Frontiers of environmental radioactivity

Some frontiers of environmental radioactivity are outlined where radioecologists and chemists are required to solve environmental problems. The first theme is the need for research on biogeochemical cycling of both stable and radioactive nuclides. The second theme discusses measurement challenges in radioecology. The third theme is related to predictive abilities where much of the present radioecology work is aimed at estimates of impacts in the future. These three themes are linked because our predictive abilities of radionuclide transport require a better knowledge of nuclide cycling, and nuclide cycling can only be studied with the availability of good measurement techniques.     

Environmental radioactivity in the Eastern States of Nigeria

A survey of the environmental radioactivity in the Eastern States of Nigeria, consisting of Akwa Ibom and Corss River States has been done and that of Uyo (5°N, 7°50E), Nigeria, has been updated for the period of 1981 to 1991. An overall average of 329.7±13.3 mBq is the environmental radioactivity for the surrounding air in Akwa Ibom State, while 348.5±13.7 mBq is the activity for the air in Cross River State. There has been a marked increase of average environmental radioactivity in Uyo from 293.0±12.6 mBq to 373.7±14.8 mBq in recent years with a yearly mean of 324.1±13.7 mBq.     

A comparison of determination methods for uranium radioactivity in environmental soil samples using a gamma spectrometer

Journal of Radioanalytical and Nuclear Chemistry - Comparisons of statistical analysis results between five methods using gamma spectrometry and a control group for measuring the radioactivity of...     

Assessment of natural radioactivity in soil samples and comparison of direct and indirect measurement of environmental air kerma rate

This study presents the high purity germanium (HPGe) gamma spectrometric measurement of natural radioactivity mainly due to ²²⁶Ra, ²³²Th and ⁴⁰K in soil samples collected in Ferozepur and Faridkot district of Punjab, India. ²²⁶Ra activity varied from 28.6 to 51.1 Bq kg⁻¹ with the mean of 39.7 Bq kg⁻¹. The range and mean activity of ²³²Th were 42.9–73.2 and 58.2 Bq kg⁻¹, respectively. ⁴⁰K activity was in the range of 470.9–754.9 Bq kg⁻¹ with the mean of 595.2 Bq kg⁻¹. The air kerma rate (AKR) at 1 m height from the ground was also measured using gamma survey meter in all the sampling locations, which was ranging from 92.1 to 122.8 nGy h⁻¹ with the mean of 110.6 nGy h⁻¹. The radiological parameters such as Ra_eq and activity index of the soil samples were also evaluated, which are the tools to assess the external radiation hazard due to building materials. The mean and range of the Ra_eq values were 168.7 and 132.9–210.4 Bq kg⁻¹, respectively, whereas the activity index varied from 0.5 to 0.8 with the mean value of 0.62. These indices show that the indoor external dose due to natural radioactivity in the soil used for the construction will not exceed the dose criteria. The AKR was also evaluated from soil activity concentration and altitude correction of cosmic radiation contribution. The statistical tests such as Pearson correlation, spearman rank correlation, box and whisker plot, the Wilcoxon/Mann–Whitney test and chi-square test, were used to compare the measured AKR with evaluated AKR, which indicates good correlation.     

Geochemical studies on the Chernobyl radioactivity in environmental samples

Artificial radionuclides in deposition and airborne dust samples in 1986 were measured at Tsukuba and 11 stations in Japan. In May 1986, the Chernobyl radioactivity was observed in rain and air samples in Japan. The Chernobyl-derived Pu isotopes, which are characterized by higher²³⁸Pu/^239,240Pu (85) and²⁴¹Pu/²³⁸Pu (0.5) activity ratios than those of the nuclear test-derived Pu and⁹⁰Sr, were detected in deposition and airborne dust samples in Japan, as well as volatile radionuclides such as¹³¹I and¹³⁷Cs. However, the activities of Pu isotopes and⁹⁰Sr observed in Japan were about two and three orders of magnitude lower than those expected from the activity ratios in the total release at Chernobyl, which means that the residence time of Pu in the air was shorter than that of¹³⁷Cs. In order to understand the fractionation between the Chernobyl radionuclides we studied about individual wet and dry deposition. The results suggest that this cause is due to the difference of the particle size of radionuclide-bearing particles, which may be related to the release process of Chernobyl radionuclides.     

