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.     

Studies of the vertical distribution of134Cs,137Cs,238Pu,239, 240Pu,241Pu,241Am and210Pb in ombrogenous mires at mid-latitudes

Six peat cores taken from three unmodified blanket and raised bogs in Ireland were sectioned and analyzed for a range of radionuclides including¹³⁴Cs,¹³⁷Cs,²³⁸Pu,²³⁹Pu,²⁴¹Am, and²¹⁰Pb.¹³⁴Cs and¹³⁷Cs were measured by high resolution gamma-spectrometry, while the transuranium nuclides were determined after chemical separation by alpha-spectrometry.²⁴¹Pu, present on the electroplated discs together with Pu(), was measured directly by low-level liquid scintillation counting. Core chronologies were established by measuring the unsupported²¹⁰Pb component using low energy photon spectrometry (LEPS). From the resulting profiles, relaxation depths and migration rates for the above mentioned radionuclides have been determined and differences in the values of these parameters interpreted.²³⁸Pu/^239,240Pu and²⁴¹Pu/^239,240Pu ratios have been examined carefully and are discussed in some detail. Finally, the contribution from Chernobyl to the total radiocaesium inventory in each core has been established using the¹³⁴Cs/¹³⁷Cs ratio observed in the initial fallout from Chernobyl.     

Determination of90Sr and137Cs in mushrooms following the Chernobyl fallout

After the Chernobyl accident high concentrations of radionuclides were found in Sweden in mushrooms and the contents of⁹⁰Sr and¹³⁷Cs were measured. The level of⁹⁰Sr was generally low and, in proportion to¹³⁷Cs, 2–3 orders of magnitude lower than in the fallut. The contents of¹³⁷Cs varied among species and extreme local variations occurred. The ratio¹³⁴Cs/¹³⁷Cs diverged from other biological samples leading to the conclusion that old fallout was involved in the uptake.     

Deposition of90Sr and plutonium isotopes derived from the Chernobyl accident in Japan

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (^239,240Pu,²³⁸Pu,²⁴¹Pu and⁹⁰Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of⁹⁰Sr differed from that of volatile radionuclides such as¹³¹I and¹³⁷Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of⁹⁰Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher²⁴¹Pu deposition in most of the stations, as well as high²³⁸Pu/^239,240Pu activity ratios were observed. The²⁴¹Pu/²³⁸Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than¹³⁷Cs.     

Separation of137Cs and90Sr from mineralizates of biological materials by dicarbolide of cobalt

The distribution of some radionuclides in the course of¹³⁷Cs and⁹⁰Sr extraction and scrubbing between organic and water phase was determined.¹³⁷Cs and⁹⁰Sr were isolated from the mixture of radionuclides in mineralized biological materials. Dicarbolide of cobalt i. e. 3,3′-commo-bis[undecahydro-1,2-dicarbo-3-closo-dodecaborate] was used as an extracting agent. Quantities of the extracted radionuclides were determined by gamma spectrometric technique. Single and repeated extraction of⁹⁰Sr with 0.01M resp. 0.1M dicarbolide of cobalt in nitrobenzene and scrubbing of coextracted radionuclides by 0.5M HNO₃ were studied. The extraction of⁹⁰Sr was investigated from solutions of a hydrofobizing agent in the same way. Finally, the quantitative extraction of¹³⁷Cs followed by the extraction of⁹⁰Sr from mixtures of radionuclides in a mineralized biological material was studied. Extraction yields from dry and wet mineralizates of biological tissues, from urine and milk were compared. Suitable working conditions for the separation procedures were selected.     

Modified and reverse radiometric flow injection analysis

Determination of¹³⁷Cs and⁶⁰Co by using modified and reverse radiometric flow injection analysis is described. Two component RFIA was also realized using⁶⁰Co and¹³⁷Cs radionuclides.     

Natural and artificial radionuclides in soils from Paraná State,Brazil

Soil samples from Paraná State, Brazil, were collected in 1991 and compared with others collected at the same location in March 1977 and at the end of 1983. Pedological analyses were practiced on these samples and¹³⁷Cs and²³²Th,²²⁶Ra and⁴⁰K activities were determined by gammaray spectrometry. A latitude dependence of¹³⁷Cs was found as well. It was impossible to determine the¹³⁷Cs contribution from Chernobyl nuclear accident because of low fallout and intense leaching, erosion and re-suspension in soils of regions with high annual precipitation. Natural radionuclides did not show such effects.     

