Uranium Series Radionuclides Research Articles

Overall natural radioactivity of a phosphate fertilizer industry in Korea

The phosphogypsum is produced as a by-product of the manufacturing phosphoric acid or phosphate fertilizer from the phosphate rock on the wet process. In general, it contains relatively high concentrations of uranium series radionuclides such as 226 Ra. This study surveyed overall radioactivity of the naturally occurring radionuclides in a facility using phosphate rock and evaluated the impact on the vicinity environment by the phosphogypsum.

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.

Radiation Safety of Old Uranium Mining Waste Dumps in Portugal

The risks associated to uranium mining and milling wastes require the radiological surveillance of the areas with these residues and the assessment of the radiation risk to the populations living in the region. This radiological surveillance is based on an environmental monitoring programme implemented by ITN. Annually, soils, water, and plants including horticulture products from the uranium mine areas are sampled and analyzed for radioactivity. As part of this programme, analyses of soils, irrigation waters, agriculture products (lettuce), green pasture, and cheese were performed in samples collected in the area of the old Urgeiriça uranium mine and milling facilities near Viseu, Centre-North of Portugal, in order to assess the transfer of uranium series radionuclides to man. In the Urgeiriça area, some soils and vegetables display radionuclide concentrations higher than in reference areas 226Ra was the radionuclide more concentrated by vegetables. Through ingestion of these products 226Ra may be the main contributor to the increment of radiation dose received by local population. The solutions implemented for environmental remediation of tailings piles and mining waste dumps in Urgeiriça and in other old uranium mine sites, with time are expected to render safe these areas and to allow the release of old mining concession areas for other uses by the public without radiation risks.

Analyses of radionuclides in soil, water, and agriculture products near the Urgeiriça uranium mine in Portugal

Analyses of soils, irrigation waters, agriculture products (lettuce), green pasture, and cheese were performed in samples collected in the area of the old Urgeirica uranium mine and milling facilities, Centre-North of Portugal, in order to assess the transfer of uranium series radionuclides in the environment and to man. Soils close to milling tailings display an enhancement of radioactivity. In the drainage basin of the stream Ribeira da Pantanha, receiving drainage from the tailings piles and discharges from the acid mine water treatment plant, there was enhancement of uranium series radionuclide concentrations in water and suspended matter. Agriculture products from kitchen gardens irrigated with water from the Ribeira da Pantanha show an increase of radioactivity, mainly due to uranium isotopes. Agriculture products from other kitchen gardens in this area, irrigated with groundwater, as well pasture and cheese produced locally from sheep milk did not show enhanced radionuclide concentrations. In the Urgeirica area, some soils display radionuclide concentrations higher than soils in reference areas and, in agriculture products grown there, 226Ra was the radionuclide more concentrated by vegetables. Through ingestion of these products 226Ra may be the main contributor to the increment of radiation dose received by local population.

Extensive radioactive characterization of a phosphogypsum stack in SW Spain: 226Ra, 238U, 210Po concentrations and 222Rn exhalation rate

Phosphogypsum (PG) is a by-product of the phosphate fertilizer industries that contains relatively high concentrations of uranium series radionuclides. The US-EPA regulates the agriculture use of PG, attending to its 226Ra content and to the 222Rn exhalation rate from inactive stacks. Measurements of 222Rn exhalation rates in PG stacks typically show a large and still poorly understood spatial and temporal variability, and the published data are scarce. This work studies an inactive PG stack in SW Spain of about 0.5 km 2 from where PG can be extracted for agriculture uses, and an agriculture soil 75 km apart, being representative of the farms to be amended with PG. Activity concentrations of 226Ra, 238U and 210Po have been measured in 30 PG samples (0–90 cm horizon) allowing for the construction of maps with spatial distributions in the PG stack and for the characterization of the associated PG inputs to agriculture soils. Averaged 226Ra concentrations for the stack were 730 ± 60 Bq kg −1 (d.w.), over the US-EPA limit of 370 Bq kg −1. 222Rn exhalation rate has been measured by the charcoal canister method in 49 sampling points with 3 canisters per sampling point. Values in PG stack were under the US-EPA limit of 2600 Bq m −2 h −1, but they were one order of magnitude higher than those found in the agriculture soil. Variability in radon emissions has been studied at different spatial scales. Radon exhalation rates were correlated with 226Ra concentrations and daily potential evapotranspiration (ETo). They increased with ETo in agriculture soils, but showed an opposite behaviour in the PG stack.

