To the question of maximal permissible load with chemical substances in man.

The authors introduce an over-all evaluation of a maximum admissible drug load in man, as related to professional exposure, environmental atmosphere, water, soil, and foodstuffs. To minimize the occurrence of lesions, it is necessary to disclose and classify the environmental factors responsible for homeostasis of the human organism. Moreover, it is desirable to establish the limits of biologically adverse changes of the medium. A real adaptation is possible provided the above changes are sufficiently slow and enable development of optimum mechanisms of reactions within the biological homeostasis. The establishment of an effective system for optimalization of man's environment necessitates further advancement and improvement of methods and their more adequate selection. This adequacy should respond to the real conditions of evaluation of relationships of man and populations with dynamically changing environment. The understanding of general regularities and mechanisms of this complex action will be indispensable. The to-date experience implies that the criteria for determination of the maximum permissible load of environment and man with chemical compounds are quantitative relationships between intensity, frequency and duration of exposure to chemicals in the atmosphere, and the magnitude of undesirable changes in man and his environment. The classification of acceptable or permissible limits of concentration (or other index of exposure) of chemical substances in the atmosphere pursues the protection of the population from undesirable effects under variable conditions of exposure (chemical compounds in working places, atmosphere, alien foreign substances in food, water or soil). The number of potentially toxic substances to be evaluated both hygienically and toxicologically, amounts to about 25 000. Newly introduced chemical compounds annually make about 1000-5000, of which approximately 10% need a thorough examination. The limits can be divided into several groups: Maximum permissible concentrations of chemical compounds (MAC) in working and external atmosphere, water, and partially in soil and food. For these a denomination "derived working limits". Limits of chemical compounds based on their intake by the human organism are sometimes called "primary protection standard". These may correlate with the acceptable daily intake of foreign substances (additives and contaminating substances). The longest tradition enjoys the classification of food additives, which has been supervised since 1956 by the Joint Committee of FAO experts and WHO experts for pesticide residues (1).(ABSTRACT TRUNCATED AT 400 WORDS)