Chernobyl Reactor Research Articles

Thyroid diseases around Chernobyl: from autoimmune diseases to malignant tumors

Both an increased incidence of thyroid carcinoma mainly of the papillary histotype and to a lesser extent, of autoimmune phenomena have been observed, several years after external irradiation to the head and the neck, in subjects treated for various non-thyroidal disorders, in atomic bomb survivors in Japan, and in residents of the Marshall Island exposed to radiation during the testing of hydrogen bombs. More recently, the exposure to radioactive fallout as a result of the Chernobyl nuclear reactor accident has clearly confirmed the causal association of radiation exposure and the development of thyroid autoimmune phenomena in the population exposed to radiation. This article will review the most significant features of thyroid diseases associated with the post-Chernobyl radioactive contamination.

Gene rearrangements in thyroid carcinomas after irradiation during childhood: lessons from the Chernobyl reactor accident

Papillary thyroid carcinomas (PTC) developed with a high incidence in children and young adults who had been exposed to radioactive fallout in contaminated regions of Belarus after the Chernobyl reactor accident. They are informative for a molecular genetic analysis of radiation-induced PTC. In contrast to spontaneous PTC, a high prevalence of gene aberrations was found with rearrangements of the receptor tyrosine kinase gene RET in the majority of cases and a few NTRK1 rearrangements. In the rearranged form of RET, the transmembrane and extracellular parts are replaced by regulatory units of other genes. Among the fused genes, ELE1 ( ARA70) is most prevalent in PTC at short latency periods after irradiation, H4 gene fusions prevail in later-occurring PTC. Both types of rearrangement, PTC3 and PTC1, respectively, are formed by intrachromosomal inversions on chromosome 10. Analysing ELE1/ RET chimeric genes, we found radiation-induced DNA breakpoints localized exactly at or in close vicinity to topoisomerase I binding sites indicating a role for this enzyme in the formation of DNA breaks after irradiation. Breakpoints are distributed in the affected introns of both genes without significant clustering. They do not contain larger deletions of insertions. Short regions of sequence homology and short direct or inverted repeats were observed at the breakpoints suggesting microhomology-mediated DNA end joining as a mechanism in the fusion process. In addition to PTC1 and PTC3, we and others described several rare novel types of RET rearrangement, all formed by interchromosomal translocations, with parts of RIα, GOLGA5, HTIF, RFG7, RFG8, KTN1, and ELKS fused at the 5' end of the RET tyrosine kinase domain. These gene fusions appear to have in common an uncoupling of the RET tyrosine kinase from its physiological control due to an inherent dimerization potential. This may lead to constitutive, ligand-independent activation of RET tyrosine kinase in thyrocytes lacking this activity under normal conditions, and subsequent clonal expansion of the affected cells. It is evident from our comparative study on a large number of PTC with ELE1/ RET and H4/ RET rearrangements after irradiation that the type of the RET-fused gene determines the tumor phenotype and may be decisive also for the clinical course of radiation-induced PTC.

Reconstruction of thyroid dose after the Chernobyl accident

The main stages of the work conducted and the results of thyroid dose reconstruction for the Belarusian residents are presented in the paper. The problems relating to the systematic errors which occurred during in vivo monitoring of 131I-thyroid content are considered. The importance of using the most adequate model of thyroid dose formation has been justified in order to account for systematic errors. The main statements of the modified semiempirical model of thyroid dose formation have been described. The problem regarding possible production of fresh fission products (including short-lived radioiodines) at the time of the explosion of the Chernobyl reactor is presented. The main materials related to presentation of the results of our investigations on thyroid dose reconstruction in Belarus were in the literature, for example, Refs. [1–4]. This is the reason for which they are described here in a shortened view. The main attention is paid to the questions, which are actual for the time being, and those questions are likely to be actual in the future. Because of their importance those questions are being discussed in the framework of BelAm and UkrAm thyroid cohort projects as well as of the other projects.

137Cs dating of lacustrine sediments and human impacts on Dalian Lake, Qinghai Province, China

137Cs and grain-size analyses indicate the total amounts of 137Cs deposited by wind and water in the Dalian Lake of Gonghe Basin, Qinghai Province. The vertical profile of 137Cs in the lacustrine sediments shows three 137Cs activity peaks and one trough: the main peak corresponds to the global 137Cs fallout in 1963; the two secondary peaks correspond to the leakage of the Chernobyl reactor in 1986 and complete desiccation of the lake in 1994. The trough corresponds to aeolian deposition caused by extensive reclamation of farmland in late 1980s and early 1990s. The 137Cs dating was used to evaluate sedimentation rates in Dalian Lake since 1963. They are divided into three periods: two with slow deposition (1963–1986 and 1994–1998), and one with rapid deposition (1986–1994). 137Cs seems to have the same potential for indicating environmental changes and human interference in the arid and semiarid regions as in humid regions.