Radionuclide concentrations in several seaweeds and their annual variations

To examine the radionuclide concentrations in the environment, seaweeds were collected once a year since 1976 at two different places. A marked change was observed in the number of radionuclides in seaweeds. The increase of radionuclides is attributed to contamination by radioactive fallout from Chinese nuclear explosion tests. The radionuclide concentrations were strongly dependent on the species of seaweeds. A gradual decrease of the¹³⁷Cs/⁴⁰K activity ratio was observed in spite of the input of additional¹³⁷Cs fallout from Chinese nuclear tests. This implies that the amounts of¹³⁷Cs introduced into seawater by these detonations were small in comparison with those already contained in seawater. The cesium content in seawater was estimated by using specific activities of¹³⁷Cs in seaweeds and¹³⁷Cs concentration in seawater. The results show good agreement with the reported values by direct analysis of seawater.     

Radioactivity of cattle fodder and milk after the Chernobyl accident

The radioactivities of⁹⁰Sr,¹³⁷Cs and¹³⁴Cs have been measured in soil, fodder and milk from the south-western region of Slovenia, Yugoslavia after the Chernobyl accident. Maximal concentrations of Sr-isotopes in samples and the rate of their decrease in a period up to two years after the accident are given. The transfer of radionuclides from soil to grass and from fodder to milk is discussed.     

Influence of plant roots upon the mobility of radionuclides in soil, with respect to location of contamination below the surface

The movement of⁸⁵Sr,¹³⁷Cs,⁵⁴Mn and⁶⁰Co in the 50 cm soil profile was studied with and without the presence of plant roots (triticum aestivum) in order to investigate the influence of roots and depth contamination upon the migration of radionuclides. The water table was maintained manually at 3 cm from the bottom. The physiochemical characteristics (E_h Fe^–2, NH ₄ ⁺ , pH and moisture content) as well as the total and extractable radioactivity were investigated. In the discrete contamination, where the location of contamination varied within the soil profile (0–5, 25–30 or 45–50 cm from the top), the influence of location upon the movement of these radionuclides was also studied. It was found that the changes in the soil physicochemical characteristics influenced the mobility of the four radionuclides. The extractability of⁵⁴Mn and⁶⁰Co was significantly increased in the reducing region of the soil, whereas that of⁸⁵Sr,¹³⁷Cs was not. Plant roots excerted significant effects upon the soil characteristics, via, reducing the E_h pH and moisture content of the soil; increasing the extractability of both⁵⁴Mn and⁶⁰Co from the depth of 35 cm downwards. Radionuclide migration occurred via physicochemical and biological transport. The biological transport via plant roots was of particular importance for¹³⁷Cs. Location of contamination had a significant influence upon the mobility of radionuclides. The migration of radionuclides was in the sequence of contamination in middle>bottom>top. The degree of the influence varied with radionuclides concemed. In the top layer contamination, the rank of the migration from the contamination layers, on the other hand⁵⁴Mn,⁶⁰Co and¹³⁷Cs were more mobile and the movement was:⁸⁵Sr⁵⁴Mn⁶⁰Co>¹³⁷Cs. In the middle and bottom contamination layers, on the other hand,⁵⁴Mn and⁶⁰Co and¹³⁷Cs were more mobile and the movement was⁸⁵Sr⁵⁴Mn⁶⁰Co>¹³⁷Cs. The results provide evidence conceming the soil-root interaction influencing the transfer efficiency of radionuclides from below the soil surface into the human food chain.     

239,240Pu,241Am and137Cs in soils from several areas in China

This paper gives the first data on^239,240Pu and²⁴¹Am in Chinese soils. Surface soil samples with a set of 0–5 cm and 5–20 cm depth were collected from Beijing, Taiyuan, Shijiazhuang and Jinang of China in 1990, and^239,240Pu,²⁴¹Am and¹³⁷Cs, including naturally occurring radionuclides, in these samples were measured to evaluate their present levels and distributions. From these results, the average accumulated depositions were estimated roughly to be 24±13 MBq/km² for^239,240Pu, 10±5 MBq/km² for²⁴¹Am and 1.2±0.7 GBq/km² for¹³⁷Cs. The activity ratios of^239,240Pu/¹³⁷Cs and²⁴¹Am/^239,240Pu ranged from 0.016 to 0.026 with a mean value of 0.020±0.004 and 0.35 to 0.49 with a mean value of 0.43±0.05, respectively.     

