SOURCES AND EFFECTS OF IONIZING RADIATION : United Nations Scientific Committee on the Effects of Atomic Radiation UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes

NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

sources and effects of ionizing radiation

Multivalent ligands can function as inhibitors or effectors of biological processes. Potent inhibitory activity can arise from the high functional affinities of multivalent ligand-receptor interactions. Effector functions, however, are influenced not only by apparent affinities but also by alternate factors, including the ability of a ligand to cluster receptors. Little is known about the molecular features of a multivalent ligand that determine whether it will function as an inhibitor or effector. We envisioned that, by altering multivalent ligand architecture, ligands with preferences for different binding mechanisms would be generated. To this end, a series of 28 ligands possessing structural diversity was synthesized. This series provides the means to explore the effects of ligand architecture on the inhibition and clustering of a model protein, the lectin concanavalin A (Con A). The structural parameters that were varied include scaffold shape, size, valency, and density of binding elements. We found that ligands with certain architectures are effective inhibitors, but others mediate receptor clustering. Specifically, high molecular weight, polydisperse polyvalent ligands are effective inhibitors of Con A binding, whereas linear oligomeric ligands generated by the ring-opening metathesis polymerization have structural properties that favor clustering. The shape of a multivalent ligand also influences specific aspects of receptor clustering. These include the rate at which the receptor is clustered, the number of receptors in the clusters, and the average interreceptor distance. Our results indicate that the architecture of a multivalent ligand is a key parameter in determining its activity as an inhibitor or effector. Diversity-oriented syntheses of multivalent ligands coupled with effective assays that can be used to compare the contributions of different binding parameters may afford ligands that function by specific mechanisms.

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Influencing Receptor−Ligand Binding Mechanisms with Multivalent Ligand Architecture

The synthesis of novel well-defined alkyne side chain functional polymers featuring narrow molecular weight distributions (PDI = 1.09−1.17) by living radical polymerization is described. Grafting of protected and unprotected carbohydrates is achieved via either a C-6 or an anomeric azide (α or β) onto these polymers by Cu(I)-catalyzed “click chemistry”, providing a simple and efficient route to synthetic glycopolymers. The strategy provides an extremely powerful tool for the synthesis of libraries of materials that differ only in the nature of the sugar moiety presented on a well-defined polymer scaffold. A library of multivalent ligands were then prepared following a “coclicking” synthetic protocol, and the reactivity of these glycopolymers in the presence of concanavalin A and Ricinus communis agglutinin, model lectins able to selectively bind appropriate mannose and galactose derivatives, respectively, was assessed.

Synthesis of neoglycopolymers by a combination of "click chemistry" and living radical polymerization.

relationship was observed up to 1.5 – 2 Gy. The risk of radiation-related thyroid cancer was three times higher in iodine-defi cient areas (relative risk [RR]= 3.2, 95% CI = 1.9 to 5.5) than elsewhere. Administration of potassium iodide as a dietary supplement reduced this risk of radiation-related thyroid cancer by a factor of 3 (RR = 0.34, 95% CI = 0.1 to 0.9, for consumption of potassium iodide versus no consumption). Conclusion: Exposure to 131 I in childhood is associated with an increased risk of thyroid cancer. Both iodine defi ciency and iodine supplementation appear to modify this risk. These results have important public health implications: stable iodine supplementation in iodine-defi cient populations may substantially reduce the risk of thyroid cancer related to radioactive iodines in case of exposure to radioactive iodines in childhood that may occur after radiation accidents or during medical diagnostic and therapeutic procedures. [J Natl Cancer Inst 2005;97:724 – 32]

Risk of Thyroid Cancer After Exposure to 131I in Childhood

The Chernobyl reactor accident was followed by a sharp increase in the incidence of thyroid cancer among children and adolescents in Belarus (Belorussia) and Ukraine1,2. Exposure to iodine-131 (131I) was responsible for most of the doses that affected the thyroids of these children; however, among evacuees, up to 40% of each dose could derive from other incorporated radionuclides and external exposures3. From the data set compiled after this incident, we estimated the increased risk of developing thyroid cancer after exposure to radioactive iodine. The figure we obtained for most of the affected regions fell within the 95% confidence interval of a previous follow-up of thyroid cancer after external exposures.

Thyroid cancer risk to children calculated

The thyroid dose due to 131I releases during the Chernobyl accident was reconstructed for children and adolescents in two cities and 2122 settlements in Belarus, and in one city and 607 settlements in the Bryansk district of the Russian Federation. In this area, which covers the two high contamination spots in the two countries following the accident, data on thyroid cancer incidence during the period 1991–1995 were analysed in the light of possible increased thyroid surveillance. Two methods of risk analysis were applied: Poisson regression with results for the single settlements and Monte Carlo (MC) calculations for results in larger areas or sub-populations. Best estimates of both methods agreed well. Poisson regression estimates of 95% confidence intervals (CIs) were considerably smaller than the MC results, which allow for extra-Poisson uncertainties due to reconstructed doses and the background thyroid cancer incidence. The excess absolute risk per unit thyroid dose (EARPD) for the birth cohort 1971–1985 by the MC analysis was 2.1 (95% CI 1.0–4.5) cases per 104 person-year Gy. The point estimate is lower by a factor of two than that observed in a pooled study of thyroid cancer risk after external exposures. The excess relative risk per unit thyroid dose was 23 (95% CI 8.6–82) Gy−1. No significant differences between countries or cities and rural areas were found. In the lowest dose group of the settlements with an average thyroid dose of 0.05 Gy the risk was statistically significantly elevated. Dependencies of risks on age-at-exposure and on gender are consistent with findings after external exposures. © 1999 Cancer Research Campaign

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Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia.

The thyroid cancer incidence in the Ukraine among those born in the period 1968–1986 was analyzed with the aim to identify the enhancement due to the Chernobyl accident. Since any Ukrainian data referring to the time period before the accident are scarce and the variation of spontaneous incidences in other countries is immense, the Ukrainian incidences in the period 1986–1989 were used to estimate the baseline risk. Following 1990, the incidence in the southern part of the Ukraine increased by about 30%, independent of age. In the other parts the increase of the incidence depended on age at exposure. In the age group of 9-year-old children, the incidences in three regions defined as the `high-dose area', the northern, and the middle oblasts, increased by factors of 50, 20, and 6, respectively. These rates (1991–1995) are well above spontaneous rates in other countries. In the age group of 17-year-old juveniles, the incidence increased by a factor of 6 for the `high dose area' and in the three northern oblasts, whereas in the nine `middle' oblasts it was similar to the incidence of the `southern' Ukraine. These rates are within the range found in other countries.

W. F. Heidenreich

Papers

Thyroid cancer risk to children calculated

Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia.

Thyroid cancer incidence in the Ukraine after the Chernobyl accident: comparison with spontaneous incidences.