Soil Activity Concentrations Research Articles

Annual effective dose values from 137Cs activity concentrations in soils of Manisa, Turkey

In this study, the activity concentrations of the fallout radionuclide 137Cs in 150 soil samples collected from 13 districts of Manisa Province were determined using a gamma ray spectrometer with a NaI(Tl) detector. The health risks to people resulting from external exposure were evaluated by estimating the outdoor absorbed gamma dose rate and annual effective dose rate (outdoor and indoor). The activity concentration of 137Cs varied from 3.6 ± 2.0 to 124.1 ± 11.0 Bq kg−1, with an average value of 43.3 Bq kg−1. The average values of the outdoor absorbed gamma dose rate and annual effective dose (outdoor plus indoor) were found to be 1.3 nGy h−1, and 8.0 µSv y−1, (6.38 + 1.59 µSv y−1), respectively. The results were compared with internationally recommended values.

Spatial datasets of radionuclide contamination in the Ukrainian Chernobyl Exclusion Zone

Abstract. The dataset “Spatial datasets of radionuclide contamination in the Ukrainian Chernobyl Exclusion Zone” was developed to enable data collected between May 1986 (immediately after Chernobyl) and 2014 by the Ukrainian Institute of Agricultural Radiology (UIAR) after the Chernobyl accident to be made publicly available. The dataset includes results from comprehensive soil sampling across the Chernobyl Exclusion Zone (CEZ). Analyses include radiocaesium (134Cs and 134Cs) 90Sr, 154Eu and soil property data; plutonium isotope activity concentrations in soil (including distribution in the soil profile); analyses of “hot” (or fuel) particles from the CEZ (data from Poland and across Europe are also included); and results of monitoring in the Ivankov district, a region adjacent to the exclusion zone. The purpose of this paper is to describe the available data and methodology used to obtain them. The data will be valuable to those conducting studies within the CEZ in a number of ways, for instance (i) for helping to perform robust exposure estimates to wildlife, (ii) for predicting comparative activity concentrations of different key radionuclides, (iii) for providing a baseline against which future surveys in the CEZ can be compared, (iv) as a source of information on the behaviour of fuel particles (FPs), (v) for performing retrospective dose assessments and (vi) for assessing natural background dose rates in the CEZ. The CEZ has been proposed as a “radioecological observatory” (i.e. a radioactively contaminated site that will provide a focus for long-term, radioecological collaborative international research). Key to the future success of this concept is open access to data for the CEZ. The data presented here are a first step in this process. The data and supporting documentation are freely available from the Environmental Information Data Centre (EIDC) under the terms and conditions of the Open Government Licence: https://doi.org/10.5285/782ec845-2135-4698-8881-b38823e533bf.

Effect of Bacillus subtilis and NTA-APG on pyrene dissipation in phytoremediation of nickel co-contaminated wetlands by Scirpus triqueter

A complex mix of organic pollutants and heavy metal made the remediation of contaminated wetlands more difficult. Few research focus on the remediation for pyrene enhanced by chemical reagents and pyrene degrading bacteria in the nickel co-contaminated soil. In this paper, the effect of chemical reagents (nitrilotriacetic acid and alkyl polyglucoside) and Bacillus subtilis on pyrene dissipation in phytoremediation of nickel co-contaminated soil by Scirpus triqueter was investigated. Similar seedlings of Scirpus triqueter were moved to uncontaminated soil and pyrene-nickel co-contaminated soil. The pots (14.8 cm diameter and 8.8 cm height) were set up in greenhouse and treated in different ways. After 60 days, plant biomass, radial oxygen loss (ROL), soil dehydrogenase activity (DHA) and pyrene concentration in soil were determined. Results showed that ROL rate and DHA in different groups was positively correlated with pyrene dissipation from soil. In the process of remediation, chemical reagents might have an indirect slight effect on pyrene dissipation (pyrene dissipation increased 21%) by affecting DHA firstly and redistributing pyrene fractions in the presence of pyrene degrading bacteria. Pyrene degrading bacteria were likely to affect pyrene dissipation by impacting ROL rate and DHA and played a more vital role in contributing to pyrene dissipation (pyrene dissipation increased 45%) from wetland. This study demonstrated that phytoremediation for pyrene in nickel co-contaminated soil by Scirpus triqueter can be enhanced by the application of NTA-APG and pyrene degrading bacteria and they could be reasonably restore the ecological environment of PAH-contaminated wetlands.

