[Biological markers of exposure to toxic agents].

Exposure to chemical agents may be assessed either qualitatively or semi-quantitatively with the help of a questionnaire (type of exposure and duration) or quantitatively either by the measurement of the concentration of the xenobiotics in the environment (ambient monitoring) or by the measurement of biological parameters related to the internal doses (biological monitoring of exposure). In industry, ambient monitoring usually implies the measurement of chemicals in air with static or personal samplers. The internal doses may be assessed either by measuring the chemical or its biotransformation products in biological media or by measuring some biological effects caused by the chemical. Depending on the selected biological parameter and the time of sampling, the result may reflect the amount of chemical recently absorbed, the amount stored in the organism (body burden) or the amount of active metabolites bound to the site of action. The biological parameter of exposure is more directly related to the adverse health effects that one attempts to prevent than any environmental measurement. Biological monitoring may take into consideration absorption by all the routes and from all sources (occupational and environmental), interindividual differences in toxicokinetic and in hygiene habits. The application of a biological test requires the critical evaluation of several factors, namely the sensitivity and the specificity of the test, the precision and the accuracy of the analytical method and eventually ethical aspects.