Regional distribution of Chernobyl-derived plutonium deposition in Finland

The Chernobyl nuclear power plant accident in April 1986 caused a widely spread plume of radionuclides containing, amongst other materials, plutonium isotopes. The regional deposition of these nuclides in Finland has been assessed, based on samples of lichen, peat, precipitation, surface soil and grass. Unlike the deposition of transuranium elements from the weapons tests in the 1950"s and the 1960"s, the deposition in Finland from the Chernobyl accident was very unevenly distributed. Even then, the Chernobyl-derived deposition of 239,240Pu in the most contaminated regions of Finland was only around 10% of the global fallout from weapons tests. The total amount of 239,240Pu deposited in Finland was 1.1011 Bq (»25 g), i.e., approximately half of a percent of the activity deposited in the 1950"s and the 1960"s. In addition to the alpha-emitting Pu isotopes, the Chernobyl plume also contained a significant amount of the beta-emitting 241Pu, which is the precursor of the long-lived alpha-emitter 241Am. The highest plutonium deposition values were found in a relatively narrow swath from the southwestern coast of Finland northeastwards across the country. This is related to the calculated route of the air parcel trajectory associated with the initial explosion of the Chernobyl reactor. The high deposition values found in the northeastern part of the plume route over Finland can be attributed to the simultaneous occurrence of precipitation. The relatively high plutonium deposition in the southwestern part of Finland occurred, however, without concurrent precipitation. This indicates that the plutonium was at least partly associated with relatively large particles having a substantial deposition velocity due to gravitational setting

Children of Chernobyl cleaners at risk

Children of the people who cleaned up the Chernobyl reactor after a core meltdown in 1986 (liquidators) are 600% more likely to have a genetic mutation compared with siblings born before the nuclear accident, according to research published by the …

Cambial history of Scots pine trees ( Pinus Sylvestris) prior and after the Chernobyl accident as encoded in the xylem

Studies were carried out on wood samples collected in October 1997 from breast height of Scots pine trees ( Pinus sylvestris) from site located 5 km south from the Chernobyl nuclear power plant. The radioactive contamination at the site was 3.7×10 5 kBq m − 2 . These samples of secondary wood were used as an archive of information about the dynamics of a meristematic tissue cambium affected by ionising radiation from the Chernobyl reactor accident. The results show that frequency of the cambial cells events like anticlinal divisions, intrusive growth and cells elimination, was after the Chernobyl accident, about three times higher in comparison to preceding years. The most interesting finding was that after irradiation the length of tracheids increased. This increase is interpreted as an effect of intracambial competition among cells in the initial layer.

Very high mutation rate in offspring of Chernobyl accident liquidators.

Exposure to ionizing radiation has long been suspected to increase mutation load in humans. Nevertheless, such events as atomic bombing seem not to have yielded significant genetic defects. The Chernobyl accident created a different, long-term exposure to radiation. Clean-up teams (or 'liquidators') of the Chernobyl reactor are among those who received the highest doses, presumably in some combination of acute and chronic forms. In this study, children born to liquidator families (currently either in the Ukraine or Israel) conceived after (CA) parental exposure to radiation were screened for the appearance of new fragments using multi-site DNA fingerprinting. Their sibs conceived before (CB) exposure served as critical internal controls, in addition to external controls (non-exposed families). An unexpectedly high (sevenfold) increase in the number of new bands in CA individuals compared with the level seen in controls was recorded. A strong tendency for the number of new bands to decrease with elapsed time between exposure and offspring conception was established for the Ukrainian families. These results indicate that low doses of radiation can induce multiple changes in human germline DNA.

Gene rearrangements in radiation-induced thyroid carcinogenesis.

