65 J. Descotes Centre Anti-Poison de Lyon, et Laboratoire de Pharmacologie et Toxicologie Médicale, INSERM U80, Faculté de Médecine A.-Carrel, Lyon, France Editorial Risk Analysis and Toxicology In recent years, the concept of risk assessment has been used increasingly by toxicologists and health profession- als. However, the definitions of terms concerned with such risk assessment are a source of confusion, are not widely accepted, and so hamper the understanding of the subject, presumably because it is still a recent and multi- disciplinary field [ 1 ]. Hazard is the ability to cause an adverse effect. As far as chemical substances are concerned, hazard includes flammability, explosivity, radioactivity, causticity and toxicity. Risk and hazard are definitely not synonyms. Risk is the probability that some harmful event will occur. Uncertainty is therefore a major component of risk. Risk assessment is the process which describes and quantifies the risk associated with exposure to a hazardous (toxic) substance. It is based on toxicological data obtained in animals, and possibly in humans, the evidence of a dose- response relationship, and finally on data regarding the actual or estimated human exposure [2]. The words risk characterisation, evaluation or estimation are often used synonymously. They represent the process which at- tempts to produce an estimate of the likelihood of observ- ing the toxic effect in the population under study. Finally, risk analysis is a global process which includes hazard identification, risk assessment, risk characterization and the perception of risk. Risk analysis, particularly as far as toxic substances are concerned, covers five aspects at least. The first aspect is hazard identification. Animal and, to a lesser extent, in vitro toxicity studies, are conducted to establish whether a given substance can cause toxic effects in humans. It should be emphasised that hazard identification is ge- nuinely a qualitative process and the quality of the infor- mation provided depends on the choice of appropriate control groups, the use of sufficient numbers of animals, the selection of rigorous experimental protocols, the se- verity of the effects described and the relevance to man of the toxic mechanism involved. The result is a scientific judgement that the substance can cause toxic effects in humans at some exposure levels [3]. The second component of risk analysis is the origin or source of risk. This will include, for a substance, all rele- vant information on the composition of formulations con- taining it on the market (hence the need, seldom met, for a detailed description of all components and their respec- tive concentration in the formulation), the name of all commercial products which include the substance, and the amount manufactured or distributed in a given period of time. The origin of risk should be kept under close scru- tiny, for example, all relevant data about possible changes in use must be kept, such as, the amount manufactured, and changes in the recommended or actual modes of use. Measurements of a substance in the air, water, food chain, or in biological fluids (blood or urine) are useful for quan- tifying the origin of risk. They are also useful for checking the effectiveness of preventive measures intended to de- crease or control the risk. However, their usefulness is limited by several factors: the information obtained is always retrospective, the relevance of selected endpoints is often uncertain; and the cost of field studies is usually very high. Data are sometimes collected in very particular circumstances (e.g. real or simulated chemical catas- trophes), but the relevance of the information gained in such extreme conditions is dubious. Human exposure is the third component of risk analy- sis. Information should be obtained, where possible, on the duration, magnitude, and route(s) of exposure, and on the number and characteristics (e.g. gender, age, occupa-