Estimation of annual effective dose due to ingestion of natural radionuclides in foodstuffs and water at a proposed uranium mining site in India

Abstract

Purpose: To study the distribution of ²¹⁰Po, ²²⁶Ra, ²³⁰Th and U(nat) (naturally occurring radioisotopes of uranium [²³⁴U, ²³⁵U and ²³⁸U]) in food and water around the Bagjata uranium mining area in India.

Materials and methods: Radionuclides were analyzed in food samples of plant and animal origin after acid digestion. Intake and ingestion dose of the radionuclides were estimated.

Results: ²¹⁰Po, ²²⁶Ra, ²³⁰Th and U(nat) in all the dietary components ranged widely from < 0.2–36, < 0.02–1.58, < 0.01–2.8 and < 0.017–0.39 Bqkg^-1, respectively. The range of ²²⁶Ra and U(nat) in water was < 3.5–206 and < 12.6–693 mBql^?1, respectively. The intake of radionuclides considering food and water was calculated to be 760 BqY^?1 while the ingestion dose was 601 μSvY^?1. The estimated doses reflect the natural background dose via route of ingestion, which is below the 1 mSvY^?1 limit set by the International Commission on Radiological Protection (ICRP). However, the doses are more than the dose constraint of 300 μSvY^?1 as suggested by the ICRP for members of the public for planned disposal of long-lived radioactive waste.

Conclusion: The study confirms that current levels of radionuclides do not pose significant radiological risk to the local inhabitants, but they need close investigation in the near future.     

Dose estimates for the local inhabitants from 210Po ingestion via dietary sources at a proposed uranium mining site in India

Abstract

Purpose: To study the distribution of ²¹⁰Po activity in food in Bagjata in East Singhbhum, India.

Materials and methods: ²¹⁰Po were analyzed in the food samples of plant origin such as cereals, pulses, fruits, vegetables and food of animal origin such fish, chicken, egg, etc., in and around Bagjata uranium mining area as a part of baseline study after acid digestion. The intake and ingestion dose of the radionuclide was estimated.

Results: The general range of ²¹⁰Po activity in all the dietary components ranged widely from <0.2–36 Bqkg^-1_fresh. In the food of plant origin, the minimum activity of ²¹⁰Po was estimated in vegetables while maximum in pulses. In food of animal origin, the observed minimum activity of ²¹⁰Po was in eggs and the maximum observed was in chicken samples. The intake of ²¹⁰Po considering all dietary components was found to be 464 Bq.Y^-1 while the ingestion dose was calculated to be 557 μSv.Y^-1, respectively. The estimated doses are reflecting the natural background dose via the route of ingestion, which is much below the 1 mSv limit set in the International Commission on Radiological Protection (ICRP) recommendations.

Conclusion: The study confirms that current levels of ²¹⁰Po do not pose a significant radiological risk to the local inhabitants.     

Aspects of the geographical variations of naturally occurring 210Pb/210Po in permanent teeth of juveniles in the UK

Purpose: To study geographical variations in the level of naturally occurring ²¹⁰Pb‐supported ²¹⁰Po in permanent teeth of juveniles in the UK.

Materials and methods: Permanent teeth extracted from 278 juveniles for orthodontic purposes were obtained from 48 counties in the UK. ²¹⁰Po activity concentration was measured on the outer enamel surface using TASTRAK α‐particle‐sensitive plastic track detectors.

Results: Geometric mean±SE activity concentrations in teeth from urban, suburban and rural areas, excluding the high radon area of Devon, were 8.41 +0.25/?0.24, 7.76 +0.37/?0.35 and 7.20 +0.49/?0.46?Bq?kg^?1, respectively. Overall, there was no significant association between α‐activity on the outer enamel surface of permanent teeth and proximity to the major UK motorways. However, when the data were considered with respect to the prevailing south‐westerly wind on the western side of the UK, a statistically significant association with respect to donors living downwind (on the easterly side) of the motorways was found. This effect was greater for sections of the M5 and M6 motorways that traverse urban areas. ²¹⁰Po levels in teeth were also associated with domestic radon concentration. This effect was comparable with that from traffic and urban pollution.