RADIOMETRIC IMPACT ASSESSMENT AROUND TWO QUARRY SITES, BENIN-OWO EXPRESS WAY, SOUTHWESTERN NIGERIA

Total reliance on quarry products as construction materials has prompted commercial quarry activities globally. However, potential risks introduced by radiation exposure to quarries in two different locations in Ondo State, Nigeria were assessed to evaluate the background radiation and distribution of naturally occurring radionuclides associated with these areas. A ground radiometric mapping of eleven traverses across the two quarry sites was carried out using Gamma ray spectrometer. Naturally occurring radionuclides 238 U, 232 Th and 40 K in natural quarried materials of coarse rock aggregates and soil samples collected at a maximum depth of 2 m and up to 500 m away from the quarry sites were measured using gamma spectrometry method. Spectrometric data were processed and presented in form of radiometric maps showing the distribution of radiation level in each location. Results show that activity concentrations varied from one location to another. The radiation level in the recently quarried coarse rock aggregates (QF1 and QF2) (372 cps and 382 cps) are higher than the previously quarried coarse rock aggregates (QP1 and QP2) (365 cps and 377 cps) of the quarry sites. Activity concentrations in soils are in the order 232 Th < 238 U < 40 K. The mean radioactivity concentration values of 232 Th, 238 U and 40 K are 0.0027±0.0003 Bq/kg, 0.028±0.0012 Bq/kg, 47.45±0.0313 Bq/kg and 0.0036±0.00036 Bq/kg, 0.026±0.0012 Bq/kg and 69.42±0.0313 Bq/kg respectively for soils within the quarries. At 500 m away from the quarry sites, mean values are 0.0008±0.75 Bq/kg, 0.020±0.0012 Bq/kg, 41.54±0.0313 Bq/kg and 0.0049±0.0004 Bq/kg, 0.052±0.0012 Bq/kg and 200.32±0.0313 Bq/kg respectively. The radiological hazard indices calculated were used to access the health implication of exposure to rock aggregates and soil of the study areas. The values obtained when compared with their corresponding world permissible values were found to be below the internationally recommended values. Therefore, the level of radiation and interaction with the rock aggregates and soils do not expose the workers and people within and around the quarries to health problem. Hence, the quarry products can be used as building material for housing and road constructions.

Air Absorbed Dose Rate Measurements and External Dose Assessment by Car-Borne Survey in the Gold Mining Areas of Betare-Oya, Eastern-Cameroon

In order to assess radiological exposure of the public due to natural occurring radioactive materials from gold mining areas of Betare-Oya and vicinity, Eastern Cameroon, a preliminary study was carried out in 2015 for laboratory measurements of activity concentrations of primordial radionuclides. In terms of annual effective dose, results revealed a mean value of 0.34 mSv y-1. However, it was necessary to make air absorbed dose rate contour map for a detailed evaluation of external dose. For this purpose, a car-borne survey using a 3-in × 3-in NaI(Tl) scintillation spectrometer was carried out in Betare-Oya and vicinity. Absorbed dose rates in air ranged from 23 to 80 nGy h-1 with a mean value of 44 ± 7 nGy h-1. The average values of activity concentrations in soil of 40K, 238U and 232Th were 197 ± 21 Bq kg-1, 37 ± 13 Bq kg-1 and 32 ± 7 Bq kg-1 respectively. 232Th was found to be the main contributor to the absorbed dose rate in air from outdoor terrestrial radiation in the study areas with a mean value of 43%. External annual effective dose ranged from 0.17 to 0.60 mSv y-1 with a mean value of 0.33 ± 0.05 mSv y-1, in agreement with the result (0.34 mSv y-1) of the previous study performed in the same areas using gamma spectrometry in laboratory for radioactivity measurements in soil samples. This survey first and widely revealed an aspect of natural radiation exposures in soil mining areas of Eastern Cameroon.