Simple determination of 90Sr in water in environmental radioactivity survey

Derivatives of dodecahydro-closo-dodecaborate(2-) anion were proposed as boron-rich compounds for boron-neutron capture therapy (BNCT) of malignant tumours. Labeling of such tumour-targeting compounds with radioisotopes would facilitate the investigation of their pharmacokinetics and help to optimize patient treatment protocols. Earlier, we reported the feasibility of labeling of closo-dodecaborate(2-) by isotopic exchange in molten acetamide. In this study, the feasibility of low-temperature isotopic exchange in the system [¹²⁵I]iodide - bis(triethylammonium) undecahydro-12-iodo-closo-dodecaborate was investigated. Our attempts to perform the exchange in solvents such as methylene chloride, acetone and acetonitrile in the presence of phase-transfer catalysts were unsuccessful. However, copper mediated exchange in aqueous media was possible. Isotopic exchange of triethylammonium undecahydro-12-iodo-closo-dodecaborate provided a 90-95% labeling yield after heating for three and half hours at 100 °C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of the uncertainty of environmental measurements of radioactivity

Results obtained by measurement of radioactivity have traditionally been associated with an expression of their uncertainty, based on the so-called counting statistics. This is calculated together with the actual result on the assumption that the number of counts observed has a Poisson distribution with equal mean and variance. Most of the nuclear scientific community has, therefore, assumed that it already complied with the latest ISO 17025 requirements. Counting statistics, however, express only the variability observed among repeated measurements of the same sample under the same counting conditions, which is equivalent to the term repeatability used in quantitative analysis. Many other sources of uncertainty need to be taken into account before a statement of the uncertainty of the actual result can be made. As the first link in the traceability chain calibration is always an important uncertainty component in any kind of measurement. For radioactivity measurements in particular we find that counting geometry assumes the greatest importance, because it is often not possible to measure a standard and a control sample under exactly the same conditions. In the case of large samples we have additional uncertainty components associated with sample heterogeneity and its influence on self-absorption and counting efficiency. In this paper we prepared an uncertainty budget for existing data for ¹³⁷Cs in Danish soil, which is shown to account adequately for all sources of uncertainty. This revised version was published online in July 2006 with corrections to the Cover Date.     

Natural radioactivity in building materials utilized in the State of Kuwait

A simple radiochemical procedure is described for the determination of⁹⁰Sr in brines, which are very highly concentrated in sodium, calcium, potassium, magnesium, chloride and sulfate ions. The method is based on the different solubility of yttrium as compared to that of strontium, calcium and magnesium in ammonium chloride solutions, and utilizes Eichroms resin TRU·Spec for the purification of the yttrium fraction. The overall time required for the⁹⁰Sr analysis (excluding the counting time) is less than one day. Because the procedure involves only rather simple steps, it is well suited for routine analyses of large sample numbers.     

Natural radioactivity in cultivated land in the vicinity of a phosphate fertilizer plant in Nigeria

Natural radioactivity in soil and vegetable samples in cultivated land in the vicinity of an active phosphate fertilizer plant in Kaduna, Nigeria was carried out to assess the potential radiological impact of the plant on its immediate environment. The activity counting was carried out using sodium iodide gamma spectrometry. The annual committed effective dose for two vegetables in the farmlands due to uranium (²³⁸U) and thorium (²³²Th) was assessed. The mean activity concentration of radionuclides in the soil samples ranges from 20.5±7.3 to 31.6±4.1 Bq kg^?1 for ²²⁶Ra, 19.6±1.6 to 53.2±3.7 Bq kg^?1 for ²³²Th and 203.9±6.3 to 253.6±9.5 Bq kg^?1 for ⁴⁰K. The annual intake of ²³⁸U and ²³²Th from consumption of okra were 1.9 Bq kg^?1 and 5.22 Bq kg^?1 and for tomatoes 2.66 Bq kg^?1 and 5.1 Bq kg^?1 respectively. The committed effective doses from consumption of okra and tomatoes were 0.1 μSv y^?1 and 0.12 μSv y^?1 respectively.     

