangladeshi diet. The levels of radioactivity in the human diet are of particular concern, requiring assessment of possible radiological risks to human health. Therefore, a comprehensive study was carried out to determine the radioactivity levels (226Ra, 228Ra, and 40K) in fifteen commonly available varieties of farm-raised fishes. The gamma-ray spectroscopic analysis showed the presence of radionuclides of 226Ra, 228Ra, and 40K in all studied fishes, but varying degrees. The highest radioactivity levels of 226Ra, 40K, and 228Ra were observed in Rui (Labeo rohita) and Tilapia (Oreochromis mossambicus) with values of 8.50 ± 0.30, 513.28 ± 1.59, and 7.41 ± 0.15 Bqkg−1, respectively. The respective radioactivity levels were lowest in Silver carp (Hypophthalmichthys molitrix), Mola (Amblypharyngodon mola), and Koi (Anabas testudineus) with values of 0.83 ± 0.38, 171.07 ± 1.60, and 0.62 ± 0.30 Bqkg−1. The doses for 226Ra, 228Ra, and 40K due to consumption of a kilogram of farm fish were assessed and range from 5.56 (Sarputi – Puntius sarana) to 54.36 µSvy–1 (Rui – Labeo rohita), 9.77 (Koi – A. testudineus) to 116.79 µSvy–1 (Tilapia – O. mossambicus), and 24.23 (Mola – A. mola) to 72.69 µSvy–1 (Rui – Labeo rohita), respectively. In most cases, the estimated probability of an increase of cancer risk from daily intake of the farm-raised fish diet representing a minor fraction of ICRP values. Statistical analysis shows that the radioactivity and estimated radiological parameters are strongly correlated with 226Ra and 228Ra, while weakly correlated to 40K, suggesting that radiological risk is basically associated and controlled by the activity levels of uranium and thorium series radionuclides.

Occurrence and behavior of uranium and thorium series radionuclides in the Permian shale hydraulic fracturing wastes.

Over the last decade, there has been a rapid growth in the use of hydraulic fracturing (fracking) to recover unconventional oil and gas in the Permian Basin of southeastern New Mexico (NM) and western Texas. Fracking generates enormous quantities of wastes that contain technologically enhanced naturally occurring radioactive materials (TENORM), which poses risks to human health and the environment because of the relatively high doses of radioactivity. However, very little is known about the chemical composition and radioactivity levels of Permian Basin fracking wastes. Here, we report chemical as well as radiochemical compositions of hydraulic fracking wastes from the Permian Basin. Radium, the major TENORM of interest in unconventional drilling wastes, varied from 19.1 ± 1.2 to 35.9 ± 3.2Bq/L for 226Ra, 10.3 ± 0.5 to 21.5 ± 1.2Bq/L for 228Ra, and 2.0 ± 0.05 to 3.7 ± 0.07Bq/L for 224Ra. In addition to elevated concentrations of radium, these wastewaters also contain elevated concentrations of dissolved salts and divalent cations such as Na+ (31,856-43,000mg/L), Ca2+ (668-4123mg/L), Mg2+ (202-2430mg/L), K+ (148-780mg/L), Sr2+ (101-260mg/L), Cl- (5160-66,700mg/L), SO42- (291-1980mg/L), Br- (315-596mg/L), SiO2 (20-32mg/L), and high total dissolved solid (TDS) of 5000-173,000mg/L compared to background waters. These elevated levels are of radiological significance and represent a major source of Ra in the environment. The recent discovery of large deposits of recoverable oil and gas in the Permian Basin will lead to more fracking, TENORM generation, and radium releases to the environment. This paper evaluates the potential radiation risks associated with TENORM wastes generated by the oil and gas recovery industry in the Permian Basin.