Radiological impact from natural radionuclide activity concentrations in soil and vegetables at former tin mining area and non-mining area in Peninsular Malaysia

The radionuclide concentrations of 226Ra, 232Th and 40K were measured in eleven different types of vegetables from nine sample locations in Peninsular Malaysia by using gamma spectrometry with high purity germanium detector. Radiological impact and cancer risk arising from the ingestion of vegetables was also determined in this study. The annual ingestion dose of vegetables from former tin mining area and non-mining area were found to be 0.64 and 0.61 µSv y−1. Corresponding cancer risk estimated for adults were 2.24 × 10−6 and 2.15 × 10−6 for former tin mining area and non-mining area, respectively. Both of them were lower than predicted value recommended at international level by ICRP, 3.5 × 10−3. The present study concludes that vegetables planted at both areas would not pose any significant radiological impact to the population, despite the higher concentration of radionuclide in soil. External hazard indices from soil in this study are less than one. Thus, the soils are suitable for use in agriculture.

Relationship among Phosphorus Circulation Activity, Bacterial Biomass, pH, and Mineral Concentration in Agricultural Soil.

Improvement of phosphorus circulation in the soil is necessary to enhance phosphorus availability to plants. Phosphorus circulation activity is an index of soil’s ability to supply soluble phosphorus from organic phosphorus in the soil solution. To understand the relationship among phosphorus circulation activity; bacterial biomass; pH; and Fe, Al, and Ca concentrations (described as mineral concentration in this paper) in agricultural soil, 232 soil samples from various agricultural fields were collected and analyzed. A weak relationship between phosphorus circulation activity and bacterial biomass was observed in all soil samples (R2 = 0.25), and this relationship became significantly stronger at near-neutral pH (6.0–7.3; R2 = 0.67). No relationship between phosphorus circulation activity and bacterial biomass was observed at acidic (pH < 6.0) or alkaline (pH > 7.3) pH. A negative correlation between Fe and Al concentrations and phosphorus circulation activity was observed at acidic pH (R2 = 0.72 and 0.73, respectively), as well as for Ca at alkaline pH (R2 = 0.64). Therefore, bacterial biomass, pH, and mineral concentration should be considered together for activation of phosphorus circulation activity in the soil. A relationship model was proposed based on the effects of bacterial biomass and mineral concentration on phosphorus circulation activity. The suitable conditions of bacterial biomass, pH, and mineral concentration for phosphorus circulation activity could be estimated from the relationship model.

Diagnostics techniques and dosimetric evaluations for environmental radioactivity investigations

A comprehensive study was conducted about the investigation of the natural/anthropo-genic radioactivity of various environmental matrices. Different diagnostics techniques were employed: high resolution HpGe gamma spectrometry, to quantify the activity concentration of radionuclides that emit gamma photons; alpha spectrometry, for the determination of the specific activity of α -emitters radioisotopes; liquid scintillation, to measure the activity concentration of tritium, radon and total alpha/beta in liquid samples; alpha spectrometry through the Rad7 setup, to estimate the gas radon activity concentration in air, water and soil; total alpha/beta counter, for the activity concentration quantification of radionuclides, in solid samples, emitting alpha/beta particles. From the dosimetric point of view, knowledge of the radioactivity level in the environmental matrices allows to evaluate any possible radiological hazard for the population, through the calculation of the appropriate parameters of radioprotection and their comparison with the safety limits reported by the literature.