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 222Rn activity concentrations ranged from 0.24 to 1168 Bq L −1. The statistical analysis showed a log-normal distribution with a mean of (111 ± 7) Bq L −1 and a median of (36 ± 3) Bq L −1. A hydrogeological study revealed correlations between the activity concentration and the aquifer material's characteristics. A map of 222Rn in groundwater was elaborated and compared with the natural gamma radiation map for this region. About 35% of the samples showed 222Rn activity concentrations above the Euratom recommended limit of 100 Bq L −1. Three uranium series radionuclides ( 238U, 234U, and 226Ra) were also assayed by alpha-particle spectrometry, estimating the annual effective dose due to the presence of these natural radionuclides in drinking water.

A 28‐ka history of sea surface temperature, primary productivity and planktonic community variability in the western Arabian Sea

Uranium series radionuclides and organic biomarkers, which represent major groups of planktonic organisms, were measured in western Arabian Sea sediments that span the past 28 ka. Variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity, sea surface temperature (SST), and planktonic community structure were investigated. The average alkenone‐derived SST for the last glacial period was ∼3°C lower than that measured for the Holocene. Prior to the deglacial, the lowest SSTs coincide with the highest measured fluxes of organic biomarkers, which represent primarily a planktonic suite of diatoms, coccolithophorids, dinoflagellates, and zooplankton. We propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing, cold SSTs and enhanced primary productivity. In contrast, postdeglacial (<17 ka) SSTs are warmer during times in which biomarker fluxes are high. Associated with this transition is a planktonic community structure change, in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and Holocene than the average ratio during the last glacial period. We suggest that this temporal transition represents a shift from a winter northeast monsoon‐dominated (pre‐17 ka) to a summer southwest monsoon‐dominated (post‐17 ka) wind system.

Alpha emitters from uranium mining in the environment

Uranium mining and milling activities usually generate an enhancement of radionuclide concentrations in the environment that may cause increased radiological exposure to mankind. For risk assessment and radiological protection of man and environment in these areas, usually, it is needed to implement radiological surveillance of water, soils, agricultural products, aerosols, and mining waste discharges as well. Radionuclides to be monitored in priority are alpha-emitting nuclides of the uranium natural series. Radioactivity analysis of materials from uranium mining areas of Portugal shows departure from secular radioactive equilibrium amongst uranium series radionuclides, thus rendering invalid the assumption of equilibrium and requiring the actual determination of each radionuclide. Radionuclide measurements performed with high resolution alphaspectrometry, as reported herein, produce accurate results on specific radionuclides that are essential in computing radiation doses to critical groups of the population.

Exhalation of 222Rn from phosphogypsum piles located at the Southwest of Spain

Phosphogypsum (PG) is a waste product of the phosphoric acid production process and contains, generally, high activity concentrations of uranium series radionuclides. It is stored in piles formed over the last 40 years close to the town of Huelva (Southwest of Spain). The very broad expanse of the PG piles (about 1200 ha) produces a local, but unambiguous, radioactive impact to their surroundings. In 1992, the regional government of Andalusia restored an area of 400 ha by covering it with a 25-cm thick layer of natural soil and, currently, there is an additional zone of 400 ha in course of restoration (unrestored) and the same area of active PG stacks. Due to the high activity concentration of 226Ra in active PG stacks (average 647 Bq kg −1), a significant exhalation of 222Rn could be produced from the surface of the piles. Measurements have been made of 222Rn exhalation from active PG stacks and from restored and unrestored zones. The 222Rn exhalation from unrestored zones is half of that of the active PG stacks. Following restoration, the 222Rn exhalation is approximately eight times lower than the active PG stacks. The activity concentrations of natural radionuclides ( 226Ra, 40K, 232Th) in the mentioned zones have been determined. This study was also conducted to determine the effect of 226Ra activity concentration on the 222Rn exhalation, and a good correlation was obtained between the 222Rn exhalation and 226Ra activity, porosity and density of soil.