Assessment of intake of a complex radionuclide bearing dust formed at a nuclear power plant

The aim of this work was to provide an experimental basis for assessing intakes of an industrial actinide-bearing dust from measurements of⁶⁰Co and¹³⁷Cs in the body or urine. Whilst these radionuclides comprised 72% and 19% of the radioactivity present, greater than 90% of the committed effective dose will result from the low concentrations of the actinides present, 0.4%. To assess the dose coefficient for the dust and predict the biokinetics of⁶⁰Co and¹³⁷Cs in workers, absorption parameters for transfer from lungs to blood obtained from an animal study were combined with information on particle deposition and clearance from the ICRP human respiratory tract model and with tissue distribution and excretion data from the most recent systemic models. All other radionuclides were assumed to have Type M absorption characteristics. The dose coefficient for the dust, 1.29·10^–7 Sv·Bq^–1 was estimated to contain 113 kBq⁶⁰Co, 29 kBq¹³⁷Cs and 0.64 kBq of the actinides. The predicted retention and excretion characteristics of⁶⁰Co and¹³⁷Cs in workers after acute or chronic exposure to the dust suggested that measurements of these radionuclides in the body or urine could detect intakes equivalent to a few percent of an annual dose limit of 20 mSv·y^–1.     

Removal of226Ra(II) from uranium mining and processing effluents

The activity of¹³⁷Cs was determined in mosses and their surrounding soils in three Venezuelan cloud forests. The concentration of¹³⁷Cs in both the mosses and their respective soils were correlated with elevation (m.a.s.l.). This relationship was the result of the cloud forest effect, no direct deposition by condensation below the base of the clouds and increasing deposition of¹³⁷Cs with the density of the clouds. The ratio of the activity of¹³⁷Cs in the mosses to their surrounding soils was in general the same for sites near the top of the mountains, but the ratio at the Altos de pipe location was 3.5 times higher than that of the La Sierra mountain. This was explained by the difference in the water content of the surface and the top soil layer. It was concluded that the¹³⁷Cs measured in the mosses was from the soil effect rather than new deposition of¹³⁷Cs in the last three years.     

Fall out and radionuclide analysis on the Pratas Island in South China Sea

The radionuclide concentration in environmental samples and radiation level on Pratas Island are measured prior to the commercial operation of Da-Ya Bay Nuclear Power Plant nearby. Except for some minute amount of⁶⁰Co and¹⁵⁷Cs, radiation background is mainly from naturally occurring radionuclides. Automatic radiation surveillance and a routine sampling program on Pratas Island are essential to provide early warning for Taiwan in case of nuclear emergency.     

The distribution and behaviour of artificial radionuclides in sediments of the north Wales coast,U.K.

The distribution of¹³⁴Cs,¹³⁷Cs and²¹⁴Am in surface and core sediments from areas in north Wales has been investigated. Coastal sites show a predominance of Sellafield-derived material for all three radionuclides whereas estuarine sites show an increased proportion of Chemobyl-derived caesium present. By the use of the¹³⁴Cs/¹³⁷Cs ratio, a mean proportion of Chemobyl-derived¹³⁷Cs in surface sediments collected in 1991 fell from 34% at an estuarine site to 11% at a coastal site. In deeper sections of cores representing sedimentation dates near the Chemobyl accident, up to 90% of¹³⁷Cs at the estuarine site and 26% at the coastal site can be attributed to Chemobyl. By using the position of the Chemobyl¹³⁴Cs and¹³⁷Cs peak in the cores, sedimentation rates of 0.7 mm·a^–1 were calculated.     