Evaluation of natural radionuclides distribution in beach sands of Cox’s bazar sea beach, Bangladesh, using multivariate statistical technique

ABSTRACT The distribution of natural series radionuclides 226Ra, 232Th and non-series 40K in the heavy mineral-rich beach sands of highly touristic areas of Cox’s Bazar sea beach has been studied. The study is made to evaluate the gamma radiation exposure to individuals with an aim to establish reference data for the presence of naturally occurring radionuclides. The present study reports the probable first attempt of detail and systematic work in the study areas for estimation of activity concentration in the recent beach sand samples. Radiometric analysis was performed using gamma ray spectroscopy system based on HPGe detector. The mean activity levels of 226Ra, 232Th and 40K in Laboni beach sands were ranged from 255.69±64.57, 336.83±93.96 and 1785.91±89.60 Bq kg-1, respectively. While in Kolatoli beach sands, the respective values were 166.42±35.99, 157.35±35.90 and 1894.42±74.07Bq kg-1, respectively. The mean values of 226Ra and 232Th concentrations in the investigated beach sands were estimated to be very much higher than the corresponding world average values and comparable to those found in high background radiation areas in the world. The heavy minerals seem to control the activity concentrations of 226Ra and 232Th in sand samples, showing some variances based on uranium and thorium bearing minerals. Various radiation health hazard indicators were found to be extremely higher when compared to the recommended values. Hence, heavy mineral-rich sands may pose a significant radiological health risk to the people. The descriptive statistics indicating the radionuclides of 226Ra, 232Th and 40K are uniformly and symmetrically distributed in the Cox’s bazar beach sand. Multivariate statistical analysis showing the radioactivity and estimated radiological parameters are strongly positively correlated with 226Ra and 232Th, while weakly correlated with 40K, signifying that radiological risk is mainly associated and controlled by the radioactivity levels of uranium and thorium series radionuclides.

Relationship Between Terrestrial Background and Remedial Criteria for Naturally Occurring Radioactive Material in the United States.

In the United States (US), Federal and State agencies have established radiological public exposure limits and remedial action ("clean up") criteria for naturally occurring radionuclides (NORM-primarily for uranium and thorium series radionuclides). Often, these criteria are intended to control human exposure to what is referred to in the US as technologically enhanced naturally occurring radioactive material (TENORM). This can be any naturally occurring radioactive material for which the potential for human exposure has been enhanced due to anthropogenic (human activities), e.g., removal from its "place in nature," and/or processed in some way resulting in concentration. In some cases, the values of these regulatory criteria can be similar to or even less than those levels of exposure and those concentrations of NORM that exists in nature independent of any previous human activity. The potential variability of NORM radionuclides in the soil and rocks can be significant, even over relatively short distances or depths due to factors such as geology, hydrology, and geochemistry. Given this, it is important to recognize that defining "the radiation background" for purposes of establishing and/or comparing remedial action criteria and/or exposure limits requires recognition of the specificity at the location(s) of interest, not in other geological and/or mineralogical regimes several miles away. The purpose of this paper is to demonstrate this variability for comparison to exposure levels and concentrations being defined in the US as levels above which require regulatory control and / or above which are being defined as an "unacceptable risk." The primary background exposure component of specific interest here is the annual dose contribution from terrestrial radiation exposure, i.e., from uranium and thorium series radionuclides in the ground, excluding radon inhalation. The exposure sources being controlled by some US regulatory limits are primarily associated with the primordial radionuclides in soil. The average annual terrestrial component of background can vary by upwards of a few tenths of a mSv across the US that can be several times higher than the applicable exposure limits. This can result in "unacceptable risk" or "remedial action" concentration criteria statistically equivalent to or less than the background concentrations of these same primordial nuclides. The statistical and analytical uncertainties of distinguishing naturally occurring radionuclides (i.e., NORM) from those resulting from anthropogenic (human caused) activities (i.e., TENORM) can be quite challenging and in some cases may be technically impossible. Consideration must be given to the relationship of the amount of actual total risk avoidance achieved if any, relative to the traditional health and safety risks of construction and associated construction and waste management costs for remedial activities, so that a practical and scientifically based approach for development of these criteria can be achieved.