Uranium-series radionuclides in native fruits and vegetables of northern Australia

Wild fruits and vegetables play an important part in a traditional Aboriginal diet in northern Australia. Radionuclide uptake by these foods is important for radiological impact assessment of uranium mining operations in the region, particularly after minesite rehabilitation. In this paper, data are presented for concentrations in several fruits and root vegetables, and associated soils. In terms of radiological dose, 210 Po, 226 Ra and, to a lesser extent, 210 Pb were found to be of greater importance than the uranium and thorium isotopes. Other important factors that have emerged include food preparation and consumption habits of Aboriginal people which could potentially affect radionuclide intake estimates.

Soil-to-plant transfers of uranium series radionuclides in natural and contaminated settings

Uranium and related decay-chain radionuclides remain important subjects of study for a number of reasons. Uranium has the potential to be chemically toxic near mining and processing facilities, and the decay-chain radionuclides can contribute substantially to radiation dose. Establishing an air quality standard for U in Canada has also been tentatively based on its accumulation and toxicity in soil. This paper summarizes two studies. The first investigated the mobility in soil, uptake by plants and ecotoxicity of U near a U refining facility. Because of the presence of co-contaminants, a large number of other elements were measured to fully characterize the samples. In general, the soil solid/liquid partition coefficients, Kd, for U were high enough that leaching is not a dominant process. Plant/soil concentration ratios (CRs) were not consistently different compared to background sites. The second study measured plant/soil CRs for 210 Pb, 210 Po, 226 Ra, 228 Ra, 228 Th, 230 Th, 232 Th and 238 U on a series of sites across Canada, with emphasis on background sites with possible human food-chain connections. Secular equilibrium was rarely observed, especially in plants.

Sequential extraction of 226Ra in sediments from an estuary affected historically by anthropogenic inputs of natural radionuclides

Riverbed sediments from an estuary historically affected by wastes discharged by several phosphate fertiliser plants and enriched in uranium-series radionuclides were operationally speciated using a Tessier-based method. In each selective fraction the 226Ra content was determined by alpha-particle spectrometry after radiochemical isolation and electrodeposition onto stainless steel planchets. These studies were performed in 226Ra-polluted estuarine sediments collected one year after anthropogenic discharges had ceased in order to obtain useful information about the operational forms in which this radionuclide remains associated with the sediments at this time. The results obtained revealed that one year after 226Ra inputs had stopped, the radionuclide was associated mostly with the more refractory forms. Consequently, it is possible to foresee little potential remobilisation of 226Ra contamination from sediments to the aqueous phase in the future under normal environmental conditions.

Validation of isotope signatures in sediments affected by anthropogenic inputs from uranium series radionuclides

This paper aims to show the usefulness of 226Ra/228Ra activity ratios and confirm the possibility of using 230Th/232Th activity ratios as chronological markers in sediment cores from an estuarine system strongly contaminated by discharges from non-nuclear industries (fertiliser plants). The validation was carried out using an independent, well-established dating technique based on the analysis of the 137Cs fallout profile, which comprises the same time interval as that covered by both isotope ratios. The advantage of using the 226Ra/228Ra activity ratio profile instead of the Th-isotope profile is that determination can be accomplished with a non-destructive, simpler and less time-consuming technique, because both Ra isotopes can be determined by gamma-ray spectrometry.

Distribution and mobilization of U, Th and 226Ra in the plant–soil compartments of a mineralized uranium area in south-west Spain

The activity concentrations of natural uranium isotopes ( 238U and 234U), thorium isotopes ( 232Th, 230Th and 228Th) and 226Ra were studied in soil and vegetation samples from a disused uranium mine located in the Extremadura region in the south-west of Spain. The results allowed us to characterize radiologically the area close to the installation and one affected zone was clearly manifest as being dependent on the direction of the surface water flow from the mine. The activity concentration mean values (Bq/kg) in this zone were: 10 924, 10 900, 10 075 and 5289 for 238U, 234U, 230Th and 226Ra, respectively, in soil samples and 1050, 1060, 768 and 1141 for the same radionuclides in plant samples. In an unaffected zone, the activity concentration mean values (Bq/kg) were: 184, 190, 234 and 7251 for 238U, 234U, 230Th and 226Ra, respectively, in soil samples and 28, 29, 31 and 80 in plant samples. The activity concentrations obtained for 232Th and 228Th showed that the influence of the mine was only important for the uranium series radionuclides. The relative radionuclide mobilities were determined from the activity ratios. Correlations between radionuclide activity concentrations and stable element concentrations in the soil samples helped to understand the possible distribution paths for the natural radionuclides.

