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

High doses of ionizing radiation clearly produce deleterious consequences in humans, including, but not exclusively, cancer induction. At very low radiation doses the situation is much less clear, but the risks of low-dose radiation are of societal importance in relation to issues as varied as screening tests for cancer, the future of nuclear power, occupational radiation exposure, frequent-flyer risks, manned space exploration, and radiological terrorism. We review the difficulties involved in quantifying the risks of low-dose radiation and address two specific questions. First, what is the lowest dose of x- or γ-radiation for which good evidence exists of increased cancer risks in humans? The epidemiological data suggest that it is ≈10–50 mSv for an acute exposure and ≈50–100 mSv for a protracted exposure. Second, what is the most appropriate way to extrapolate such cancer risk estimates to still lower doses? Given that it is supported by experimentally grounded, quantifiable, biophysical arguments, a linear extrapolation of cancer risks from intermediate to very low doses currently appears to be the most appropriate methodology. This linearity assumption is not necessarily the most conservative approach, and it is likely that it will result in an underestimate of some radiation-induced cancer risks and an overestimate of others.

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Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know

Oxidative stress-the production and accumulation of reduced oxygen intermediates such as superoxide radicals, singlet oxygen, hydrogen peroxide, and hydroxyl radicals-can damage lipids, proteins, and DNA. Many disease processes of clinical interest and the aging process involve oxidative stress in their underlying etiology. The production of reactive oxygen species is also prevalent in the world's oceans, and oxidative stress is an important component of the stress response in marine organisms exposed to a variety of insults as a result of changes in environmental conditions such as thermal stress, exposure to ultraviolet radiation, or exposure to pollution. As in the clinical setting, reactive oxygen species are also important signal transduction molecules and mediators of damage in cellular processes, such as apoptosis and cell necrosis, for marine organisms. This review brings together the voluminous literature on the biochemistry and physiology of oxidative stress from the clinical and plant physiology disciplines with the fast-increasing interest in oxidative stress in marine environments.

Oxidative stress in marine environments: biochemistry and physiological ecology.

Reports that promote persulfate-based advanced oxidation process (AOP) as a viable alternative to hydrogen peroxide-based processes have been rapidly accumulating in recent water treatment literature. Various strategies to activate peroxide bonds in persulfate precursors have been proposed and the capacity to degrade a wide range of organic pollutants has been demonstrated. Compared to traditional AOPs in which hydroxyl radical serves as the main oxidant, persulfate-based AOPs have been claimed to involve different in situ generated oxidants such as sulfate radical and singlet oxygen as well as nonradical oxidation pathways. However, there exist controversial observations and interpretations around some of these claims, challenging robust scientific progress of this technology toward practical use. This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfate and the formation pathways of oxidizing species. Properties of the main oxidizing species are scrutinized and the role of singlet oxygen is debated. In addition, the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry are discussed. The opportunity for niche applications is also presented, emphasizing the need for parallel efforts to remove currently prevalent knowledge roadblocks.

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Persulfate-Based Advanced Oxidation: Critical Assessment of Opportunities and Roadblocks.

How Easily Oxidizable Is DNA? One-Electron Reduction Potentials of Adenosine and Guanosine Radicals in Aqueous Solution

Nikjoo, H., O'Neill, P., Wilson, W. E. and Goodhead, D. T. Computational Approach for Determining the Spectrum of DNA Damage Induced by Ionizing Radiation. Radiat. Res. 156, 577–583 (2001). To study the characteristics of molecular damage induced by ionizing radiation at the DNA level, Monte Carlo track simulation of energetic electrons and ions in liquid water, a canonical model of B-DNA, and a comprehensive classification of DNA damage in terms of the origin and complexity of damage were used to calculate the frequencies of simple and complex strand breaks. A threshold energy of 17.5 eV was used to model the damage by direct energy deposition, and a probability of 0.13 was applied to model the induction of a single-strand break produced in DNA by OH radical reactions. For preliminary estimates, base damage was assumed to be induced by the same direct energy threshold deposition or by the reaction of an OH radical with the base, with a probability of 0.8. Computational data are given on the comp...

Computational Approach for Determining the Spectrum of DNA Damage Induced by Ionizing Radiation

Modelling and calculations are presented as a first step towards mechanistic interpretation and prediction of radiation effects based on the spectrum of initial DNA damage produced by low energy electrons (100eV-4.5keV) that can be compared with experimental information. Relative yields of single and clustered strand breaks are presented in terms of complexity and source of damage, either by direct energy deposition or by reaction of OH radicals, and dependence on the activation probability of OH radicals and the amount of energy required to give a single strand break (ssb). Data show that the majority of interactions in DNA do not lead to damage in the form of strand breaks and when they do occur, they are most frequently simple ssb. However, for double-strand breaks (dsb), a high proportion (30%) are of more complex forms, even without considering additional complexity from base damage. The greater contribution is from direct interactions in the DNA but reactions of OH radicals add substantially to this...

Computational modelling of low-energy electron-induced DNA damage by early physical and chemical events.

Formation of radical cations of methoxylated benzenes by reaction with hydroxyl radicals, thallium(2+), silver(2+), and peroxysulfate (SO4.-) in aqueous solution. Optical and conductometric pulse radiolysis and in situ radiolysis electron spin resonance study

Purpose: To investigate quantitatively the induction and rejoining of DNA double strand breaks (DSB) in V79-4 and xrs-5 Chinese hamster cells and HF19 human fibroblast cells, using the phosphorylat...

Induction and quantification of γ-H2AX foci following low and high LET-irradiation

Publisher Summary This chapter discusses the primary free radical processes in DNA following the initial spatial distribution of energy deposition. In an attempt to characterize the DNA radicals formed within microseconds of irradiation, the transient diffuse reflectance spectra of pulse-irradiated dry samples of poly (A), poly (G), poly (U), and poly(C) were determined and compared to that from dry DNA. Electron transfer may occur from the purine radical to yield the pyrimidine electron adduct using a series of mixed dinucleoside phosphates. In the case of adenine, electron donation from the adduct is in competition with its protonation. End group analysis of the stable products upon irradiation of DNA has identified important differences between single-stranded binding (SSB) produced by OH radicals and those produced on irradiation of frozen aqueous solutions where OH radicals have limited diffusion. Whereas SSB formed under these conditions yield 5'-phosphate end groups, the ·OH radical produces both 3'-phosphate and 3'-phosphoglycolate end groups. 32 P-postlabeling has also been utilized to identify ·OH-induced formation of thymine glycols and phosphoglycolate end groups. The extension of this technique to DNA irradiated under different states of hydration may provide more valuable insights into the action of radiation pertinent to the cellular environment.

Peter O'Neill

Papers

Computational Approach for Determining the Spectrum of DNA Damage Induced by Ionizing Radiation

Computational modelling of low-energy electron-induced DNA damage by early physical and chemical events.

Formation of radical cations of methoxylated benzenes by reaction with hydroxyl radicals, thallium(2+), silver(2+), and peroxysulfate (SO4.-) in aqueous solution. Optical and conductometric pulse radiolysis and in situ radiolysis electron spin resonance study

Induction and quantification of γ-H2AX foci following low and high LET-irradiation

Primary Free Radical Processes in DNA