Natural radioactivity in soil samples of Kocaeli basin, Turkey

The city of Kocaeli is in the western part of Anatolia in Turkey and has a population of approximately 1.000.000. There is no information about radioactivity in the Kocaeli soils samples so far. For this reason, the concentrations of the natural radionuclides in soil samples from 27 different sampling stations in Kocaeli Basin and its surroundings have been determined. The results have been compared with other radioactivity measurements in different country"s soils. The typical concentrations of ¹³⁷Cs, ²³⁸U, ⁴⁰K, ²²⁶Ra, ²³²Th found in surface soil samples ranged from 2±0.6 to 25±6 Bq/kg, from 11±4 to 49±10 Bq/kg, from 161±30 to 964±127 Bq/kg, from 10±4 to 58±11 Bq/kg, and from 11±3 to 65±13 Bq/kg, respectively.     

Determination of technetium-99 from the aspect of environmental radioactivity

A radioanalytical procedure has been developed for the determination of⁹⁹Tc in environmental samples. The procedure consists of precipitation, solvent extraction, ion exchange, electrodeposition and radiation measurement. Rhenium was used as a non-isotopic carrier of⁹⁹Tc. On the basis of 3σ counting error, the detection limits were 4.9·10^?5 Bq/l, 7.4·10^?3 Bq/kg wet and 7.4·10^?2 Bq/kg dry for water, biota and soil samples, respectively. Sea water, seaweeds (brown algae) and soils were collected to evaluate the present levels of⁹⁹Tc in Japan. The level of⁹⁹Tc in sea water was ca. 1·10^?4 Bq/l around Japan. Among the seaweeds (brown algae), Ishige okamurai showed the highest concentration of 5.8·10^?2 Bq/kg wet tissue and the highest concentration factor of 583. The level of⁹⁹Tc in the organic rich surface soil was ca. 1 Bq/kg dry soil in Fukuoka.     

Application of a low-level anti-coincidence gamma-spectrometer for environmental radioactivity measurement

Sensitive environmental radioactivity measurement using direct γ-spectroscopy needs to be carried out under particular low-level conditions as the quantity to be determined generally is very close to the natural background. Passive shielding of the detectors in addition to electronic suppression of Compton background resulting from scattering of high energy γ-rays in the gemanium detector seems to be the most promising approach to obtain statistically well defined peaks within reasonable measurement time. Results obtained with a heavily shielded anti-coincidence spectrometer installed at the Research Center Jülich, ideally suited for the measurement of low-level environmental radioactivity in various materials are described.     

Gamma spectrometric monitoring of environmental radioactivity using a mobile equipment

Using gamma-spectrometry systems on mobile units with accurate position information is a convenient means for surveying large areas for radioactive fallout or finding hot spots due to misplaced sources or releases from nuclear installations. Traditionally, large (tens of litres) high efficiency NaI(T1) detectors have been used for the purpose. HPGe detectors, however, offer certain advantages which can often compensate for their lower efficiency. This kind of remote sensing, regardless of detector type, requires specialized software. In order to provide accurate position information, the integration times must be kept as short as possible. This is especially true for fast air-borne measurements where counting periods below one second are desirable. We have constructed a special version of SAMPO software which controls data acquisition and runs real-time gamma-spectrum analysis including peak determination, nuclide identification, activity calculations, and reporting. The measurement/analysis cycle can be reduced down to 0.5 seconds on a standard Pentium-based PC. The analysis results are combined with accurate co-ordinates from a differential GPS system on a color coded map. The system is also able to give alarms based on different criteria. We have already measured and analyzed more than 500 000 spectra in field applications using jets, helicopters, cars, and also on-foot.     

