[Impact of Radioactive Elements on Microbial Complexes in Cryogenic Soils of Yakutia]

It has been found that microorganisms in cryogenic soils of Yakutia are resistant to the long-term impact of cesium and thorium. The number of microorganisms in the studied ecological-trophic groups does not depend on the concentrations of radioactive elements. Differences in the number of microorganisms are determined by the physicochemical conditions that are created in different horizons of the soils studied. The long-term impact of radiation (for 36 and 66 years) on microorganisms inhabiting the permafrost soils of Yakutia has developed their adaptive capacity to high concentrations of these radioactive elements.

Terrestrial gamma radiation dose rate in Ryukyu Islands, subtropical region of Japan

In order to explain the distribution of natural radiation level in the Asia, in situ measurements of dose rate in air due to terrestrial gamma radiation have been conducted in a total of 21 islands that belong to Ryukyu Islands (Ryukyu Archipelago), subtropical rejoin of southwest Japan. Car-borne surveys have also been carried out in Okinawa-jima, the biggest island of the archipelago. Based on the results for these measurements, arithmetic mean, the maximum and the minimum of the dose rates at 1 m in height from the unpaved soil ground in the archipelago were estimated to be 47, 165 and 8 nGy h(-1), respectively. A comparative study of car-borne data obtained prior to and subsequent to the 2011 Fukushima nuclear accident, as for Okinawa-jima, indicated that the nuclear accident has no impact on the environmental radiation at the present time.

Calculation of internal dose from ingested soil-derived uranium in humans: Application of a new method

The aim of the present study was to determine the internal dose in humans after the ingestion of soil highly contaminated with uranium. Therefore, an in vitro solubility assay was performed to estimate the bioaccessibility of uranium for two types of soil. Based on the results, the corresponding bioavailabilities were assessed by using a recently published method. Finally, these bioavailability data were used together with the biokinetic model of uranium to assess the internal doses for a hypothetical but realistic scenario characterized by a daily ingestion of 10 mg of soil over 1 year. The investigated soil samples were from two former uranium mining sites of Germany with (238)U concentrations of about 460 and 550 mg/kg. For these soils, the bioavailabilities of (238)U were quantified as 0.18 and 0.28 % (geometric mean) with 2.5th percentiles of 0.02 and 0.03 % and 97.5th percentiles of 1.48 and 2.34 %, respectively. The corresponding calculated annual committed effective doses for the assumed scenario were 0.4 and 0.6 µSv (GM) with 2.5th percentiles of 0.2 and 0.3 µSv and 97.5th percentiles of 1.6 and 3.0 µSv, respectively. These annual committed effective doses are similar to those from natural uranium intake by food and drinking water, which is estimated to be 0.5 µSv. Based on the present experimental data and the selected ingestion scenario, the investigated soils-although highly contaminated with uranium-are not expected to pose any major health risk to humans related to radiation.

[Natural radioactivity of potassium 40K in curative and natural mineral waters and dose estimation]

Natural mineral and curative waters often characterize elevated level of mineral components. If the mineralization grows, the concentration natural radionuclides, which are one population's exposure sources on ionizing radiation, also grows. The main purposes work were: (1) determine the concentration isotope potassium 40K in samples of water, (2) calculate effective doses caused by intake of water with potassium 40K, (3)- explore correlation between potassium 40K concentration and total dissolved solids (TDS). The concentration radioisotope 40K in analysed samples determined by means of gamma spectrometry. Received concentrations have values from the interval 0.65 to 28.42 Bq/dm3. Measured values compared to values calculated from physico-chemical analyses composition of water, which amounted from 0.07 to 22.87 Bq/dm3. The calculated effective dose resulting from intake water with potassium 40K, concentration 2.26 Bq/dm3 equaled 294 nSv by treatment and caused by inhalation water with concentration 40K 1.45 Bq/dm3 reached value 9 nSv by treatment.