Conclusions: Higher levels of ²¹⁰Pb‐supported ²¹⁰Po are seen in permanent teeth of juveniles near sources of increased exposure in the UK. Inhalation uptake is an important pathway of exposure, especially with respect to domestic radon exposure. The results might be important in assessing integrated exposure to ²¹⁰Po in the skeleton and consequent high linear energy transfer dose to bone marrow.     

Enrichment and vertical profiles of 210Po and 210Pb in monazite areas of coastal Karnataka

A study on radiation level and radionuclide distribution in the environment of coastal Karnataka has revealed the presence of low-level monazite deposit in the Ullal beach area. The paper presents systematic studies on the distribution, enrichment and vertical profiles of ²¹⁰Po and ²¹⁰Pb, important daughter products of ²³⁸U, in Ombattu Kere, Summer Sand and the Bhagavathi Temple region of the Ullal beach area of coastal Karnataka. Sand samples collected at different depths from these locations were analyzed for ²¹⁰Po and ²¹⁰Pb activities to understand the distribution, enrichment and vertical profiles of these radionuclides in monazite area. The activity of ²¹⁰Po in the Ullal region is found to vary from 1.7 to 43.2 Bq kg^?1 with a mean value of 11.2 Bq kg^?1 and that of ²¹⁰Pb varies from 1.0 to 66.7 Bq kg^?1 with a mean value of 19.1 Bq kg^?1. The mean ²¹⁰Po/²¹⁰Pb ratio was observed to be 0.6. The absorbed gamma dose rate in the region varies in the range 39–460 nGy h^?1 with a mean value of 193 nGy h^?1.     

Radiological impact assessment to the environment due to waste from disposal of porcelain

The present study aimed to assess the radiological parameters from gamma rays due to the uncontrolled disposal of porcelain waste to the environment. Qualitative and quantitative identification of radionuclides in the investigated samples was carried out by means of a high-purity germanium (HPGe) detector. The average activity concentrations of the local porcelain samples were measured as 208.28?Bq/kg for ²²⁶Ra, 125.73?Bq/kg for ²³⁸U, 84.94?Bq/kg for ²³²Th and 1033.61?Bq/kg for ⁴⁰K, respectively. The imported samples had an average activity of 240.57?Bq/kg for ²²⁶Ra, 135.56?Bq/kg for ²³⁸U, 115.74?Bq/kg for ²³²Th and 1312.49?Bq/kg for ⁴⁰K, respectively. Radiological parameters and the radium equivalent Ra_eq for the investigated samples were calculated. The external and internal hazard indices, representative level index (I_γ), alpha index (I_α), and the exemption level (I_x), were estimated to be higher than the recommended value (unity), while the average activity concentrations for the studied samples were higher than recommended levels. In conclusion, we are concerned that disposal of porcelain in the environment might be a significant hazard.     

Preparedness to respond to possible acts of nuclear terrorism: Some strategies and recommendations

Purpose: To determine if pentoxifylline, interleukin 1α, selenium and misoprostol can minimize damage to physeal longitudinal growth during single radiation dose exposure in an animal model.

Materials and methods: Eighty‐seven weanling Sprague–Dawley rats were randomized into 15 drug/dose groups. All groups received a single 17.5‐Gy gamma‐irradiation exposure to the right knee, the left limb serving as an internal control. Pentoxifylline was injected 30?min before exposure, sodium selenite and interleukin 1α 24?h before exposure and misoprostol 2?h before exposure. Positive controls received 17.5?Gy. At 6 weeks, animals were sacrificed, the hind limb lengths were measured and detailed histomorphometric analysis was performed.

Results: Statistically significant reductions (p≤0.03) in mean limb length discrepancy compared with irradiation alone were seen following administration of pentoxifylline (50?mg?kg^?1), interleukin 1α (15?mcg?kg^?1), selenium (5?mg?kg^?1) and misoprostol (20?mg?kg^?1). Histomorphometric endpoints and growth rate remained altered at 6 weeks despite treatment, but length discrepancy reduction was highly correlated with the appearance of regenerative clones.