Ingestion dose due to 226Ra, 228Ra, and 40K in the plant origin food materials grown around BARC, Visakhapatnam

Naturally occurring radionuclides of uranium, thorium series, and potassium are significant contributors of ingestion dose. Radioactive concentrations of 226Ra, 228Ra, and 40K in plant origin food cultivated around BARC, Visakhapatnam, were determined and the assessment of the ingestion dose through food consumption to different groups of population was estimated. Radionuclides in the samples analyzed were measured by high purity germanium gamma spectrometry system. The estimated annual effective dose from the ingestion of cereals, pulses, vegetables, fruits, and leafy vegetables due to 226Ra, 228Ra, and 40K radionuclides is 0.32 mSv. In this paper the estimated annual effective dose in the study area is compared to the ingestion dose due to intake of different food materials by various natural radionuclides reported in various parts of India and world. The data generated will be a useful baseline studies for the upcoming BARC facilities at Visakhapatnam, India.

Study of equilibrium status among uranium and thorium series radionuclides in soil samples from Visakhapatnam, India

Surface soil samples from coastal region of Visakhapatnam were analyzed for uranium series and thorium series radionuclides by high-resolution gamma-ray spectrometry. Isotopic ratios of 226Ra/238U and 224Ra/232Th were calculated to investigate the radioactive equilibrium status in the samples. 226Ra/238U and 224Ra/232Th ratios were found to vary from 0.80–1.40 to 0.94–1.40 with mean values of 1.05 and 0.99, respectively. Results showed a prevalent radioactive equilibrium for both uranium and thorium series radionuclides in the surface soil of the study area.

Quantitative autoradiography of alpha particle emission in geo-materials using the Beaver™ system

In rocks or artificial geo-materials, radioactive isotopes emitting alpha particles are dispersed according to the mineralogy. At hand specimen scale, the achievement of quantitative chemical mapping of these isotopes takes on a specific importance. Knowledge of the distribution of the uranium and thorium series radionuclides is of prime interest to several disciplines, from the geochemistry of uranium deposits, to the dispersion of uranium mill tailings in the biosphere. The disequilibrium of these disintegration chains is also commonly used for dating. However, some prime importance isotopes, such as 226Ra, are complicated to localize in geo-materials. Because of its high specific activity, 226Ra is found in very low concentrations (~ppq), preventing its accurate localization in rock forming minerals.This paper formulates a quantitative answer to the following question: at hand specimen scale, how can alpha emitters in geo-materials be mapped quantitatively? In this study, we tested a new digital autoradiographic method (called the Beaver™) based on a Micro Patterned Gaseous Detector (MPGD) in order to quantitatively map alpha emission at the centimeter scale rock section. Firstly, for two thin sections containing U-bearing minerals at secular equilibrium, we compared the experimental and theoretical alpha count rates, measured by the Beaver™ and calculated from the uranium content, respectively. We found that they are very similar. Secondly, for a set of eight homemade standards made up of a mixture of inactive sand and low-radioactivity mud, we compared the count rates obtained by the Beaver™ and by an alpha spectrometer. The results indicate (i) a linearity between both count rates, and (ii) that the count obtained by the Beaver™ can be estimated from the count obtained by the alpha spectrometry using a factor of 0.82.

Radioactive characterization of the main materials involved in the titanium dioxide production process and their environmental radiological impact

A study about the distribution of several radionuclides from the uranium and the thorium series radionuclides along the production process of a typical NORM industry devoted to the production of titanium dioxide has been performed. With this end the activity concentrations in raw materials, final product, co-products, and wastes of the production process have been determined by both gamma-ray and alpha-particle spectrometry.The main raw material used in the studied process (ilmenite) presents activity concentrations of around 300 Bq kg−1 for Th-series radionuclides and 100 Bq kg−1 for the U-series ones. These radionuclides in the industrial process are distributed in the different steps of the production process according mostly to the chemical behaviour of each radioelement, following different routes. As an example, most of the radium remains associated with the un-dissolved material waste, with activity concentrations around 3 kBq kg−1 of 228Ra and around 1 kBq kg−1 of 226Ra, while the final commercial products (TiO2 pigments and co-products) contain negligible amounts of radioactivity.The obtained results have allowed assessing the possible public radiological impact associated with the use of the products and co-products obtained in this type of industry, as well as the environmental radiological impact associated with the solid residues and liquid generated discharges.

