PROPOSALS FOR THE ESTABLISHMENT OF NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR RADIOGRAPHY FOR ADULT PATIENTS BASED ON REGIONAL DOSE SURVEYS IN RUSSIAN FEDERATION.

In 2009-2014, dose surveys aimed to collect adult patient data and parameters of most common radiographic examinations were performed in six Russian regions. Typical patient doses were estimated for the selected examinations both in entrance surface dose and in effective dose. 75%-percentiles of typical patient effective dose distributions were proposed as preliminary regional diagnostic reference levels (DRLs) for radiography. Differences between the 75%-percentiles of regional typical patient dose distributions did not exceed 30-50% for the examinations with standardized clinical protocols (skull, chest and thoracic spine) and a factor of 1.5 for other examinations. Two different approaches for establishing national DRLs were evaluated: as a 75%-percentile of a pooled regional sample of patient typical doses (pooled method) and as a median of 75%-percentiles of regional typical patient dose distributions (median method). Differences between pooled and median methods for effective dose did not exceed 20%. It was proposed to establish Russian national DRLs in effective dose using a pooled method. In addition, the local authorities were granted an opportunity to establish regional DRLs if the local radiological practice and typical patient dose distributions are significantly different.

Effective dose and risks from medical X-ray procedures.

The radiation risks from a range of medical x-ray examinations (radiography, fluoroscopy, and computed tomography) were assessed as a function of the age and sex of the patient using risk models described in Publication 103 (ICRP, 2007) and UNSCEAR (2006, Annex A). Such estimates of risk based on typical organ doses were compared with those derived from effective doses using the International Commission on Radiological Protection's nominal risk coefficients. Methodologically similar but not identical dose and risk calculations were performed independently at the Institute of Radiation Hygiene (Russia) and the Health Protection Agency (UK), and led to similar conclusions. The radiogenic risk of stochastic health effects following various x-ray procedures varied significantly with the patient's age and sex, but to differing degrees depending on which body organs were irradiated. In general, the risks of radiation-induced stochastic health effects in children are estimated to be higher (by a factor of ≤ 4) than in adults, and risks in senior patients are lower by a factor of ≥ 10 relative to younger people. If risks are assessed on the basis of effective dose, they are underestimated for children of both sexes by a factor of ≤ 4. This approach overestimates risks by a factor of ≤ 3 for adults and about an order of magnitude for senior patients. The significant sex and age dependence of radiogenic risk for different cancer types is an important consideration for radiologists when planning x-ray examinations. Whereas effective dose was not intended to provide a measure of risk associated with such examinations, it may be sufficient to make simple adjustments to the nominal risk per unit effective dose to account for age and sex differences.

On protecting the inexperienced reader from Chernobyl myths.

The health and environmental consequences of the Chernobyl accident continue to attract the attention of experts, decision-makers and the general public, and now these consequences have been given added relevance by the similar accident in 2011 at the Fukushima-1 nuclear power plant (NPP) in Japan. Expert analysis of radiation levels and effects has been conducted by international bodies--UNSCEAR in 2008 and the Chernobyl Forum during 2003-5. At the same time, three Russian and Belarusian scientists, Yablokov, Nesterenko and Nesterenko (2009 Chernobyl. Consequences of the Catastrophe for People and the Environment (New York: Annals of the New York Academy of Sciences)) published both in Russian and English a substantial review of the consequences of Chernobyl based mostly on Russian-language papers. In this book, they suggested a departure from analytical epidemiological studies in favour of ecological ones. This erroneous approach resulted in the overestimation of the number of accident victims by more than 800 000 deaths during 1987-2004. This paper investigates the mistakes in methodology made by Yablokov et al and concludes that these errors led to a clear exaggeration of radiation-induced health effects. Should similar mistakes be made following the 2011 accident at Fukushima-1 NPP this could lead quite unnecessarily to a panic reaction by the public about possible health effects and to erroneous decisions by the authorities in Japan.

Contribution of internal exposures to the radiological consequences of the Chernobyl accident.