Elemental transfer from Chinese soil via the diet to the whole human body

Based on results from recent studies of elemental dietary intake and organ or tissue content for adult Chinese men, quoted nationwide elemental concentrations in Chinese soil and newly published national average consumption of dietary foods, values of both transfer coefficients and discrimination factor (DF) for transfer from soil via the diet to both critical organs and the whole body have been calculated for important elements in radiation protection, including alkaline earths, alkali metals, rare earths and other related elements. These calculations have used both the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) model and the DF method. In the UNSCEAR model, the basic parameters used to describe the transport of radionuclides are the transfer coefficients P(ij), which describe the relationship of concentrations or other amounts between compartment i and the following compartment j, whereas the DF is the ratio between the transfer coefficients for one element and a chemically similar element. From a comparison of the transfer coefficients of different elements for a particular transport pathway, those for alkaline earths are generally speaking higher than those for halogen elements and alkali metals, whereas those for rare earth elements, U and Th are lower. Relative to Ca, the DFs of transfer from soil to diet and from diet to critical organs or the whole body for the other alkaline earth elements and Pb are all less than 1, the DFs for the other elements decrease with increasing or decreasing atomic number. For alkali metals, the DFs of transfer from diet to critical organs and the whole body seem to increase with increasing atomic number, but those from soil to diet decrease with increasing atomic number.

Effects of low chronic doses of ionizing radiation on antioxidant enzymes and G6PDH activities in Stipa capillata (Poaceae)

Stipa capillata (Poaceae) seeds were harvested from a control area (displaying a gamma dose rate of 0.23 micro Sv h(-1)) (C plants) and from two contaminated areas (5.4 and 25 micro Sv h(-1)) on the Semipalatinsk nuclear test site (SNTS) in Kazakhstan. The plants were grown for 124 d in a greenhouse under controlled conditions and exposed to three different treatments: (0) control; (E) external gamma irradiation delivered by a sealed 137Cs source with a dose rate of 66 micro Sv h(-1); (E+I) E treatment combined with internal beta irradiation due to contamination by 134Cs and 85Sr via root uptake from the soil. The root uptake led to a contamination of 100 Bq g(-1) for 85Sr and 5 Bq g(-1) for 134Cs (of plant dry weight) as measured at harvest. The activity of SOD, APX, GR, POD, CAT, G6PDH, and MDHAR enzymes was measured in leaves. Under (0) treatment, all enzymes showed similar activities, except POD, which had higher activity in plants originating from contaminated areas. Treatment (E) induced an enhancement of POD, CAT, GR, SOD, and G6PDH activities in plants originating from contaminated areas. Only control plants showed any stimulation of APX activity. Treatment (E+I) had no significant effect on APX, GR, CAT, and POD activities, but MDHAR activity was significantly reduced while SOD and G6PDH activities were significantly increased. The increase occurred in plants from all origins for SOD, with a greater magnitude as a function of their origin, and it occurred only in plants from the more contaminated populations for G6PDH. This suggests that exposure to a low dose rate of ionizing radiation for almost a half century in the original environment of Stipa has led to natural selection of the most adapted genotypes characterized by an efficient induction of anti-oxidant enzyme activities, especially SOD and G6PDH, involved in plant protection against reactive oxygen species.

Uptake of cesium-137 and strontium-90 from contaminated soil by three plant species; application to phytoremediation

A field test was conducted to determine the ability of three plant species to extract 137Cs and 90Sr from contaminated soil. Redroot pigweed (Amaranthus retroflexus L.), Indian mustard [Brassica juncea (L.) Czern.], and tepary bean (Phaseolus acutifolius A. Gray) were planted in a series of spatially randomized cells in soil that was contaminated in the 1950s and 1960s. We examined the potential for phytoextraction of 90Sr and 137Cs by these three species. Concentration ratios (CR) for 137Cs for redroot pigweed, Indian mustard, and tepary bean were 2.58, 0.46, and 0.17, respectively. For 90Sr they were substantially higher: 6.5, 8.2, and 15.2, respectively. The greatest accumulation of both radionuclides was obtained with redroot pigweed, even though its CR for 90Sr was the lowest, because of its relatively large biomass. There was a linear relationship between the 137Cs concentration in plants and its concentration in soil only for redroot pigweed. Uptake of 90Sr exhibits no relationship to 90Sr concentrations in the soil. Estimates of time required for removal of 50% of the two contaminants, assuming two crops of redroot pigweed per year, are 7 yr for 90Sr and 18 yr for 137Cs.

[Histomorphological study of mice inbred CBA liver under combined chronic influence of low dose gamma radiation and incorporated thorium nitrate]

We studied histomorphology of the CBA line mice liver after 30 and 90 days of the low dose gamma-radiation influence combined with incorporated Th(NO3)4 in doses 0.03; 0.1; 0.3 grams per kilogram of the living mouse weight. Morphophysiological and morphometric changes were shown. The liver mass and index were significant by increased after 30 days influence. The same changes after 90 days influence were not shown. The morphometric parameters (dynamics of double-nucleus and polyploid hepatocytes, nucleoluses numbers) gave evidence of the liver energy disbalance.

