A BASIC TOXICITY CLASSIFICATION of RADIONUCLIDES the Following States Are Members of the International Atomic Energy Agency

TECHNICAL REPORTS SERIES No. 15 I \ Basic • Toxicity Classification () f Radionuclides • REPORT OF JOINT STUDY OF A GROUP OF CONSULTANTS TO THE INTERNATIONAL ATOMIC ENERGY AGENCY INTERNATIONAL ATOMIC ENERGY AGENCY - VIENNA 1963 A BASIC TOXICITY CLASSIFICATION OF RADIONUCLIDES The following States are Members of the International Atomic Energy Agency: AFGHANISTAN ITALY ALBANIA JAPAN ARGENTINA REPUBLIC OF KOREA AUSTRALIA LEBANON AUSTRIA LIBERIA BELGIUM LUXEMBOURG BOLIVIA MALI BRAZIL MEXICO BULGARIA MONACO BURMA MOROCCO BYELORUSSIAN SOVIET SOCIALIST REPUBLIC NETHERLANDS CAMBODIA NEW ZEALAND CANADA NICARAGUA CEYLON NORWAY CHILE PAKISTAN CHINA PARAGUAY COLOMBIA PERU CONGO (LÊOPOLDVILLE). PHILIPPINES CUBA POLAND CZECHOSLOVAK SOCIALIST REPUBLIC PORTUGAL DENMARK ROMANIA DOMINICAN REPUBLIC SAUDI ARABIA ECUADOR SENEGAL EL SALVADOR SOUTH AFRICA ETHIOPIA SPAIN FINLAND SUDAN FRANCE SWEDEN FEDERAL REPUBLIC OF GERMANY SWITZERLAND GHANA THAILAND GREECE TUNISIA GUATEMALA TURKEY HAITI UKRAINIAN SOVIET SOCIALIST REPUBLIC HOLY SEE UNION OF SOVIET SOCIALIST REPUBLICS HONDURAS UNITED ARAB REPUBLIC HUNGARY UNITED KINGDOM OF GREAT BRITAIN AND ICELAND NORTHERN IRELAND INDIA UNITED STATES OF AMERICA INDONESIA URUGUAY IRAN VENEZUELA IRAQ VIET-NAM ISRAEL YUGOSLAVIA The Agency's Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of the Agency are situated in Vienna. Its principal objective is "to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world". © IAEA, 1963 Permission to reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Kárntner Ring 11, Vienna I, Austria. Printed by the IAEA in Austria April 1963 TECHNICAL REPORTS SERIES No. 15 A BASIC TOXICITY CLASSIFICATION OF RADIONUCLIDES REPORT OF JOINT STUDY OF A GROUP OF CONSULTANTS TO THE INTERNATIONAL ATOMIC ENERGY AGENCY INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA 1963 A BASIC TOXICITY CLASSIFICATION OF RADIONUCLIDES IAEA, VIENNA, 1963 STI/DOC/10/15 FOREWORD To facilitate the application of radiation protection regulations and recommendations, it may be necessary in some cases to classify radionuclides into groups according to their radiotoxicity. The Agency convened a group of consultants to consider this problem and make a study of the radiotoxicity grading and grouping based on the data provided by the International Commission on Radio- logical Protection (ICRP), in particular the Report of Committee II on Permissible Dose for Internal Radiation. The result of such work is the present report which presents a basic toxicity classification of radionuclides. This classification, however, may need some adjustments when applied to operations which depart from the conditions upon which the classification was based. CONTENTS 1. Introduction 9 2. Definition of Toxicity 10 3. Why is a Toxicity Grading and Classification Possible for Radionuclides! 11 4. Basis of the Toxicity Grading 11 5. Basic Toxicity Grading of Radionuclides 13 6. Basic Toxicity Classification taking into Account Specific Activity 14 Annexe I Mathematical Basis of Toxicity Grading for Continuous or Single Intake of Radionuclides 16 1. INTRODUCTION In the course of its work in the field of health and safety the International Atomic Energy Agency has often met the practical re- quirement for grading radionuclides in order of their relative radio- toxicities. This need was particularly evident when the Agency's Basic Safety Standards for the protection of health against ionizing radiation [3] were in preparation, when it was necessary to exempt quantities of radionuclides from inclusion in the norms. A basic toxicity grading might be of help to laboratories in meeting some of their requirements in problems related to waste management as well as for the design of experimental facilities. It should also serve as a basis for the development of safety criteria for laboratory equip- ment and procedures for handling and transporting various quantities and kinds of radionuclides. The purpose of the present Report is to make a toxicity grading of the radionuclides according to the risk of biological injury which they may cause when they have become incorporated in the human body. No account has been taken of the biological effects of radiation penetrating the body when the radionuclide is external to it. Inform- ation on the metabolism and subsequent biological risk from radionuclides taken into the body has been freely taken from the Report of Committee II of the International Commission on Radiological Pro- tection (ICRP) [1] . This information has been used in the present Report to show that a factor of about 108 in relative toxicity exists