Assessment of natural and fallout radioactivity in soil samples of Visakhapatnam

Environmental gamma radiation levels around the new Bhabha Atomic Research Centre site at Visakhapatnam have been assessed. Natural and anthropogenic radionuclide activity concentrations in soil samples collected were determined using high-resolution gamma spectroscopy. Average activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K were found to be 38, 38, 230 and 520 Bq kg^?1, respectively. No anthropogenic radionuclide except fallout ¹³⁷Cs having mean concentration range ≤ 0.2–2.2 Bq kg^?1 was detected in the soil samples. The observed values are compared with the values reported for different areas in India and other parts of the world. The annual total external gamma radiation dose to the members of public estimated using the above observations ranged from 0.13 to 0.38 mSv y^?1 with an average of 0.25 mSv y^?1.     

Measurement of natural radioactivity in soil from Peshawar basin of Pakistan

Natural radioactivity in the environment may change with time due to human activities, chemical and biological changes. From the view of radiation risk to population, the knowledge of natural radioactivity levels and the measurement of collective radiation dose received by the population is very vital. Radiological constraints on soil of thickly populated Peshawar basin in northern Pakistan were assessed through radiometric assay. Soil samples collected from different locations of four districts of this basin were analysed using an HPGe gamma spectrometer. Activity concentrations of ⁴⁰K, ²²⁶Ra and ²³²Th in these samples was 648 ± 121 (421–996), 45 ± 7 (32–60) and 59 ± 7 (46–72) Bq kg^?1, respectively that followed lognormal distribution. The average concentrations of primordial radionuclides were found to be higher than that reported for the worldwide soil. Radium equivalent activity and gamma index derived from these activity concentrations were lesser than their respective limits. The average absorbed dose rate and the annual effective dose for both indoor and outdoor cases were found to be higher than the values given in the UNSCEAR 2000 report. The results of the present study were compared with those for other locations of Pakistan along with that for the world. The radiological impact of the measured data was evaluated using hazard assessment models. A thoughtful discussion of the above mentioned evaluation is also given.     

Natural radioactivity studies of Bidar soil samples using gamma spectrometry

The activity of the terrestrial primordial radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K are measured for Bidar soil samples. The collected soil samples are analyzed using HPGe detector based on high resolution gamma spectrometric system. The activity of the three radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K were found to be in the range of BDL–47.68, 7.65–59.08 and BDL–260.65 Bq kg^?1 respectively. The mean gamma absorbed dose rate in air above 1 m from ground is estimated to be 34.47 nGy h^?1. Annual effective dose equivalent and the radium equivalent activity were within the limits in the present study and it is found that the activity of the radionuclides are comparable with the worldwide literature values. Also the external hazard indices for the soil samples of Bidar district were within the limit of unity.     

In-situ CeBr3 gamma-ray spectrometry for radioactivity analysis of soil

Journal of Radioanalytical and Nuclear Chemistry - A CeBr3 scintillation detector was applied for in situ gamma-ray spectrometry for radioactivity assessment of soil. The full energy peak...     