The main pathways leading to exposure of members of the general public due to the Chernobyl accident were external exposure from radionuclides deposited on the ground and ingestion of contaminated terrestrial food products. The collective dose to the thyroid was nearly 1.5 million man Gy in Belarus, Russia and Ukraine with nearly half received by children and adolescents. The collective effective dose received in 1986-2005 by approximately five million residents living in the affected areas of the three countries was approximately 50,000 man Sv with approximately 40% from ingestion. That contribution might have been larger if countermeasures had not been applied. The main radionuclide contributing to both external and internal effective dose is 137Cs with smaller contributions of 134Cs and 90Sr and negligible contribution of transuranic elements. The major demonstrated radiation-caused health effect of the Chernobyl accident has been an elevated incidence of thyroid cancer in children.

The Chernobyl Forum: major findings and recommendations.

The accident at the Chernobyl NPP in 1986 was the most severe in the history of the nuclear industry, causing a huge release of radionuclides over large areas of Europe. The recently completed Chernobyl Forum concluded that after a number of years, along with reduction of radiation levels and accumulation of humanitarian consequences, severe social and economic depression of the affected regions and associated psychological problems of the general public and the workers had become the most significant problem to be addressed by the authorities. The majority of the affected land is now safe for life and economic activities. However, in the Chernobyl Exclusion Zone and in some limited areas of Belarus, Russia and Ukraine some restrictions on land-use should be retained for decades to come. Most of the 600,000 emergency and recovery operation workers and five million residents of the contaminated areas in Belarus, Russia and Ukraine received relatively minor radiation doses which are comparable with the natural background levels. Apart from the dramatic increase in thyroid cancer incidence among those exposed at a young age and some increase of leukaemia and solid cancer in most exposed workers, there is no clearly demonstrated increase in the somatic diseases due to radiation.

Twenty years' application of agricultural countermeasures following the Chernobyl accident: lessons learned.

The accident at the Chernobyl NPP (nuclear power plant) was the most serious ever to have occurred in the history of nuclear energy. The consumption of contaminated foodstuffs in affected areas was a significant source of irradiation for the population. A wide range of different countermeasures have been used to reduce exposure of people and to mitigate the consequences of the Chernobyl accident for agriculture in affected regions in Belarus, Russia and Ukraine. This paper for the first time summarises key data on countermeasure application over twenty years for all three countries and describes key lessons learnt from this experience.

Soil-dependent uptake of 137Cs by mushrooms: experimental study in the Chernobyl accident areas.

The influence of agrochemical properties of forest soils and growth conditions on 137Cs aggregated transfer factors from soil to different species of forest mushrooms have been analysed. Statistically significant correlations between 137Cs soil to mushroom aggregated transfer factors and agrochemical soil properties have been revealed. The experimental data show that 137Cs aggregated transfer factors depend on the mushroom's trophic group, biological family, genus and species. They also strongly depend on forest soil properties and their values can be estimated with the use of multiple regression equations constructed from agrochemical soil parameters which most closely correlate with the 137Cs transfer parameters for particular mushroom groups.

Model testing using data on 137Cs from Chernobyl fallout in the Iput River catchment area of Russia.

Data collected for 10 years following the Chernobyl accident in 1986 have provided a unique opportunity to test the reliability of computer models for contamination of terrestrial and aquatic environments. The Iput River scenario was used by the Dose Reconstruction Working Group of the BIOMASS (Biosphere Modelling and Assessment Methods) programme. The test area was one of the most highly contaminated areas in Russia following the accident, with an average contamination density of 137Cs of 800,000 Bq m-2 and localized contamination up to 1,500,000 Bq m-2, and a variety of countermeasures that were implemented in the test area had to be considered in the modelling exercise. Difficulties encountered during the exercise included averaging of data to account for uneven contamination of the test area, simulating the downward migration and changes in bioavailability of 137Cs in soil, and modelling the effectiveness of countermeasures. The accuracy of model predictions is dependent at least in part on the experience and judgment of the participant in interpretation of input information, selection of parameter values, and treatment of uncertainties.