Study on transfers of uranium, thorium and decay products from grain, water and soil to chicken meat and egg contents

Activity concentrations of the uranium and thorium series radionuclides were determined in chicken meat and eggs as well as in soil, water and other dietary intakes of poultry at five sites of the French territory. These data allow the calculation of transfer coefficients which enrich the database given by the technical report series no. 472 of the IAEA. In egg contents, the highest activity concentrations (in mBq kg(-1) fresh weight) are for (226)Ra, ranging between 136 and 190 and are much lower for uranium (between 0.51 and 1.30 for (238)U). In chicken meat, (238)U activity concentration is higher than in egg contents and ranges between 1.7 and 9.7. Concerning (232)Th, its activity concentration is lower than uranium and ranges between 0.5 and 4.9. Daily ingested activity concentration by the animals was assessed taking into account the activity concentrations measured in the grains, in the soil and in the drinking water. The activity concentration in grains and the daily intakes allow the calculation of concentration ratios and transfer coefficients for chicken meat and egg contents. In chicken meat the transfer coefficients (d kg(-1)) range between 0.0018 and 0.0073 for (238)U and between 0.0008 and 0.0028 for (232)Th. In egg contents they range from 0.00018 to 0.0018 for (238)U and are much higher for radium isotopes (0.10-0.23 for (226)Ra and 0.07-0.11 for (228)Ra).

Assessment of the reproductive capacity of Pinus sylvestris trees growing under conditions of chronic exposure to radionuclides of uranium and thorium series

The reproductive capacity of Scots pine (Pinus sylvestris L.) has been estimated in trees from the population growing in an area used to store tailings from uranium ore processing and radium production. Under such conditions, 12- to 15-year-old trees produce seeds of a quality inferior to that in areas with a normal background radiation level. As the weighted absorbed dose rate (at a weighting coefficient of 5) for generative organs increases from 0.002 ± 0.0003 to 0.344 ± 0.059 mGy/day, a proportional increase is observed in the proportion of empty seeds and the frequency of cytogenetic disturbances in the root meristem of seedlings, while the survival rate of seedlings decreases. The minimum absorbed dose rate leading to these changes in the pine population is 0.027 mGy/day, i.e., 12 times as high as the control value.

Thoron and decay products, beyond UNSCEAR 2006 Annex E

Uranium and thorium series radionuclides are present in all soils and rocks. Thus, radon and thoron, the radioactive noble gases originating in the uranium ((238)U) and thorium ((232)Th) decay chains is ubiquitous and everyone is exposed to both radon and thoron gases and their particulate radioactive decay products. As described in UNSCEAR Annex E (2006), radon and its decay products have been recognised for many years as a hazard to underground miners. More recently, the risks from exposure to residential radon have been demonstrated through residential case-control epidemiological studies. However, as discussed by UNSCEAR, exposures to thoron and its decay products have often been relatively ignored. Moreover, unlike radon the effects of exposure to thoron and its decay products are not available from epidemiology and thus, a dosimetric approach is required to assess risks. UNSCEAR continues to recommend the use of a dose conversion factor for thoron decay products of 40 nSv (Bq h m(-3))(-1). UNSCEAR Annex E suggests there is an emerging problem, namely, that the contribution of (220)Rn (thoron) gas to the (222)Rn (radon) gas measurement signal is not well known. Until recently, this has largely been ignored. This is an important consideration as measurements at work and homes are the basis for investigating lung cancer exposure-response relationships. Based on UNSCEAR Annex E, this paper provides an overview of the sources and levels of thoron and its associated decay products at home and work. In addition, this paper provides an overview of the thoron dosimetry considered by UNSCEAR Annex E and some recent results.