Radiological health assessment due to gamma radiation levels of natural radioactivity of soil in vicinity of Nichahoma lignite belt, Kashmir Valley

Abstract The measurements of activity concentrations in soil of the lignite belt and soil of the villages surrounding the lignite belt have been carried out in order to present the radiological health hazards due to gamma radiation levels of the soil to general public. A low- background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector was employed for the measurements. The activity concentration of radionuclides have been determined and compared with the international and national recommended values. A correlation analysis was also performed in order to predict the contribution of the respective nuclides towards the measured dose rate and to the find the existence of these radioactive nuclides together in the study area.

137Cs distributions in soil and trees in forest ecosystems after the radioactive fallout – Comparison study between southern Finland and Fukushima, Japan

The nuclear accidents at Chernobyl and Fukushima released large amounts of 137Cs radionuclides into the atmosphere which spread over large forest areas. We compared the 137Cs concentration distribution in different parts of two coniferous forest ecosystems (needle litter, stems and at different depths in the soil) over short and long term periods in Finland and Japan. We also estimated the change in 137Cs activity concentrations in needle and soil between 1995 and 2013 in Southern Finland based on the back-calculated 137Cs activity concentrations. We hypothesized that if the 137Cs activity concentrations measured in 1995 and 2013 showed a similar decline in concentration, the 137Cs activity concentration in the ecosystem was already stable in 1995. But if not, the 137Cs activity concentrations were still changing in 2013. Our results showed that the vertical distribution of the 137Cs fallout in the soil was similar in Hyytiälä and Fukushima. The highest 137Cs concentrations were observed in the uppermost surface layers of the soil, and they decreased exponentially deeper in the soil. We also observed that 137Cs activity concentrations estimated from the samples in 1995 and 2013 in Finland showed different behavior in the surface soil layers compared to the deep soil layer. These results suggested that the 137Cs nuclei were still mobile in the surface soil layers 27 years after the accident. Our results further indicated that, in the aboveground parts of the trees, the 137Cs concentrations were much closer to steady-state when compared to those of the surface soil layers based on the estimated declining rates of 137Cs concentration activity in needles which were similar in 1995 and 2013. Despite its mobility and active role in the metabolism of trees, the 137Cs remains in the structure of the trees for decades, and there is not much exchange of 137Cs between the heartwood and surface layers of the stem.

Long-term behavior of 90Sr and 137Cs in the environment: Case studies in Switzerland

We present long-term records of the 137Cs and 90Sr activity concentrations in soil, grass and milk from two lowland and two alpine pastures of Switzerland. The data is used for better understanding the long-term behavior of these radionuclides in the environment. Transfer factors between compartments are used as qualitative indicators of the magnitude of transfer and as a way to compare different elements (e.g. Cs and Sr) in similar conditions. The long-term behavior was quantified by means of the effective half-life which integrates all processes that cause a decrease of activity in a given medium such as leaching, fixation, erosion and radioactive decay. Our study shows that 90Sr is more likely transferred from alpine soil to grass than 137Cs. This is explained by a stronger fixation of Cs in the soils. We observed higher transfers of 90Sr to grass in soils with lower Ca concentrations, and vice versa. In contrast, the transfer of 137Cs to grass was not affected by the variations of the K content in the soil. We provide evidence that shows that 137Cs, after intake by dairy cattle, is more likely transferred to milk than 90Sr. However, as the 90Sr and Ca transfers to milk are influenced by parameters/processes that were not taken into account in our study, our result cannot be entirely validated. The effective half-lives of 137Cs and 90Sr in soil, grass and milk corresponded with previous estimates in alpine soils. We have found that processes other than radioactive decay are responsible for a major decrease of the 90Sr activity in soil. For 137Cs, on the other hand, radioactive decay is among the most relevant process. Our data shows to be of interest in studying the trends of behavior of radionuclides in alpine regions.