Occurrence of natural radionuclides and fallout cesium-137 in dry-season agricultural land of South Western Nigeria

The radioactivity of the Opa river — irrigated farmlands in the south western Nigeria was determined using an HpGe based, low-level passive gamma-counting system. With the exception of two isotopes, the main radionuclides analysed in the sample were the progenies of²³⁸U and²³²Th. The other two isotopes were the naturally occurring⁴⁰K and the anthropogenic¹³⁷Cs. The result obtained showed elevated levels of radioactivity from all detected radionuclides compared to the published data for this area. Enhanced levels of naturally occurring radionuclides is attributed to the use of phosphatic fertilizers for dry season vegetable cultivation along this river banks. The presence of the fission product¹³⁷Cs could be traced to the fallouts occasioned by the various French nuclear tests in the Sahara desert, and probably, some effect of the more recent nuclear reactor accident at Chernobyl in 1986.     

Distribution of3H,137Cs and239,240Pu in the surface seawater around Korea

The concentrations of³H,¹³⁷Cs and^239,240Pu were determined in surface seawaters collected at 21 sampling stations around Korea from October of 1994 to May of 1995. The results were consistent with the past data observed in the North Pacific. The concentrations of³H and¹³⁷Cs did not show much difference no matter where the samples were taken. Due to the limited distribution of sampling points, no systematic change in³H and¹³⁷Cs levels with latitude was observed. On the other hand,^239,240Pu concentration in the East Sea (Japan Sea) was somewhat higher than that in the South and the Yellow Seas, although the data on^239,240Pu concentration were not enough to explain the reason. The activity ratios of^239,240Pu/¹³⁷Cs in surface seawater ranged from 0.13% to 0.44% with a mean of 0.25±0.08%. The activity ratios were lower than those of the global fall-out level, 1.1%. This result presumably arose from the different behavior of the two radionuclides in seawater.     

Determination of137Cs and134Cs in air samples collected near Belgrade /Yugoslavia/ following the Chernobyl accident

This paper presents the results of measurements of¹³⁷Cs and¹³⁴Cs content in air sampled during May 1986. Maximum concentrations:¹³⁷Cs 2.94±0.01 Bq m^–3 and¹³⁴Cs 1.38±0.01 Bq m^–3 were registered on May 3. Several other long lived radionuclides having -energies in the region 33 keV to 1365 keV were registered in the same samples two years later. The results of measurements of the total -activity in air for the same period are also presented.     

Determination of long-lived fission products and actinides in Savannah River Site HLW sludge and glass for waste acceptance

Savannah River Site (SRS) is immobilizing the radioactive, high-level waste sludge in Tank 51 into a borosilicate glass for disposal in a geologic repository. A requirement for repository aceeptance is that SRS report the concentrations of certain fission product and actinide radionuclides in the glass. This paper presents measurements of many of these concentrations in both Tank 51 sludge and the final glass. The radionuclides were measured by inductively coupled plasma mass spectrometry and α, β, and γ counting methods. Examples of the radionuclides are⁹⁰Sr,¹³⁷Cs,²³⁸U and,²³⁹Pu. Concentrations in the glass are 3.1 times lower due to dilution of the sludge with a nonradio-active glass forming frit in the vitrification process. Results also indicated that in both the sludge and glass the relative concentrations of the long lived fission products insoluble in caustic are in proportion to their yields from the fission of²³⁵U waste in the SRS reactors. This allowed the calculation of a fission yield scaling factor. This factor in addition to the sludge dilution factor can be used to estimate concentrations of waste acceptance radionuclides that cannot be measured in the glass. Examples of these radionuclides are⁷⁹Se,⁹³Zr, and¹⁰⁷Pd.     

131I and137Cs in the environment following the chernobyl reactor accident

The measured¹³¹I and¹³⁷Cs radioactivity in air, on the ground, and in milk at different places throughout the world were compared. It was found that the measured radioactivity can be explained assuming that the radioactive material released during the Chernobyl accident was transported primarily in two segments. The first part was transported at low altitudes, contaminated areas around Chernobyl and extended up to 2000–3000 km. The second part was injected into the troposphere. The radionuclides carried at high altitudes by the west-to-east winds traveled over continental Asia, Japan, Pacific Ocean, and North America. The time integrated radioactivity concentrations in nearground air particulates, the integral ground deposition densities and milk concentrations can be described by an exponential decrease as a function of the distance from Chernobyl. The intercept (values near the damaged reactor) and the slopes (describing dispersion conditions) were calculated. The deposition velocities for¹³¹I and¹³⁷Cs transported with the two altitude air masses are given.This work was supported in part by the Computer Center of the University of Maryland.