Lake fish as the main contributor of internal dose to lakeshore residents in the Chernobyl contaminated area.

Two field expeditions in 1996 studied 137Cs intake patterns and its content in the bodies of adult residents from the village Kozhany in the Bryansk region, Russia, located on the shore of a drainless peat lake in an area subjected to significant radioactive contamination after the 1986 Chernobyl accident. The 137Cs contents in lake water and fish were two orders of magnitude greater than in local rivers and flow-through lakes, 10 years after Chernobyl radioactive contamination, and remain stable. The 137Cs content in lake fish and a mixture of forest mushrooms was between approximately 10-20 kBq/kg, which exceeded the temporary Russian permissible levels for these products by a factor of 20-40. Consumption of lake fish gave the main contribution to internal doses (40-50%) for Kozhany village inhabitants Simple countermeasures, such as Prussian blue doses for dairy cows and pre-boiling mushrooms and fish before cooking, halved the 137Cs internal dose to inhabitants, even 10 years after the radioactive fallout.

131I content in the human thyroid estimated from direct measurements of the inhabitants of Russian areas contaminated due to the Chernobyl accident.

The method of processing and the results of measurements of 131I content in the thyroids of Russian people performed in May-June 1986 are presented. The contribution of radiation from Cs radionuclides in the human body was taken into account in the processing of measurement data with an SRP-68-01 device. The greatest individual 131I content was found in the thyroids of inhabitants of the Bryansk region, up to 250-350 kBq, and in the Tula and Orel regions, up to 100 kBq. The average 131I thyroid activity in the middle of May 1986 reached 80 kBq for inhabitants of some settlements in the Bryansk region, 5-8 kBq in the Tula region and 5 kBq in the Orel region.

External exposure of the population living in areas of Russia contaminated due to the Chernobyl accident.

An updated version of external dose modeling is presented with reference to the population in Russian areas contaminated due to the Chernobyl accident. An earlier version has been modified by applying a study time interval with a starting point immediately after radionuclide deposition (rather than 4 years after the accident as applied earlier) and by introducing an estimate of individual dose distributions. New input data to the model are the nuclide-specific composition of the deposit, additional data about migration of caesium in soil, time dependence of location factors and uncertainty distributions of all input parameters. Model results (i.e. effective dose-rates and accumulated effective doses) from external exposure for the rural and urban populations in contaminated areas of Russia during 100 years after the accident are presented. Radionuclide contributions to the dose during various time intervals after the accident have been estimated. The model has been validated by measurements of absorbed dose-rate in air during the first 30 days after the accident and by TLD measurements of individual external doses among inhabitants of contaminated rural settlements in the year 1993. Both the measurements and model show that the geometric mean of individual external doses is about 10% lower than the arithmetic mean and the upper bound of the 95% confidence range is larger by a factor of about 2.

Current contamination by 137Cs and 90Sr of the inhabited part of the Techa river basin in the Urals.

Previous discharges of radioactivity from the Mayak Production Association plant in the Urals have resulted in considerable radionuclide contamination of the Techa River, and consequent high radiation doses during the late 1940s and 1950s to residents of villages along the Techa river. The most contaminated villages close to the site were evacuated in the period 1954-1962. The objective of this recent study was to conduct a preliminary assessment of the current radioactive contamination of soil, vegetation and foodstuffs in the two remaining villages closest to the Mayak site, Muslyumovo and Brodokalmak. The highest contamination levels in soil were found in the floodplain at 5.5 MBq m(-2) for 137Cs and 1.0 MBq m(-2) for 90Sr. Radionuclide contamination in soil of the villages was much lower, but exceeded that expected from global fallout. Data from 1207 measurements of 137Cs in milk and 1180 for 90Sr in milk for the period 1992-1999 were collated. There was no change with time in the 90Sr or 137Cs activity concentration in milk over the measured period. There were significantly higher 137Cs activity concentrations in milk sampled during the housed winter period in Muslyumovo compared with the grazing summer period, but compared to that for Brodokalmak or for either settlement for 90Sr. The highest measured activity concentrations in food products of 137Cs and 90Sr were found in river fish, waterfowl, poultry and milk. The measured activity concentrations of 137Cs and 90Sr in some animal products were higher than that expected from soil and vegetation from fields and pasture in the villages (not including the floodplain) confirming that the highly contaminated floodplains are contributing to contamination of some animal products.