Evaluation of radionuclides transfer from soil-to-edible flora and estimation of radiological dose to the Malaysian populace

Malaysia, a rapidly growing industrial country, is susceptible to pollution via large-scale industrial engagements and associated human activities. One particular concern is the potential impact upon the quality of locally resourced vegetables, foodstuffs that contain important nutrients necessary for good health, forming an essential part of the Malaysian diet. As a part of this, it is of importance for there to be accurate knowledge of radioactive material uptake in these vegetables, not least in respect of any public health detriment. Herein, using HPGe γ-ray spectrometry, quantification has been performed of naturally occurring radionuclides in common edible vegetables and their associated soils. From samples analyses, the soil activity concentration ranges (in units of Bq/kg) for 226Ra, 232Th and 40K were respectively 1.33–30.90, 0.48–26.80, 7.99–136.5 while in vegetable samples the ranges were 0.64–3.80, 0.21–6.91, 85.53–463.8. Using the corresponding activities, the transfer factors (TFs) from soil-to-vegetables were estimated, the transfers being greatest for 40K, an expected outcome given the essentiality of this element in support of vigorous growth. The TFs of 226Ra and 232Th were found to be in accord with available literature data, the values indicating the mobility of these radionuclides to be low in the studied soils. Committed effective dose and the associated life-time cancer risk was estimated, being found to be below the permissible limit proposed by UNSCEAR. Results for the studied media show that the prevalent activities and mobilities pose no significant threat to human health, the edible vegetables being safe for consumption.

Soil radioactivity levels, radiological maps and risk assessment for the state of Kuwait

An evaluation of the radioactivity levels associated with naturally occurring radioactive materials has been undertaken as part of a systematic study to provide a surface radiological map of the State of Kuwait. Soil samples from across Kuwait were collected, measured and analysed in the current work. These evaluations provided soil activity concentration levels for primordial radionuclides, specifically members of the 238U and 232Th decay chains and 40K which. The 238U and 232Th chain radionuclides and 40K activity concentration values ranged between 5.9 ↔ 32.3, 3.5 ↔ 27.3, and 74 ↔ 698 Bq/kg respectively. The evaluated average specific activity concentrations of 238U, 232Th and 40K across all of the soil samples have mean values of 18, 15 and 385 Bq/kg respectively, all falling below the worldwide mean values of 35, 40 and 400 Bq/kg respectively. The radiological risk factors are associated with a mean of 33.16 ± 2.46 nG/h and 68.5 ± 5.09 Bq/kg for the external dose rate and Radium equivalent respectively. The measured annual dose rates for all samples gives rise to a mean value of 40.8 ± 3.0 μSv/y while the internal and internal hazard indices have been found to be 0.23 ± 0.02 and 0.19 ± 0.01 respectively.

Cs-137 in milk, vegetation, soil, and water near the former Soviet Union's Semipalatinsk Nuclear Test Site.

The present study was carried out to evaluate Cs-137 activity concentration in soil, water, vegetation, and cow's milk at 10 locations within three regions (Abai, Ayaguz, and Urdzhar) to the southeast of the Semipalatinsk Nuclear Test Site (SNTS) in Kazakhstan. Cs-137 activity concentrations, determined using a pure Ge gamma-ray spectrometer, showed that, all samples collected did not exceed the National maximum allowable limits of 10,000 Bq/kg for soil, 100 Bq/kg for cow's milk, 74 Bq/kg for vegetation, and 11 Bq/kg for water. Cs-137 is, therefore, not considered a health hazard in these regions. The highest levels of contamination were found in the Abai region, where the highest activity concentration of Cs-137 was 18.0 ± 1.0 Bq/kg in soil, 7.60 ± 0.31 Bq/kg in cow's milk, 4.00 ± 0.14 Bq/kg in the vegetation, and 3.00 ± 0.24 Bq/kg in water. The lowest levels were measured within the Urdzhar region, where 4.00 ± 0.14 Bq/kg was found in the soil, 0.30 ± 0.02 Bq/kg in the cow's milk, 1.00 ± 0.03 Bq/kg in the vegetation, and 0.20 ± 0.02 Bq/kg in the water.