Influence of nuclear reactor accident at Chernobyl' on the environmental radioactivity in Toyama

The environmental radioactivity caused by the reactor accident at Chernobyl' was investigated from May 7 to May 31 of 1986 in Toyama. Measurement of radioactivities in airborne particles, rain water, drinking water, milk, and mugwort are carried out by gamma-ray spectrometry (pure Ge detector; ORTEC GMX-23195). Ten different nuclides (103Ru, 106Ru, 131I, 132Te-I, 134Cs, 136Cs, 137Cs, 140Ba-La) are identified from samples of airborne particles. In the air samples, a maximum radioactivity concentration of each nuclide is observed on 13th May 1986. The time of the reactor shut-down and the flux of thermal neutron at the reactor were calculated from 131I/132I and 137Cs/134Cs ratio. The exposure dose in Toyama by this accident is given as follows: internal exposure; [thyroid] adult-59 microSv, child-140 microSv, baby-130 microSv, [total body] adult-0.2 microSv, child, baby-0.4 microSv, external exposure; 7 microSv, effective dose equivalent; adult-9 microSv, child-12 Sv, baby-11 microSv.     

Effect of soil properties on radioactivity concentrations and dose assessment

This study evaluated the correlation between radioactivity concentrations and soil properties, and determined the total annual effective dose near an underground geologic repository for transuranic wastes. Soil samples were collected from two historical monitoring areas (Near Field and Cactus Flats). Alpha-particle spectrometry was used for the analysis of ²⁴¹Am, ^239+240Pu and ²³⁸U, while ¹³⁷Cs, ⁴⁰K, ²³²Th and ²²⁶Ra were detected by gamma ray spectrometry. Higher radioactivity concentrations and stronger positive correlations between radioactivity concentrations and soil properties were obtained in Cactus Flats compared to Near Field. The total annual effective dose was lower than the recommended limit of 1 mSv y^??1.

     

Iodine status and the effect of soil erosion on trace elements in Nanka and Oba towns of Anambra State, Nigeria

Iodine Deficiency Disorders (IDD) is common in all populations. Iodine and other trace elements naturally occur in the soil but erosion leaches off these elements from the soil. This results in a continued loss of trace elements from the soil. In the present study, the levels of iodine, selenium, zinc and lead in the environment (measured in soil, bitter leaves (Vernonia amygdalina), cassava roots (mannihot utilissima, staple food in Nigeria), and drinking water) and urinary iodine from school children (n=200), pregnant women (n=60) and women of child bearing age (n=60) were determined for Nanka prone to soil erosion and Oba all in Anambra State, Nigeria (used as control) to assess their risk to IDD. The levels of selenium, zinc and lead were analysed using Atomic Absorption Spectrophotometry while the levels of iodine in the environment and urinary iodine were estimated using the method of Dunn et al.,(1993). In this study there was a positive correlation between iodine and the metals. The results show that the mean concentrations of total soil zinc (0.69 +/- 0.16 ppm); lead (0.40 +/- 0.12 ppm) values in Oba were significantly (p < 0.05) higher than values from Nanka (Zn = 0.33 +/- 0.10 ppm; Pb = 0.21 +/- 0.09 ppm). However, total soil values for selenium and iodine in soil were not significantly different in the two communities. Mean concentration of total vegetable zinc (0.63 +/- 0.14 ppm) value in Oba is significantly (p < 0.05) higher than the value from Nanka (Zn = 0.31 +/- 0.07 ppm). However, total vegetable values for I, Se and Pb were not significantly different in the two communities. Also, mean concentration of total cassava zinc (0.65 = 0.15 ppm) in Oba was significantly (p < 0.05) higher than Zn (0.44 +/- 0.1l ppm) from Nanka. However, values for Se, Pb, and I were not significantly different in the two communities. Mean concentration of total water iodine (105.25 +/- 10.44 microg/L) in Oba was significantly (p < 0.05) higher than the value from Nanka (I = 89.8 +/- 6.42 microg/L). However, total water values for Se, Zn, and Pb were not significantly different in the two communities. The mean urinary iodine concentration of 170.65 +/- 27.17 microg/L in school children from Oba was significantly higher (p < 0.05) than the mean concentration of 156.12 +/- 16.48 microg/L found in school children from Nanka. However, the mean urinary iodine concentration of all the women (pregnant and non-pregnant) were not significantly different in the two communities but they are below the recommended daily intake. The results show that people living in Nanka and Oba, could be at risk of IDD.