Assessment of current exposure levels in different population groups of the Kola Peninsula.

Activity concentrations of 137Cs and 90Sr in samples of vegetation and natural food products collected in the Kola Peninsula in 1998 and 1999 indicate a very slow decrease in contamination levels during the last decade, mainly due to the physical decay of the radionuclides. The activity concentrations of 137Cs in reindeer meat decreased with a half-life of about 9 years. 137Cs in lichen, moss and fungi is significantly higher than in natural vegetation (grasses) and agricultural plants (potatoes). The activity concentrations of 137Cs in reindeer meat were two orders of magnitude higher than those in locally produced beef and pork. Consumption of reindeer meat, fish, mushrooms and berries constituted the main contribution to the internal dose from 137Cs and 90Sr for reindeer-breeders in the Lovozero area. The estimated committed doses due to 137Cs intake in this group were about 10 microSv per month in summer 1998 and 15 microSv per month in winter, 1999. There was good agreement between internal dose estimates based on intake assessment and whole body measurements. The population of Umba settlement, which is not involved in reindeer breeding, received individual committed doses due to 137Cs intake of about 0.5 microSv per month, about a factor of 20 less than the reindeer-breeders in Lovozero. In this case, the main contribution to the internal dose of the general population came from consumption the of 137Cs in mushrooms and forest berries. The contribution of 90Sr to the internal dose varied from 1% to 5% in the different population groups studied.

Contribution of different foodstuffs to the internal exposure of rural inhabitants in Russia after the Chernobyl accident.

In a large village, Veprin of the Bryansk region of Russia contaminated with radionuclides as a result of the Chernobyl accident, 137Cs concentration in food products of agricultural produce and natural origin was regularly measured, local inhabitants were polled on the composition of their diet, and the 137Cs content in their bodies was measured at the same time. These results were used as the basis for calculation of annual effective doses of internal exposure to inhabitants and for reconstruction of the dose during the entire period after the accident (1986-1996). The efficiency of countermeasures performed for reduction of the internal dose was assessed. The internal dose in inhabitants during the 10 years after the accident was shown to be reduced by countermeasures by a factor of 2, namely down to 35 mSv instead of the expected 70 mSv. The dose of external gamma radiation during the same time period is close to the obtained dose of internal exposure. The presence of peat and water-meadow soils in the vicinity of this village that are characterised by high transfer factors for radionuclides from soil to vegetation causes a high contribution of internal exposure to the total dose of population exposure. The contribution of natural products to the internal dose increased from 6% in 1987 increased to 25% in 1996. The individual content of 137Cs in the body of inhabitants reliably correlates with consumption of milk in the initial period after the accident and with consumption of forest mushrooms in the subsequent period.

Environmental radioactivity, population exposure and related health risks in the east Baltic region.

The paper considers radioactive contamination of the east Baltic region, population exposures, and the risk of damage to human health. Principal sources include global fallout, the Chernobyl accident, and marine transport of radionuclides. A mean annual exposure of 2-3 mSv comes from environmental radioactivity. Main contributors are primarily radon and its decay products. The Chernobyl accident brought an additional dose of about 0.5 mSv in southern Finland and 1.4 mSv in the most contaminated districts of the Leningrad region, Russia. Both external and internal exposure via contaminated food contributed. Currently, significant long-term radiological consequences of the Chernobyl accident include persistent radioactive contamination of natural terrestrial (forest) and freshwater (oligotrophic lakes) ecosystems and food products. Radiation health risks are lung cancer among the general population from indoor exposure to radon, acute radiation syndrome from occupational exposure, thyroid cancer among children in heavily contaminated non-Baltic areas, and mutations among offspring of exposed parents.