Lifetime Effective Dose Assessment Based on Background Outdoor Gamma Exposure in Chihuahua City, Mexico.

Determining ionizing radiation in a geographic area serves to assess its effects on a population’s health. The aim of this study was to evaluate the spatial distribution of the background environmental outdoor gamma dose rates in Chihuahua City. This study also estimated the annual effective dose and the lifetime cancer risks of the population of this city. To determine the outdoor gamma dose rate in air, the annual effective dose and the lifetime cancer risk, 48 sampling points were randomly selected in Chihuahua City. Outdoor gamma dose rate measurements were carried out by using a Geiger-Müller counter. Outdoor gamma dose rates ranged from 113 to 310 nGy·h−1. At the same sites, 48 soil samples were taken to obtain the activity concentrations of 226Ra, 232Th and 40K and to calculate their terrestrial gamma dose rates. Radioisotope activity concentrations were determined by gamma spectrometry. Calculated gamma dose rates ranged from 56 to 193 nGy·h−1. Results indicated that the lifetime effective dose of the inhabitants of Chihuahua City is on average 19.8 mSv, resulting in a lifetime cancer risk of 0.001. In addition, the mean of the activity concentrations in soil were 52, 73 and 1097 Bq·kg−1, for 226Ra, 232Th and 40K, respectively. From the analysis, the spatial distribution of 232Th, 226Ra and 40K is to the north, to the north-center and to the south of city, respectively. In conclusion, the natural background gamma dose received by the inhabitants of Chihuahua City is high and mainly due to the geological characteristics of the zone. From the radiological point of view, this kind of study allows us to identify the importance of manmade environments, which are often highly variable and difficult to characterize.

Measurement of fallout radionuclides, 239,240Pu and 137Cs, in soil and creek sediment: Sydney Basin, Australia

Soil and sediment samples from the Sydney basin were measured to ascertain fallout radionuclide activity concentrations and atom ratios. Caesium-137 (137Cs) was measured using gamma spectroscopy, and plutonium isotopes (239Pu and 240Pu) were quantified using accelerator mass spectrometry (AMS).Fallout radionuclide activity concentrations were variable ranging from 0.6 to 26.1 Bq/kg for 137Cs and 0.02–0.52 Bq/kg for 239+240Pu. Radionuclides in creek sediment samples were an order of magnitude lower than in soils. 137Cs and 239+240Pu activity concentration in soils were well correlated (r2 = 0.80) although some deviation was observed in samples collected at higher elevations. Soil ratios of 137Cs/239+240Pu (decay corrected to 1/1/2014) ranged from 11.5 to 52.1 (average = 37.0 ± 12.4) and showed more variability than previous studies.240Pu/239Pu atom ratios ranged from 0.117 to 0.165 with an average of 0.146 (±0.013) and an error weighted mean of 0.138 (±0.001). These ratios are lower than a previously reported ratio for Sydney, and lower than the global average. However, these ratios are similar to those reported for other sites within Australia that are located away from former weapons testing sites and indicate that atom ratio measurements from other parts of the world are unlikely to be applicable to the Australian context.

Accumulation and translocation peculiarities of 137Cs and 40K in the soil – plant system

Long-term investigations (1996–2008) were conducted into the 137Cs and 40K in the soil of forests, swamps and meadows in different regions of Lithuania, as well as in the plants growing in these media. The 137Cs and 40K activity concentrations, the 137Cs/40K activity concentration ratio and accumulation, and translocation in the system, i.e. from the soil to plant roots to above-ground plant part of these radionuclides, were evaluated after gamma-spectrometric measurements using a high purity germanium (HPGe) detector.Based on the obtained data, it can be asserted that in the tested plant species, the 137Cs and 40K accumulation, the transfer from soil to roots and translocation within the plants depend on the plant species and environmental ecological conditions. The 137Cs/40K activity concentration ratios in the same plant species in different regions of Lithuania are different and this ratio depends on the biotope (forest, swamp or meadow) in which the plant grows and on the location of the growing region. Based on the determined trends of statistically reliable inverse dependence between the activity concentrations in both soil and plants, it can be stated that the exchange of 137Cs and 40K in plants and soil is different. Different accumulations and translocations of investigated radionuclides in the same plant species indicate diverse biological metabolism of 137Cs and its chemical analogue 40K in plants. A competitive relationship exists between 137Cs and 40K in plants as well as in the soil.