Radiation is an accepted risk factor for thyroid carcinogenesis in children. Recent observations in large cohorts of children and young adults who developed papillary thyroid carcinomas (PTC) related to accidental radiation exposure after the Chernobyl reactor accident revealed typical genetic aberrations shedding light on genetic determinants and mechanisms of radiation-induced carcinogenesis. A molecular genetic analysis was performed on 191 post-Chernobyl PTC by RT-PCR, multiplex PCR, DNA sequencing, and in some cases 5'RACE. Determination of point mutations was by means of PCR and either allele-specific oligonucleotide hybridization or SSCP and DNA sequencing. In various sporadic thyroid tumor types of adults structural genetic aberrations have been found involving mutations of RAS (codon 12, 13, 61), p53 (exons 5 to 8), Gsalpha (codon 201 and 227), and, at a low prevalence, the receptor tyrosine kinases RET or NTRK1. In contrast, in radiation-induced PTC of children RET rearrangements are by far the most prevalent genetic aberrations. In these RET rearrangements, the transmembrane and extracellular domains of RET are lost, and are replaced by parts of other genes at the 5' end. These genes always contain coiled-coil domains with dimerization potential and lead to constitutive, ligand-independent activation of the ret tyrosine kinase domain at the 3' end of the fusion product. The most frequent radiation-induced RET gene fusions involve the ELE1 (ARA70) gene, a transcription coactivator of the androgen receptor (PTC3), and H4, a gene of unknown function (PTC1). Both rearrangements originate from DNA double strand breaks with repair by intrachromosomal balanced paracentric inversion and recombination by illegitimate DNA endjoining at small stretches of homologous nucleotide sequences and direct or inverted repeats, without significant breakpoint clusters in the involved introns. In addition, five different RET-fused genes, RIalpha, GOLGA5, HTIF, RFG7 and RFG8, have been detected leading to the PTC2, 5, 6, 7 and 8 types of RET rearrangements, respectively. Each fusion leads, in principle, to the same effect: The ret tyrosine kinase is uncoupled from its stringent physiological regulation by replacement of its 5' end and is aberrantly activated by the 5' parts of fused genes in thyrocytes that do not normally express ret tyrosine kinase. Ectopic ret expression, clonal expansion and early invasion are peculiar to the affected cells. The RET-fused gene is obviously decisive for modulating tumor development: ELE1/RET rearrangements lead to most rapid tumor progression and are related to the solid variant of PTC, in contrast to H4/RET rearrangements connected with papillary or follicular variants of PTC. Typical genetic aberrations are produced by radioiodine uptake in the juvenile thyroid gland. They act as determinants of phenotype, biology, and clinical course of radiation-induced papillary thyroid carcinomas.

RET Rearrangements in Radiation-Induced Papillary Thyroid Carcinomas: High Prevalence of Topoisomerase I Sites at Breakpoints and Microhomology-Mediated End Joining in ELE1 and RET Chimeric Genes

Children exposed to radioactive iodine after the Chernobyl reactor accident frequently developed papillary thyroid carcinomas (PTC). The predominant molecular lesions in these tumors are rearrangements of the RET receptor tyrosine kinase gene. Various types of RET rearrangements have been described. More than 90% of PTC with RET rearrangement exhibit a PTC1 or PTC3 type of rearrangement with an inversion of the H4 or ELE1 gene, respectively, on chromosome 10. To obtain closer insight into the mechanisms underlying PTC3 inversions, we analyzed the genomic breakpoints of 22 reciprocal and 4 nonreciprocal ELE1 and RET rearrangements in 26 post-Chernobyl tumor samples. In contrast to previous assumptions, an accumulation of breakpoints at the two Alu elements in the ELE1 sequence was not observed. Instead, breakpoints are distributed in the affected introns of both genes without significant clustering. When compared to the corresponding wildtype sequences, the majority of breakpoints (92%) do not contain larger deletions or insertions. Most remarkably, at least one topoisomerase I site was found exactly at or in close vicinity to all breakpoints, indicating a potential role for this enzyme in the formation of DNA strand breaks and/or ELE1 and RET inversions. The presence of short regions of sequence homology (microhomologies) and short direct and inverted repeats at the majority of breakpoints furthermore indicates a nonhomologous DNA end-joining mechanism in the formation of chimeric ELE1/Ret and Ret/ELE1 genes.

137Cs tracing of lacustrine sediments in the Dalian Lake, Qinghai Province, China

Based upon the analysis of137Cs and grain-size parameters, the total amounts of137Cs deposition by wind and water in the Dalian Lake of Gonghe Basin, Qinghai Province are defined. The vertical profile of Cs in the lacustrine sediments exhibits three137Cs activity maxima and one minimum. The major maximum corresponds to the global137Cs fallout in 1963; the two secondary maxima correspond to the leakage of the Chernobyl reactor in 1986 and complete desiccation of the lake in 1994, respectively. The minimum corresponds to aeolian deposition caused by extensive reclamation in the late 1980s and early 1990s. The137Cs data set was used to evaluate average sedimentation rate of the Dalian Lake since 1963. The deposition was stable in 1963–1986 and 1994–1998, and it was rapid during 1986–1994. This preliminary study reveals that137Cs has the same potential to trace environmental changes introduce by human interference in arid/semiarid regions as in humid regions.