浅地中環境下におけるウラン系列核種の分配係数測定(Ⅰ)

浅地中環境下におけるウラン系列核種の分配係数測定(Ⅰ)

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.

Radionuclides in the terrestrial ecosystem near a Canadian uranium mill--Part III: Atmospheric deposition rates (pilot test).

Atmospheric deposition rates of uranium series radionuclides were directly measured at three sites near the operating Key Lake uranium mill in northern Saskatchewan. Sites impacted by windblown tailings and mill dusts had elevated rates of uranium deposition near the mill and elevated 226Ra deposition near the tailings compared to a control site. Rainwater collectors, dust jars, and passive vinyl collectors previously used at the Ranger Mine in Australia were pilot-tested. Adhesive vinyl surfaces (1 m2) were oriented horizontally, vertically, and facing the ground as a means of measuring gravitational settling, wind impaction, and soil resuspension, respectively. Although the adhesive glue on the vinyls proved difficult to digest, relative differences in deposition mode were found among radionuclides and among sites. Dry deposition was a more important transport mechanism for uranium, 226Ra, and 210Pb than rainfall, while more 210Po was deposited with rainfall.

Radionuclides in the terrestrial ecosystem near a Canadian uranium mill--Part I: Distribution and doses.

Soils, vegetation, small mammals, and birds were measured for uranium series radionuclides at three sites near the operating Key Lake uranium mill in northern Saskatchewan. Sites, impacted by windblown tailings and mill dust, had significantly higher concentrations of uranium, 226Ra, 210Pb, and 210Po in soils, litter, vegetation, tree needles and twigs, small mammals, and birds, compared to a control site. Samples were collected from both upland jackpine and black spruce bog habitats in triplicate at each site. Both habitats were similar in radionuclide accumulation. Absorbed doses averaged 0.92, 8.4, and 4.9 mGy y(-1) to small mammals and 2.0, 5.8, and 2.8 mGy y(-1) to Lincoln's sparrows at the control, tailings, and mill sites, respectively. These doses do not include doses from short-lived radon progeny. The majority of the dose increment at the tailings and mill sites was due to 226Ra, whereas it was 210Po at the control site. Thus, use of a radiation weighting factor of 20 for alpha radiation raised equivalent doses (in mSv y(-1)) by nearly a factor of 20.

Distributions of Uranium-Series Radionuclides in Rock and Migration Rate of Uranium at the Koongarra Uranium Deposit, Australia

Article Distributions of Uranium-Series Radionuclides in Rock and Migration Rate of Uranium at the Koongarra Uranium Deposit, Australia was published on December 1, 1998 in the journal Radiochimica Acta (volume 82, issue s1).

Overview of Radiation Safety in the Tin By-Product (Amang) Industry of South East Asia

Processing of by-product heavy minerals (amang) from tin mining involves potential exposure to external and internal sources of radioactivity. The radioactivity arises through the presence of thorium and uranium series radionuclides in the various minerals. Monazite is the most radioactive mineral, containing 3% to 7% thorium by weight, while ilmenite is generally the least radioactive mineral containing typically less than 0.05% thorium. External exposure occurs when workers are in close proximity to accumulations or stockpiles of the radioactive minerals, whereas internal exposure occurs when workers are involved in dusty processes. This paper summarizes the nature of the amang industry in South East Asia and presents the results of preliminary measurements of external radiation and airborne radioactivity in twelve Malaysian and Thai plants. Although constrained by a paucity of exposure data, it is concluded that radiation doses to some amang plant workers may approach or exceed international standards and that appropriate control measures are required as a matter of priority, Radiation doses may approach or exceed 100 mSv in situations where workers are exposed to excessive levels of ambient dust and no protective measures are used. Observations and recommendations are made relating to monitoring and surveillance, instruction and training, and engineering and administrative protection measures.