Conclusions: Each drug reduced the amount of anticipated growth arrest in the animal model and some compared favourably in magnitude with that previously demonstrated for the established radioprotectant drug amifostine. Restoration of growth appears related to appearance of regenerative clones.     

Dietary habits and energy balance in an under 21 male international soccer team

Soccer presents a metabolic challenge which is not necessarily matched by players’ habitual dietary intake. To examine the effects of a bespoke diet, 22 players completed the Ball Sport Endurance and Sprint Test (BEAST_90mod) protocol, followed by 4 days of regulated nutritional intake. The diet consisted of 10 g?kg^?1 body mass (BM) and 1.7 g?kg^?1 BM of carbohydrate and protein, respectively. On day 5, players followed a prematch nutritional strategy of 7 g?kg^?1 BM of carbohydrate and 1 g?kg^?1 BM of protein divided into three meals and then repeated the BEAST_90mod. The players’ pre-intervention intake consisted of 49 ± 7.1% or 3.5 g ± 1.0 g?kg^?1 BM for carbohydrate and 19 ± 3.8% of total daily energy intake or 1.3 g ± 0.5 g?kg^?1 BM for protein. Following the tailor-made dietary intervention, players ran an additional 887 ± 233 m (8.1%; d = 2.4). An acute dietary intervention provided a positive effect on a valid simulated soccer match play test.     

Spatial Distribution of Naturally Occurring 210Po and 226Ra in Children's Teeth

Deciduous and permanent teeth extracted from juveniles for orthodontic purposes have been analysed using α-sensitive plastic track detectors for the spatial distribution of total α-activity and naturally occurring ²¹⁰Pb-supported ²¹⁰Po and ²²⁶Ra. The distribution of these radionuclides is nonuniform, with ²¹⁰Po being primarily associated with outer enamel and ²²⁶Ra with the pulp. The observations suggest that ²¹⁰Pb/²¹⁰Po concentrates at the interface of enamel with saliva or blood, by means of unidirectional ionic exchange with calcium. In contrast, ²²⁶Ra concentrates in the predentine band at the interface with pulp and with systemic blood circulation, where its uptake is permitted by the incomplete calcification in this band. Activity concentration was measured in 900 teeth. Total concentration on the outer enamel surface of deciduous teeth, permanent teeth from children ?10 years and permanent teeth from children > 10 years give respective mean values of 8·63±0·26, 5·76±0.48 and 7·00±0·15 Bq kg^?1. ²²⁶Ra concentration on the corresponding longitudinal sections comprising pulp, dentine and annular enamel give respective mean values of 0·715±0·055, 0·418±0·083 and 0·514±0·029 Bq kg^?1. Mean activity concentration in 32 foetal teeth was 2·05±0·31 Bq kg^?1. The results form the basis of more detailed studies of (1) age-dependent uptake of α-radionuclides in teeth and their microdistribution, and (2) the geographical variation in activity concentration with respect to environmental factors such as domestic radon exposure.     

Changes in physical activity, maximal isometric strength and maximal oxygen uptake from late teenage to adulthood: an eight-year follow-up study of adolescents in Denmark

A randomly selected group of 88 men and 115 women, aged 23–27 years in 1991, were tested as teenagers in 1983, and then followed-up in 1991. A mean increase of 15% in maximal voluntary isometric strength was found in men, and no change was found in women over the 8 years. Body weight increased 14% in men and 6% in women. Strength in relation to body weight (N · kg^?1) did not change in men, but a small decrease of 3% was found in women. Strength in abdominal muscles decreased in blue-collar workers but increased in students. Maximal oxygen uptake (V?_o2max (ml · min^?1kg^?1) decreased 9% in men and 3% in women. The values in 1991 were 47.9 and 39.5 ml · min^?1kg^?1 for men and women, respectively. Participation in leisure sport activities decreased 1.7 h · week^?1 in men and 1.2 h · week^?1 in women. Seventy percent of the men and 74% of the women participated in regular leisure sport activity, which was a marked increase from 8 years before, when only 54% of the men and 57% of the women were similarly active. The overall decrease in V?_O2max in men was due primarily to a decrease among blue-collar workers and unemployed men: 19%vs 4% in other occupational groups. Only 20% of the blue-collar workers participated in sport activities for more than 4 h · week^?1, and 47% did not participate at all. In women, changes in strength and V?_O2max were related to motherhood. Abdominal muscle strength decreased, but arm flexor strength increased in women who had become mothers. V?_O2max decreased 14% in mothers vs 2% in other women. Changes over 8 years in V?_O2max and strength did not relate to changes in physical activity, but a significant relationship between decrease in physical activity and gain in body fat was found in men. Changes in body weight and body fat were the only variables that correlated with changes in strength. None of the observed changes related to changes in V?_O2max (ml · min^?1kg^?1). For the 23- to 27-year-olds, the level of physical activity assessed in h · week^?1 was almost as high in women as in men.     