Commentary to the paper Assessment of annual effective dose from natural radioactivity intake through wheat grain produced in Faisalabad, Pakistan

Tufail et al. [1] studied and reported the concentrations of naturally occurring radionuclides (K, Ra and Th) in wheat grains. The method that was used was gamma-ray spectroscopy. Determining the activity concentration of Th by gamma-ray spectroscopy is, however, not possible. The two gammas from Th (63.8 and 141 keV) exhibit very low intensities (0.26 and 0.02%, respectively) and cannot hence be separated from the background using the set-up described in the paper. It is, hence, probable that the authors used the gammas from thorium series radionuclides of Ac, Pb or Tl. The activity of Ac follows that of Ra whereas the activity the latter two that of Th (and/or Ra). In short, they did not measure Th. The authors listed the activity concentrations of Th in wheat reported by e.g. Scheibel et al. [2] and PieterzakFlies et al. [3] and found that ‘‘activity values for K and Th in Indian wheat grain samples are quite comparable to that of studied samples’’. This is true with respect to Scheibel et al. [2], who employed the same erroneous method in analyzing Th as the authors did. The survey carried out by Pieterzak-Flies et al. [3] is, however, rigorous and the analyzing methods used are correct. The authors failed to recognize the activity concentration reported by Pieterzak-Flies et al. [3] was expressed as mBq kg, not as Bq kg. Market basket study of K, U and Th in foods sold in Pakistan has been carried out previously by Akhter et al. [4]. The ICP-MS method used for determining Th in this study was correct and the reported values were in-line with e.g. values compiled in UNSCEAR 2000. The effective dose to Pakistani adult population from Th from all food was 0.8 lSv a which is in gross contrast to the value reported by Tufail et al. [1] which was 43.1 lSv a from wheat consumption only. I would like to point out that this commentary also applies to several other papers on this topic (that I find fruitless to list here). Regrettably, it is a common mistake to assume full equilibrium of natural decays series’ radionuclides in biological samples, such as food. Radium uptake by vegetation is much more efficient than that of actinoids. This applies also to intake by livestock. Caution must therefore be exercised when calculating results of the natural decay series.

EVALUATION OF TOTAL EFFECTIVE DOSE DUE TO CERTAIN ENVIRONMENTALLY PLACED NATURALLY OCCURRING RADIOACTIVE MATERIALS USING A PROCEDURAL ADAPTATION OF RESRAD CODE

Due to a recent upward trend in the price of uranium and subsequent increased interest in uranium mining, accurate modeling of baseline dose from environmental sources of radioactivity is of increasing interest. Residual radioactivity model and code (RESRAD) is a program used to model environmental movement and calculate the dose due to the inhalation, ingestion, and exposure to radioactive materials following a placement. This paper presents a novel use of RESRAD for the calculation of dose from non-enhanced, or ancient, naturally occurring radioactive material (NORM). In order to use RESRAD to calculate the total effective dose (TED) due to ancient NORM, a procedural adaptation was developed to negate the effects of time progressive distribution of radioactive materials. A dose due to United States' average concentrations of uranium, actinium, and thorium series radionuclides was then calculated. For adults exposed in a residential setting and assumed to eat significant amounts of food grown in NORM concentrated areas, the annual dose due to national average NORM concentrations was 0.935 mSv y(-1). A set of environmental dose factors were calculated for simple estimation of dose from uranium, thorium, and actinium series radionuclides for various age groups and exposure scenarios as a function of elemental uranium and thorium activity concentrations in groundwater and soil. The values of these factors for uranium were lowest for an adult exposed in an industrial setting: 0.00476 microSv kg Bq(-1) y(-1) for soil and 0.00596 microSv m(3) Bq(-1) y(-1) for water (assuming a 1:1 234U:238U activity ratio in water). The uranium factors were highest for infants exposed in a residential setting and assumed to ingest food grown onsite: 34.8 microSv kg Bq(-1) y(-1) in soil and 13.0 microSv m(3) Bq(-1) y(-1) in water.

Thorium series radionuclides in the environment: Measurement, dose assessment and regulation

Environmental radioactivity research is more advanced for the 238U series than for the 232Th series, for a number of reasons. One reason is that some radionuclides of the 232Th series are more difficult to measure than the corresponding isotopes in the 238U series, and measurement techniques are less widely available. The 232Th series population doses, however, are sometimes significant. This paper analyses some main radionuclides in the 232Th series in comparison with corresponding nuclides in the 238U series, with regard to measurement techniques, dose coefficients and regulation needs.