Soil contamination with 90Sr in the near zone of the Chernobyl accident

Representative large-scale soil sampling on a regular grid of step width about 1 km was carried out for the first time in the near zone of the Chernobyl accident (radius 36 km). An integrated map of terrestrial 90Sr contamination density in the 30 km exclusion zone (scale 1 : 200,000) has been created from the analysed samples. Maps of the main agrochemical characteristics of the soils, which determine the fuel particle dissolution rates and the contamination of vegetation, were produced. The total contents of 90Sr on the ground surface of the 30 km zone in Ukraine (without the reactor site and the radioactive waste storages) was about 810 TBq (8.1×10 +14 Bq) in 1997, which corresponds to 0.4–0.5% of the Chernobyl reactor inventory at the time of the accident. This assessment is 3–4 times lower than previous estimates.

Nuclear Power Requires Strong Governmental Support to Restore Confidence and Build New Capacity

Nuclear power has been neglected and has attracted too much bad publicity eg. The UK's Sellafield debacle. This has allowed a minority of anti-nuclear campaigners to further undermine the nuclear power industry. Governments should re-evaluate their energy policies and consider if it is in national interests to continue to subsidise underground coal mining and renewable energy sources whilst neglecting nuclear power. It is encouraging that the last Chernobyl reactor in the Ukraine has been closed, Sweden has delayed the phasing out of nuclear power and France has reorganised its nuclear sector to improve profitability, transparency and PR. Optimists hope that France will soon commission work which will lead to replacement of its 58 nuclear reactors. Extracts from papers given at the Uranium Institute Symposium 2000 are included which provide nuclear industry expert views. These views are supplemented by the latest US DOE/EIA projections to 2020.

Source-related Characteristics of Radioactive Particles: A Review

A significant fraction of radionuclides released by nuclear events, for instance nuclear weapons tests, nuclear reactor accidents, and fires involving nuclear installations is associated with particles. Furthermore, effluents from nuclear reactors and reprocessing plants under normal operating conditions contain radionuclides in particulate and colloidal form. Radioactive particles are also observed in the vicinity of radioactive waste dumped at sea. Following nuclear tests, the particle composition and characteristics were found to be device and shot dependent. Following high temperature accident scenarios (e.g. Chernobyl), fuel particles were released having a composition of refractory elements reflecting burnup. However, the release condition (explosion, fire) influenced the crystallographic structures and oxidation states of uranium in the fuel particles. Following low temperatures atmospheric releases (e.g. Windscale, early 1950s), fuel particle structures were significantly different from those released from the Chernobyl reactor. This paper focuses on source and release-dependent characteristics of radioactive particles, which in turn influence the behaviour of the associated radionuclides in the environment.

Cesium separation from contaminated milk using magnetic particles containing crystalline silicotitanates

The Chernobyl nuclear reactor disaster in 1986 contaminated vast regions of prime grazing land. Subsequently, milk produced in the region has been contaminated with small amounts of the long-lived fission product cesium-137, and the Ukraine is seeking to deploy a simple separation process that will remove the Cs and preserve the nutritional value of the milk. Tiny magnetic particles containing crystalline silicotitanates (CST) have been manufactured and tested to this end. The results show that partitioning efficiency is optimized with low ratios of particle mass to volume. To achieve 90% Cs decontamination in a single-stage process, <3 g of magnetic CST per l milk is sufficient with a 30-min mixing time. A two-stage process would utilize <0.4 g/l per stage. The modeling of the magnetic CST system described herein can be achieved rather simply which is important for deployment in the affected Ukraine region.

Radioactivity in tobacco leaves

The radioactivity in tobacco leaves collected from 15 different regions of Greece before cigarette production was studied in order to find any association between the uptake of the naturally occurring radionuclides and the isotopes of cesium of Chernobyl origin. The activities of the isotopes of radium, 226 Ra and 228 Ra , in the tobacco leaves reflected their origin from the soil by root uptake rather than from fertilizers used in the tobacco cultivation. Lead-210 originated from the air and was deposited onto the tobacco leaves and trapped by the trichomes. Potassium-40 in the tobacco leaves was due to root uptake either from soil or from fertilizer. The isotopes of cesium, 137 Cs and 134 Cs , in the tobacco leaves were due to root uptake and not due to deposition onto the leaf foliage as they still remained in soil four years after the Chernobyl reactor accident but were absent from the atmosphere in rain washout (precipitation) and gravitational settling.