226Ra 228Ra 210Pb和210Po在水生生物及食物链中转移规律的探讨

目的 为了解天然放射性核素²²⁶Ra、²²⁸Ra、²¹⁰Pb与²¹⁰Po在水生物及食物链中转移和蓄积情况。方法 定点采集养殖水产品及栖息环境中水与底质沉积物, 按不同的实验需要, 每个鲜样分别剥取肉, 骨(壳),鳞片和胃肠。烹饪样品, 洗净、称重、清炖, 熟后分离出骨(壳),余为食物。样品分别测定²²⁶Ra、²²⁸Ra、²¹⁰Pb和²¹⁰Po含量。数据按统计学要求处理, 配对数据, 作了配对显着性检验。结果 ²²⁶Ra、²²⁸Ra和²¹⁰Pb主要沉积于骨(壳)中, 浓集系数为10²～10³,肉中为10⁰～10².²¹⁰Po主要蓄积在水生物胃肠中, 浓集系数在10²～10⁴,鱼类胃肠与贝类肉中可达10⁴.水产食品烹饪加工过程²²⁶Ra、²²⁸Ra和²¹⁰Pb在食物链中转移不明显, 经配对显着性检验, 差异无显着性(P0.05);然而210Po在淡水鱼类和虾类中转移是明显的, 肉配对检验有非常显着性差别(P<0.01).结论水生物对²²⁶Ra、²²⁸Ra、²¹⁰Pb和²¹⁰Po有很强浓集能力。     

238U, 235U, 137Cs and 133Xe in soils from two campuses in University of Douala—Cameroon

An evaluation of ²³⁸U, ²³⁵U, ¹³⁷Cs and ¹³³Xe in soils from two campuses in University of Douala—Cameroon using gamma spectroscopy based Broad Energy Germanium Detector (BEGe6530) has been performed. The mean activities in soils from Campuse 1 were 40.16±8.98 Bq/kg for ²³⁸U, 3.39±0.33 Bq/kg for ²³⁵U, 0.46±0.33 Bq/kg for ¹³⁷Cs and 0.14±0.16 Bq/kg for ¹³³Xe. In Campus 2, the mean activities in soils were 31.45±12.24 Bq/kg, 3.02±1.00 Bq/kg, 0.30±0.26 Bq/kg and 0.35±0.24 Bq/kg for ²³⁸U, ²³⁵U, ¹³⁷Cs and ¹³³Xe, respectively. Using the in situ survey meter, the mean values of the absorbed dose rate measured was 71.43 nGy/h for Campus 1 and 62.72 nGy/h for Campus 2. The evaluated average outdoor effective dose for Campus 1 and 2 were 87.60 µSv/yr and 76.93 µSv/yr, respectively. The overall results obtained in this work were generally low compared to that of UNSCEAR.     

Analysis of low-level natural radioactivity in small mineral samples for use in thermoluminescence dating,using high-resolution gamma spectrometry

The use of high resolution γ-ray spectrometry in the detailed analysis of low level samples for the ²³⁸U and ²³²Th decay chains is discussed. A spectrometer is described, based on a “p” type intrinsic germanium well-detector contained in a cryostat manufactured from selected low background materials, and with a sample capacity of up to 10 g. Problems of sample self absorption are discussed and the calibration of the spectrometer detailed. Checks to confirm the calibration are described and illustrative analyses of samples of interest to thermoluminescence dating given. Typical overall uncertainties are between 1 and 5 Bq kg⁻¹, depending on the radionuclide concerned.     