Natural radioactivity in virgin and agricultural soil and its environmental implications in Sungai Petani, Kedah, Malaysia

A study on natural radioactivity in virgin and agricultural soil samples collected from Sungai Petani was conducted using high-purity germanium. The mean activity concentrations of 226Ra, 232Th, and 40K in virgin soils were 51.06±5.83, 78.44±6.42, and 125.66±7.26 Bq kg−1, respectively, while those in agricultural soils were 80.63±5.78, 116.87±7.87, and 200.66±18.24 Bq kg−1, respectively. The corresponding activity concentrations in agricultural soils were higher than those in virgin soils and those reported for other countries of the world. The average values of radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), outdoor annual effective doses (Eout), and indoor annual effective doses (Ein) in agricultural soils were 258.38 Ba kg−1, 0.708, 0.925, 0.162 mSv y−1, and 0.669 mSv y−1, respectively. The average values of outdoor external dose (Dout) and indoor absorbed dose (Din) rate in agricultural soils were 116.04 and 218.46 nGy h−1, respectively, which were higher than the permissible limit. Soil with Hex and Hin less than unity are suitable for use as building materials and in agriculture.

Levels of tritium in soils and vegetation near Canadian nuclear facilities releasing tritium to the atmosphere: implications for environmental models

Concentrations of organically bound tritium (OBT) and tritiated water (HTO) were measured over two growing seasons in vegetation and soil samples obtained in the vicinity of four nuclear facilities and two background locations in Canada. At the background locations, with few exceptions, OBT concentrations were higher than HTO concentrations: OBT/HTO ratios in vegetation varied between 0.3 and 20 and values in soil varied between 2.7 and 15. In the vicinity of the four nuclear facilities OBT/HTO ratios in vegetation and soils deviated from the expected mean value of 0.7, which is used as a default value in environmental transfer models. Ratios of the OBT activity concentration in plants ([OBT]plant) to the OBT activity concentration in soils ([OBT]soil) appear to be a good indicator of the long-term behaviour of tritium in soil and vegetation. In general, OBT activity concentrations in soils were nearly equal to OBT activity concentrations in plants in the vicinity of the two nuclear power plants. [OBT]plant/[OBT]soil ratios considerably below unity observed at one nuclear processing facility represents historically higher levels of tritium in the environment. The results of our study reflect the dynamic nature of HTO retention and OBT formation in vegetation and soil during the growing season. Our data support the mounting evidence suggesting that some parameters used in environmental transfer models approved for regulatory assessments should be revisited to better account for the behavior of HTO and OBT in the environment and to ensure that modelled estimates (e.g., plant OBT) are appropriately conservative.

Determination of 238U, 232Th and 40K activity concentrations in riverbank soil along the Chao Phraya river basin in Thailand

The activity concentrations of 238U, 232Th and 40K in riverbank soil along the Chao Phraya river basin was determined through gamma-ray spectrometry measurements made using a hyper-pure germanium detector in a low background configuration. The ranges of activity concentrations of 238U, 232Th and 40K were found to be 13.9 ↔ 76.8, 12.9 ↔ 142.9 and 178.4 ↔ 810.7 Bq kg−1, respectively. The anthropogenic radionuclide, 137Cs, was not observed in statistically significant amounts above the background level in the current study. The absorbed gamma dose rate in air at 1 m above the ground surface, the outdoor annual effective dose equivalent, the values of the radium equivalent activity and the external hazard index associated with all the soil samples in the present work were evaluated. The results indicate that the radiation hazard from primordial radionuclides in all soil samples from the area studied in this current work is not significant.