Whole-body Measurement and Quality Assurance

Some of the quality assurance tasks of whole-body counting are specific to that method of measurement, whereas others are similar to those of gamma spectrometric sample measurements. Quality assurance in whole-body measurement and the associated calculation of internal doses is a complex matter. The uncertainty in the measurement geometry between the radiation source and the detector is unavoidable when measuring humans. Quality assurance includes quality control with procedure and protocol descriptions, detector calibrations, instrument control, documentation of measurement results and evaluation internally or by outside persons. This evaluation also involves regularly repeated comparative measurements. An intercomparison study in the Nordic countries was carried out using a phantom that corresponded to a person weighing 62 kg. The radionuclides used were 60 Co, 137 Cs and 40 K. The phantom was circulated to seventeen laboratories. The results agreed well with the reference values. The results from this project showed that the preparedness for performing body and organ measurements in emergency situations has improved greatly since the Chernobyl reactor accident.

Concentrations of 239Pu and 240Pu and Their Isotopic Ratios Determined by ICP-MS in Soils Collected from the Chernobyl 30-km Zone

Soil samples collected from three forest sites within the 30-km zone around the Chernobyl reactor were analyzed for 239Pu and 240Pu by ICP-MS. The average 240Pu/239Pu atom ratio in contaminated surface soil samples, values of which are scarce in the literature, was 0.408. There were almost no differences in the 240Pu/239Pu ratios between the individual samples analyzed, although the 239+240Pu levels varied very widely (i.e. from 6.3 to 1430 Bq kg-1 dry weight) depending on the distance from the reactor and on the soil layers investigated. This result corresponded to area-related activities for 239+240Pu between 1.1 kBq m-2 and 13.3 kBq m-2. It was estimated that about half of the Pu migrated from the organic layers to the underlying mineral layers. The 240Pu/239Pu ratio observed in the Chernobyl area was much higher than that attributed to weapons fallout (ca. 0.18). The high ratio was related to the high burn-up grade of the reactor fuel. The 240Pu/239Pu ratio observed might be used as a “fingerprint” in identifying the distribution of Chernobyl-derived Pu in the environment and in distinguishing it from other sources, e.g. global fallout. Relationships between the concentrations of Pu and those of 137Cs, 60Co, and 125Sb were also discussed.

Separation of Tc-99 in soil and plant samples collected around the Chernobyl reactor using a Tc-selective chromatographic resin and determination of the nuclide by ICP-MS

Technetium (Tc) is known to have high mobility in a soil–water system and also high bioavailability for plants, because the most stable form of Tc in natural surface environment is thought to be TcO−4 which is highly soluble. The chemical form of Tc, however, changes with environmental conditions. Thus, it is necessary, for realistic assessment, to obtain transfer parameters, such as transfer factors, under natural conditions. However, it is difficult to obtain these parameters using global fallout 99Tc in actual fields due to its low concentration. In this study, 99Tc concentrations in surface soil and plant leaf samples collected from forest sites within the 30-km zone around the Chernobyl reactor were measured for the first time. In the case of soil samples, a simple and rapid analytical method for determination of 99Tc is used which consists of volatilizing and trapping Tc in a combustion apparatus, purifying the Tc with an extraction chromatographic resin, and measuring it by inductively coupled plasma mass spectrometry (ICP-MS). For plant samples, a wet digestion method in combination with the resin is applied and the 99Tc is measured by ICP-MS. Concentrations of 99Tc in organic soil samples and leaves of strawberry (Fragaria vesca) range from 1.1–14.8 Bq kg−1 dry weight and 0.2–6.0 Bq kg−1 dry weight, respectively. Our results indicate that soil-to-plant transfer factors for Tc are similar to those for Cs.

Health status and internal radiocontamination assessment in children exposed to the fallout of the Chernobyl accident.

The Chernobyl fallout caused release of radioisotope contaminants in a very large area that includes Belarus, the Ukraine, and the Russian Federation. In this study, the authors monitored the health status and level of internal contamination in 422 children who resided in the aforementioned areas and who were < or = 10 y of age at the time of the accident. The children came to Italy for a 1-mo period between 1991 and 1992. During this time, the children underwent pediatric checkups and biochemical, immunological, and thyroid analyses. All children underwent whole-body counter measurements, and urine radiotoxicological analysis was performed for 224 of them. The 24 children evacuated from Pripiat, a village very close to the Chernobyl reactor site, were selected for cytogenetic analysis. All of these children continue to have a detectable internal contamination of caesium radioisotopes. This condition is likely the result of ground and foodstuff contamination in the various areas. The children did not evidence overt pathologies related to ionizing radiation. However, minor alterations in immunological and thyroid parameters were observed in the group of the evacuated children. Traditional cytogenetic dosimetry was not possible, but the occurrence of acentric fragments was observed-indicating a persistent effect of continuous exposure to low doses of radiation.