Evaluation of Dosimetric Parameters for Various Ir Brachytherapy Sources Under Unbounded Phantom Geometry by Monte Carlo Simulation

As per TG-43 dose calculation formalism, it is essential to obtain various dosimetric parameters such as the air-kerma strength, dose rate constant, radial dose function, and anisotropy function, as they account for accurate determination of dose rate distribution around brachytherapy sources. Most of the available reported Monte Carlo simulations were performed in liquid water phantoms with a bounded region of 30-cm diameter. In this context, an attempt was made to report the dosimetric parameters for various commercially available pulsed-dose rate (PDR) and high-dose rate (HDR) sources under unbounded phantom conditions, as the data may be used as input to treatment planning systems (TPSs) for quality control assistance. The air-kerma strength per unit activity, S_k/A, was computed for various Iridium-192 (¹⁹²Ir) sources in dry air medium. The air-kerma strength and dose rate constant for old PDR is (9.77 ± 0.03) 10⁻⁸ U/Bq and 1.124 ± 0.001 cGyh⁻¹U⁻¹; for new PDR, the values are (9.96 ± 0.03) 10⁻⁸ U/Bq and 1.124 ± 0.001 cGyh⁻¹U⁻¹; for old MHDR, the values are (9.80 ± 0.01) 10⁻⁸ U/Bq and 1.115 ± 0.001 cGyh⁻¹U⁻¹; for new MHDR, (9.80 ± 0.01) 10⁻⁸ U/Bq and 1.112 ± 0.001cGyh⁻¹U⁻¹; for old VHDR, the values are (10.32 ± 0.01) 10⁻⁸ U/Bq and 1.035 ± 0.002 cGyh⁻¹U⁻¹; for new VHDR, the values are (10.34 ± 0.02) 10⁻⁸ U/Bq and 1.096 ± 0.001 cGyh⁻¹U⁻¹. The computed radial dose function values and anisotropy function values are also in good agreement with available data.     

Aerobic exercise capacity at sea level and at altitude in Kenyan boys, junior and senior runners compared with Scandinavian runners

The aim of this study was to characterize Kenyan runners in regard to their oxygen uptake and blood and ammonia responses when running. Untrained Kenyan boys (14.2±0.2 years) and Scandinavian runners were included for comparison. The studies were performed at altitude (～2.000 m.a.s.l.) and, for several Kenyan and Scandinavian runners, at sea level as well. At altitude sedentary adolescent Kenyan boys had a mean maximal oxygen uptake (Vo_2max) of 47 (44–51) ml · kg^?1· min^?1, whereas similarly aged boys regularly walking or running but not training for competition reached above 62 (58–71) ml · kg^?1· min^?1 in Vo^2max. Kenyan runners in active training had 68±1.4 ml · kg^?1· min^?1 at altitude and 79.9±1.4 ml · kg^?1· min^?1 at sea level, with individuals reaching 85 ml · kg^?1· min^?1. The best Scandinavian runners were not significantly different from the Kenyan runners in Vo_2max both at altitude and at sea level, but none of the Scandinavians reached as high individual values as observed for some Kenyan runners. The running efficiency, determined as the oxygen cost at a given running speed, was less in the Kenyan runners, and the difference became more pronounced when body weight was expressed in ml · kg^?0.75 min^?1. Blood lactate concentration was in general lower in the Kenyan than in the Scandinavian runners, and the Kenyans also had extremely low ammonia accumulation in the blood even at very high exercise intensities. It is concluded that it is the physical activity during childhood, combined with intense training as teenagers that brings about the high Vo_2max observed in some Kenyan runners. Their high aerobic capacity, as well as their good running economy, makes them such superior runners. In addition, their low blood lactate and ammonia accumulation in blood when running may also be contributing factors.     