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, Dão, 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 Urgeiriça confirmed by the enhanced values of 238U/ 232Th 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.

Naturally Occurring Radionuclides of Uranium and Thorium Series in Nonnuclear Industrial Processes

Distribution of naturally occurring radionuclides of the Th and U series in nonnuclear industrial processes is discussed. Some parallelism is found between the migration of naturally occurring radionuclides in the geological environment and their fate in industrial processes. In both cases, the behavior is governed by well-known laws for phase distribution of microcomponents. Differences in the behavior of particular members of the radioactive series in processing of natural raw materials are caused by specific chemical properties of parent and daughter nuclides. It was demonstrated with a number of examples that, in non-nuclear industrial processes, radionuclides can concentrate to a level requiring special protection measures.

Thoron in the living environments of Japan

High thoron concentrations have been investigated in various living environments with radon–thoron discriminative measurements; however, behavior of the thoron and its decay products and their effects on human health have not been clearly elucidated yet. In Japan, some kinds of building materials rich in natural radionuclides of thorium series, such as clay and soil plaster, are commonly used for construction and/or surface finishing of wall in traditional Japanese style houses. Measurements with different types of monitor for thoron and its decay products were carried out to investigate general characteristics of thoron in Japanese living environments. From the result of the measurements, thoron concentrations ranged from almost 0 to more than thousands Bq m −3. Extremely high concentrations can be found in the places near wall surface, and it decreases drastically as distance from the surface of the wall increases. Thoron concentration was found to be changed drastically with time. The equilibrium equivalent thoron concentrations (EETC) ranged from nearly 0 to about 6 Bq m −3. Correlation between the thoron concentration and EETC was not good. This report summarized the results of an investigation of thoron in living environments of Japan.

The annual effective dose from natural sources of ionising radiation in Canada

A review and analysis of published information combined with the results of recent gamma ray surveys were used to determine the annual effective dose to Canadians from natural sources of radiation. The dose due to external radiation was determined from ground gamma ray surveys carried out in the cities of Toronto, Ottawa, Montreal and Winnipeg and was calculated to be 219 microSv. A compilation of airborne gamma ray data from Canada and the United States shows that there are large variations in external radiation with the highest annual outdoor level of 1424 microSv being found in northern Canada. The annual effective inhalation dose of 926 microSv from 222Rn and 220Rn was calculated from approximately 14,000 measurements across Canada. This value includes a contribution of 128 microSv from 222Rn in the outdoor air together with 6 microSv from long-lived uranium and thorium series radionuclides in dust particles. Based on published information, the annual effective dose due to internal radioactivity is 306 microSv. A program developed by the Federal Aviation Administration was used to calculate a population-weighted annual effective dose from cosmic radiation of 318 microSv. The total population-weighted average annual effective dose to Canadians from all sources of natural background radiation was calculated to be 1769 microSv but varies significantly from city to city, largely due to differences in the inhalation dose from 222Rn.

Uranium and thorium series radionuclides in drinking water from drilled bedrock wells: correlation to geology and bedrock radioactivity and dose estimation.

Natural radioactivity in drinking water from 328 drilled wells was studied in correlation to source parameters. Poor correlation to both aquifer geology and bedrock radioactivity was observed. Concentrations of 238U, 226Ra, 228Ra, 222Rn and 210Po in groundwater samples was in the ranges <0.027-5.3, <0.016-4.9, <0.014-1.24, 5-8105 and <0.05-0.947 Bq.l(-1) respectively. In about 80% of the sites the radon concentration exceeds the Nordic recommended exemption level for radon in drinking water and 15% of the sites exceed the action limit. The effective doses from ingestion were calculated and presented in association with geology. Doses due to ingestion ranged between 0.05 and 20.4 mSv.y(-1), where the average contribution from 222Rn amounted to 75%. In comparison, the effective doses from inhalation of indoor 222Rn ranged between 0.2 and 20 mSv.y(-1). The average contribution from inhalation of 222Rn in air to the total effective dose (ingestion+inhalation) was 58 +/- 22%, 73 +/- 18% and 77 +/- 16% (1 SD) for the age categories 1 y, 10 y and adults respectively.