Radiostrontium transfer to sheep's milk as a result of soil ingestion

Soil ingestion as a source of radiostrontium contamination of ruminant milk products was studied by measuring the transfer coefficient to ovine milk. This is a follow-up report from a previous experiment (Assimakopoulos et al., 1993), which investigated radiocaesium transfer to sheep's milk as a result of soil ingestion. Milk samples from three lactating ewes, housed in individual metabolism cages, were used. Fifty grams per day of heavily contaminated sandy topsoil, collected in the Chernobyl area, were administered orally to the animals for a period of 1 week. The daily intake of 90Sr was 78 Bq day-1. During this contamination period, daily milk production and excreta output were measured. Excreta and milk was collected for an additional 7-day decontamination period, while they were fed on uncontaminated feed. The transfer coefficient was obtained through a best fit (minimum chi 2) of the data to predictions of a linear compartment model. The value obtained was fm = 0.041 +/- 0.016 d kg-1 for radiostrontium transport to milk. This result suggests that soil ingestion can be a major source of radiostrontium contamination in sheep and other free-grazing ruminants.

Ingested soil as a source of 137Cs to ruminants

Ingestion of soil has been identified as a potentially important source of radionuclides, particularly to grazing ruminants. Soil artificially contaminated with radiocaesium was administered orally each day for 33 days to Bergamasca sheep and the transfer to milk measured. Two soil types were used, with a clay content of 11% and 16%, respectively. Transfer coefficient (fm) values to sheep milk, calculated at the equilibrium (period from 7th to 21st day after soil administration), were 3.72 x 10(-4) days l-1 (S.D. = 7.2 x 10(-5) days l-1) and 6.11 x 10(-4) days l-1 (S.D. = 9.1 x 10(-5) days l-1), respectively for the two soils. These low values indicate that radiocaesium is not removed from the binding sites on the clay minerals in the gut of the sheep.

Radiocaesium transfer to sheep's milk as a result of soil ingestion

Soil ingestion as a source of radiocaesium contamination to ruminants was studied by measuring the transfer coefficient to sheep milk. Eight lactating ewes, housed in individual metabolism cages, were used. Fifty grams per day of heavily contaminated sandy topsoil, collected in 1990 from the Chernobyl area, were administered orally to the animals for a period of 1 week. The daily dose intake in 137Cs was 1835 Bq day-1. During this contamination period, daily milk production and excreta output were measured. The ewes were monitored for an additional 7 day decontamination period, while they fed on uncontaminated feed. Transfer coefficients were obtained through a best fit (minimum chi 2) of the data to predictions of a linear compartment model. The values obtained were fm = (2.6 +/- 0.7) x 10(-2) and f mu = (5 +/- 2) x 10(-2) days kg-1 for radiocaesium transport to milk and urine, respectively. These results suggest that soil ingestion can be a major source of radiocontamination for sheep and other free-grazing ruminants. Comparison of our results with soil-to-milk transfer coefficient values derived in two recent independent experiments suggests that there might be a strong dependence of radiocaesium availability on soil composition.

Measurements of the gastrointestinal absorption and tissue distribution of plutonium, americium and polonium in experimental animals

In order to set limits on environmental and occupational intakes of radionuclides, information is needed on their uptake and metabolism in man. Human data are very limited, particularly for long-lived alpha-emitting isotopes such as those of the actinides. Animal experiments are therefore an important source of data on the distribution of radionuclides in tissues, and the effects of factors such as subject age and the chemical form of elements on gastrointestinal absorption. The NRPB performs experimental programs using mainly rats and guinea pigs. In order to study the gastrointestinal absorption and tissue distribution of plutonium, americium and polonium, a variety of analytical techniques are employed. These include ion exchange and solvent extraction leading to alpha spectrometry and liquid scintillation counting. The investigation of low specific-activity environmental or industrial materials, and the very low bioavailability of elements such as the actinides, means that very low levels of activity have to be measured. Contamination at the dissection and tissue separation stage, as well as during the radiochemistry, has to be rigorously avoided. Where very detailed information is needed on the location of radionuclides within tissues, such as in the study of alpha-emitter distribution in the intestine, autoradiography is used. The application and relevance of different measurement techniques to animal studies will be discussed and examples of the results presented.