Causation of Cancer. British Medical Bulletin,Vol. 14, No. 2

Summary

Peroxyl radicals of poly(U), poly(A), and single- and double-stranded DNA have been produced by photolysing H₂O₂ in oxygenated aqueous solution in presence of the substrates. The peroxyl radicals are formed by the reaction of OH radicals with the polynucleotides followed by addition of oxygen.

The lifetime of the peroxyl radicals and the rate constant of their reactions with the thiols cysteamine, gluthathione and dithiothreithol have been measured by time-resolved e.s.r. spectroscopy. The unusually long lifetimes range from 0·2 to 3·3 s. The activation energy for the decay for all four substrates is 10·3 ± 1 kcal/mol (43 kJ mol^?1). The reaction rate constants with the thiols range from k = 0·8 × 10⁴ to 1·3 × 10⁵ dm³ mol^?1 s^?1. The reactions of the thiols with the peroxyl radical of poly(U) are known to prevent strand break formation. This shows that the peroxyl radicals of poly(U) observed by e.s.r. are intermediates in the pathway leading to strand break formation.     

云南省部分地区大米和玉米放射性核素水平调查

目的 调查云南省部分地区大米和玉米放射性核素水平,充实云南地区食品放射性水平基线数据,评估其对居民产生的健康风险。方法 依据国家标准《生物样品中放射性核素的γ能谱分析方法》《高纯锗γ能谱分析通用方法》《食品中放射性物质检验总则》《土壤中放射性核素的γ能谱分析方法》,对云南省20个县（区）大米和玉米样品进行放射性核素检测,对检测结果进行处理与分析。结果 大米样品中²³⁸U、²³²Th、²²⁶Ra、⁴⁰K和¹³⁷Cs活度浓度均值分别为（0.416±0.403）、（0.045±0.034）、（0.030±0.013）、（28.4±18.8）和（0.014±0.019）Bq/kg,玉米样品中²³⁸U、²³²Th、²²⁶Ra、⁴⁰K活度浓度均值分别为（0.308±0.230）、（0.035±0.031）、（0.053±0.072）、（56.8±38.6）Bq/kg,¹³⁷Cs的活度浓度低于探测下限。结论 云南省20个县（区）大米和玉米中²³⁸U、²³²Th、²²⁶Ra、⁴⁰K和¹³⁷Cs的放射性水平均在国家标准正常范围内,食入后不会对居民的健康造成影响。     

Uptake of radioactivity by marine surface sediments collected in Ghazaouet, west coast of Algeria

Samples of surface marine sediments of different grain sizes collected in Ghazaouet, a small bay on the western coast of Algeria, have been examined to measure concentrations of natural and artificial gamma-emitting radionuclides. The aim of this study is to determine the level of radioactivity and its repartition in the sedimentary area. The samples analyzed by direct counting gamma spectrometry, showed relatively high activities for natural radioactivity and revealed measurable quantities of ¹³⁷Cs, ranging from 0.66–8.47 Bq kg⁻¹ dry weight. In addition, some of the samples of different nature were sieved in different grain-sizes, to study the uptake of radioactivity. It is found that the sediments of less than 100 μm grain-size have the highest level of uptake of radioactivity.     

Repeated exposure to low‐level extremely low frequency‐modulated microwaves affects baseline and scopolamine‐modified electroencephalograms in freely moving rats

Purpose: To compare in the electroencephalogram of rats the effects of scopolamine (an acetylcholine receptor antagonist) alone and after repeated exposure to low‐level microwaves modulated at extremely low frequency.

Materials and methods: Averaged frequency spectra (0.5–30?Hz) of the electroencephalogram were studied in freely moving rats with carbon electrodes implanted into the somatosensory cortex. The rats were repeatedly (3 days, 30?min?day^?1) exposed to low‐intensity (?0.3?mW?cm^?2) microwaves (915?MHz, 20‐ms pulse duration), amplitude modulated (square‐wave) at extremely low frequency (4?Hz).

