Some Methods Used in Establishing the Maximum Allowable Concentrations

The continuous increase in the number of new chemical substances introduced into industry, or arising in the course of production, forces us to search for faster methods of establishing the maximum allowable concentrations (M.A.C.'s). It is obvious that the M.A.C. can only be one that does not have any harmful effects on the human organism in the course of full-time work of long duration. It is, of course, impossible to design an experiment which could give an immediate answer to the problem. Only later can actual experience provide such a test, but, if the accepted M.A.C. has been set too high, the price paid for such an experiment is also high and might involve the loss of human life. The results of regular medical examination of the workers, especially those working in an atmosphere filled with harmful substances, and other clinical and statistical data, can serve as material only for the correction of M.A.C.'s already determined. When a new substance is put into production, such information usually is not available. In these cases, only research can help. Such experiments are of great importance when determining the M.A.C.'s for irritant gases and fumes. We are forced to use experiments with animals in order to determine whether concentrations which have no harmful effect on humans exposed for short periods do have harmful effects in the case of long-term exposure. The need for the rapid determination of the M.A.C.'s of substances newly introduced into industry does not allow these experiments to be carried out over the whole life-span. That is why, in such cases, it is not possible to reproduce the conditions which would apply to the human organism, even with respect to the overall length of exposure. Therefore it is all the more important to use highly sensitive methods, which make it possible to register even minor changes in the organism of the animal. I will not discuss the various methods covered ,by the highly interesting and informative articles of Barnes and Denz, nor many of the methods used in the Soviet Union. I will discuss only various methods, worked out on the basis of a common principle. In order to make this principle more comprehensible, let me remind you of the differences in the aims of the experiments carried out by a pharmacologist, and by a specialist in industrial toxicology. The pharmacologist is primarily interested in finding new drugs, and is, therefore, interested in the