Strategy for population protection and area rehabilitation in Russia in the remote period after the Chernobyl accident.

The report presents the history of the development of criteria for radiation and social protection of the Russian population residing in the areas contaminated with radionuclides after the Chernobyl accident, in the remote time periods after the accident. The tendencies for reduction of standards with time are shown, and their causes are analysed. It is noted that the optimization principle was not applied in the explicit form for population protection. The current radiation situation in the contaminated areas of Russia is described, and the future situation is forecast. Main pathways of external and internal population exposure are described. Modern possibilities for reduction of the population exposure dose are discussed. The authors propose promising criteria and methods for population protection and rehabilitation of contaminated areas in Russia.

Health impacts of large releases of radionuclides. Internal exposure of populations to long-lived radionuclides released into the environment.

This chapter discusses the events that led to the contamination of environments with the long-lived radionuclides of caesium, strontium and other elements, and to the internal exposure of populations living in contaminated areas. Among these events are radioactive releases into the river Techa from the Soviet nuclear weapons facility Mayak in 1949-1956, thermonuclear weapons tests in the 1950s and 1960s, the Kyshtim and Windscale accidents in 1957, and the Chernobyl and Tomsk-7 accidents in 1986 and 1993, respectively. Methods of environmental monitoring and individual internal dose monitoring of inhabitants are described. These are based on measuring the content of radionuclides not only in the air, drinking water and local food products, but also in humans using whole-body counters and analysing excreta and autopsy samples. The dynamics of internal exposure of people of different ages to radionuclides of caesium, strontium and plutonium from the environment are considered. Examples of radionuclide distributions in the environment, and of individual/collective internal doses and related medical effects are presented.

Tritium radiobiological effects in mammals: review of experiments of the last decade in Russia.

This review briefly describes techniques and basic results of experimental investigations in mice and rats on metabolism, dosimetry, and radiobiological effects of tritium oxide and some tritiated biogenic compounds (glucose, amino acids, and nucleosides) during the last 10 to 15 years in Russia. The content of water in tissue cells of mammals is shown to be 15 to 40% less than in whole tissue. The kinetics of tritium incorporation from oxide (HTO) and its retention in DNA of hemopoietic tissues were studied. The contribution of bound tritium to dose strongly depends on the chemical form of tritium and reaches 90% when labeled L-lysine is injected. Specific features of the action of HTO on hemopoietic tissue were investigated in tests of damage and repair of DNA, induction of chromosome aberrations in cells, content of nucleic acids, kinetics of cell populations, immunity parameters, carcinogenesis, decrease of life span, induction of dominant lethal mutations in germ cells in male mice, and reciprocal translocations in mouse spermatogonia. According to these tests, the radiobiological effects of tritium beta radiation in the form of oxide is 2 to 6 times higher than for gamma radiation of 137Cs. The frequency of dominant lethal mutations induced by labeled lysine, thymidine, and deoxycytidine is 3 to 12 times higher than those induced by equal HTO activity. The results of these investigations are used to standardize HTO and the various biogenic compounds of tritium, improve techniques of indirect dosimetry, provide medical aid to personnel, and estimate population risk.

[Radiobiological characteristics of tritium labeled lysine]. / Radiobiologicheskaia kharakteristika mechennogo tritiem lizina.

Experiments on mice and rats injected with tritium-labeled lysine have revealed that one day after injection about 80% of the label was retained in organs and tissues as tissue-bound tritium. Retention curves for tritium in the body were decomposed into two exponentials. The biological half-lives of tritium-labeled lysine in various tissues exceed half-lives of other tritiated amino acids and of tritiated water. The average dose in different tissues following injection of tritiated lysine exceeds that from equal quantity of tritium oxide (THO) by 1,5-8 times. Contribution of the tissue-bound tritium in dose is about 90%. Radiobiological experiments showed strong genetic and cytotoxic effects in male mice after injection of tritium-labeled lysine.