Results: The exposure to extremely low frequency microwaves alone significantly enhanced the fast electroencephalographic rhythms (18–30?Hz). This effect was observed neither in subsequent sham‐exposure experiment nor in radiation‐naïve animals. In the microwave‐exposed rats, scopolamine (0.1?mg?kg^?1, subcutaneously) did not cause a slowing in the electroencephalogram that was shown in non‐exposed rats. A similarity between the scopolamine‐induced electroencephalogram effect in the microwave‐exposed rats and that of physostigmine (enhancing the acetylcholine level in the brain) in radiation‐naïve animals was noted. This paradoxical phenomenon stimulates new experimentation for understanding its mechanism(s).

Conclusions: The data obtained provide additional evidence that repeated low‐level exposure to extremely low frequency microwaves can modify an activity of cholinergic system in the brain.     

Chronic exposure by ingestion of environmentally relevant doses of 226Ra leads to transient growth perturbations in fathead minnow (Pimephales promelas,Rafinesque, 1820)

Abstract

Purpose: To assess the impact of environmentally relevant levels of ingested ²²⁶Ra on a common freshwater fish species.

Methods: Fathead minnow (Pimephales promelas, Rafinesque) were obtained at the first feeding stage and established on a commercial fish food diet containing ²²⁶Ra in the activity range 10 mBq/g^?1, –10,000 mBq/g^?1. They remained on this diet for 24 months and were sampled invasively at 1,6,18 and 24 months to assess growth, biochemical indices and accumulated dose and non-invasively also at 12 and 15 months to assess growth.

Results: Fish fed 10 and 100 mBq/g^?1 diet showed a small transitory deregulation of growth at 6 and 12 months. Fish fed higher activities showed less significant or insignificant effects. There was a trend at 18 months which was stronger at 24 months for the population distribution to change in all of the ²²⁶Ra fed groups so that smaller fish were smaller and bigger fish were bigger than the controls. There were also significant differences in the ratios of protein:DNA at 24 months which were seen as a trend but were not significant at earlier time points.

Conclusions: Fish fed a radium diet for 2 years show a small and transitory growth dysregulation at 6 and 12 months. The effects predominate at the lower activities suggesting hormetic or homeostatic adjustments. There was no effect on growth of exposure to the high activities ²²⁶Ra. This suggests that radium does not have a serious impact on the ecology of the system and the level of radium that would be transferred to humans is very low. The results may be important in the assessment of long-term environmental impacts of ²²⁶Ra exposure.     

Radioanalytical studies of fallout 63Ni

Fallout of Nickel-63 (T_1/2 = 100 a) produced in small amounts at nuclear weapon tests following the neutron activation of weapon construction material was investigated by studying carpets of lichen collected during 1961 to 1988 at the Lake Rogen district in central Sweden (62.3°N, 12.4°E). The maximal level of ⁶³Ni in the lichen carpet, which occurred in 1964, was about 0.6 Bq kg⁻¹, dry weight, and decreased to 0.1 Bq kg⁻¹ in 1988. The deposition pattern for ⁶³Ni was similar to other fallout radionuclides such as ¹³⁷Cs, ⁹⁰Sr and ^239+240Pu. The concentrations of stable Ni were relatively constant at 0.5 to 1.0 μg g⁻¹ throughout the years resulting in, for example, a specific activity (⁶³Ni/stable Ni) of 0.5 Bq mg⁻¹ in 1964 and 0.1 Bq mg⁻¹ in 1988. The total area content of ⁶³Ni was estimated to be 1.0 Bq m⁻² and the activity ratio ⁶³Ni/⁶⁰Co was estimated to be 0.03 in 1966. The Chernobyl accident in April 1986 did not significantly increase the levels of ⁶³Ni.For the measurement of these extremely low-levels of ⁶³Ni, 200 g of dry material (about 1 kg fresh) were ashed and leached with aqua regia after hydroxides had been precipitated with ammonia, leaving Ni in the aqueous phase. Nickel was extracted as a dimethylglyoxime complex by chloroform and back-extracted with HCl. Finally, Ni was electroplated onto copper discs from an ammonium sulfate medium at high pH. The radiochemical yield was determined by atomic absorbtion spectrometry of stable Ni before and after electrodeposition. Nickel-63 on the discs was measured by using a windowless anticoincidence-shielded Geiger-Müller gas-flow counter. Using a counting time of 3000 minutes the minimum-detection level was 1 mBq.