between radionuclides with the highest and lowest toxicities. Such a wide range of toxicities makes it necessary, especially in regu- latory procedures, to group the radionuclides within the toxicity grading so that recommendations or regulations may be made applicable to each of a small number of groups rather than to a large number of different toxicities of the individual radionuclides. In the present classification only three main groups have been distinguished. Radionuclides of high toxicity and those of low toxicity have been separated from a larger group of medium-toxicity nuclides. However, it is recognized that, for some purposes, the group of medium- toxicity nuclides may cover too wide a range of toxicity and there- fore a further division is suggested which splits the group into two sub-groups. The exact arrangement of the toxicity grading and the division into groups may depend on the particular application for which it is required. The IAEA has already developed a toxicity classification of radionuclides for transport purposes [4]. While that classification may require some reconsideration with a view to modification in the 9 light of the present Report, it is recognized that the basic classification as derived here would not be directly applicable to transport without adjustment to take due account of factors and circumstances which are peculiar to such application. One special factor which is important in all applications of toxicity grading and classification is specific activity. Hence in this Re- port a method is given for taking specific activity into account in the classification. 2. DEFINITION OF TOXICITY No agreed definition is available regarding what is meant by the toxicity of a radionuclide. However it may be useful to examine an accepted definition of chemical toxicity to see how it can guide the development of a similar definition for radionuclides. GOLDWATER [2] defines toxicity and the closely related concept of toxicity hazard as follows: "Toxicity is the ability of a chemical molecule or compound to produce injury once it reaches a susceptible site in or on the body. Toxicity hazard is the probability that injury may be caused by the manner in which the substance is used. " Similarly, we may adopt the following definition for the toxicity of a radionuclide: "The toxicity of a radionuclide is the ability of the nuclide to produce injury, by virtue of its emitted radiations, when incorporated in a body. " There are two important points of difference in the effects of a chemical toxin and a radionuclide which require some comment. Firstly, most attention is focused on the acute effects of chemical toxins, whereas the effects of all but the largest intake of radionuclides do not usually become apparent for several years, There- fore the degree of injury and the time of its manifestation are in general very different. Secondly, the susceptible site in the chemical definition has no exact counterpart in radionuclide definition but, in general, the site of greatest biological injury is in the body organ which accumulates the greatest concentration of the radionuclide. The body organ in which a radionuclide is most concentrated and the associated relative biological efficiency (RBE) dose is highest is, in general, called 'the critical organ' by the ICRP [1] . Factors other than the RBE dose were considered by the ICRP [1] in choosing the critical organ for a particular radionuclide, such as the essentiality of the organ and its radiosensitivity, but usually the RBE dose was the overriding consideration. A definition of toxicity hazard for a radionuclide may be obtained directly from that given by Goldwater for a chemical substance as follows: 10 "A toxicity hazard is the probability that injury may be caused by the manner in which the radionuclide is used. " If these proposed definitions of toxicity and toxicity hazard are accepted, then it becomes clear that the basic grading and classification of the radionuclides may be made purely on their toxicity, and any modification required due to the particular use of the radionuclide which might affect the probability of intake and subsequent injury as, for example, in the case of transport, changes the classification to one of toxicity hazard. Hence the present Report, in the terms of the above definitions, is concerned with a toxicity grading and classification and, in general, is not concerned with toxicity hazard. 3. WHY IS A TOXICITY GRADING AND CLASSIFICATION POSSIBLE FOR RADIONUCLIDES? It is almost impossible to grade non-radioactive nuclides in order of their toxicity because there is no way of quantitatively com- paring the various

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