Collection Occupational hygiene, Issue 29, 1993 year
General requirements for inhalation exposure to aerosols on rats in order to simulate intoxication
M. A. Klisenko, L. G. Aleksandrova
doi
Institute of Occupational Medicine, Kiev
Research Institute of Occupational Hygiene and Occupational Diseases, Yekaterinburg
In recent years, there has been a significant increase in the nomenclature of new industrial chemicals, natural raw materials, aerosols of which are subject to hygienic assessment. The main data for judging the value of maximum permissible concentrations (MPC) of aerosols is provided by the study of their fibrogenic and toxic effects during prolonged inhalation into the body. The setting up of such experiments on animals requires not only taking into account a number of issues related to the nature and physicochemical properties of aerosols, but also the appropriate equipment - inhalation chambers, aerosol generators, dust detectors, aerosol concentration control devices, etc.
Inhalation exposure to aerosols on laboratory animals in order to simulate intoxication, pneumoconiosis and other reactions to such exposure differs from their inhalation inoculation with gases and vapors due to specific features associated with the properties of aerodispersed systems and some special research tasks. In turn, both the requirements for exposure conditions and design solutions when creating installations for said exposure can vary significantly depending on the properties of the aerosols under study, for example, from the study of disintegration or condensation aerosol in a solid or liquid dispersed phase, a substance that has or not possessing pronounced resorptive toxicity, etc. The differences are also due to the specific objectives of the experiment, in particular, the question of the action of monodisperse aerosols with given particle sizes or the simulation of processes caused by an aerosol with a dispersed composition typical for a particular production; on the construction of dependencies of the type "dose - effect", "concentration - time - effect" or about experiments of a comparatively pathological plan; on tasks requiring short-term or chronic exposure, etc. The variety of requirements associated with this applies to both the aerosol generator and the exposure chamber.
In the practice of experimental research, two main types of chambers are used: with intra- and in-chamber placement of animals. Both types have both disadvantages and advantages, which manifest themselves differently depending on the properties of the aerosol and the objectives of the experiment. Many authors attribute the inevitability of immobilization stress, limited exposure time, the known limited number of animals exposed to simultaneous exposure to the disadvantages of installations with per chamber placement of animals; to the merits - the possibility of creating the most optimal conditions for uniform exposure to all animals of the experimental group (especially when they are placed on one level around the perimeter of the cylindrical chamber), as well as the absence of significant aerosol contamination of the animal's fur and skin.
With internal chamber placement of animals, the listed disadvantages are absent, besides, installations of this type are structurally simpler. However, conditions are created in them for a significantly greater dispersion of the individual magnitude of the dust load, as well as for the deposition of aerosol particles on the surface of the body with subsequent licking, and for some substances, also by absorption through the skin. The first drawback can be reduced by limiting the crowding of animals, and in a chronic experiment - also by systematic rearrangement of their internal chamber. They try to reduce the second disadvantage by placing animals in a chamber in the so-called. pencil cases ("houses"), however, it should be noted that this measure is not effective enough and in some cases the oral intake of the toxic substance licked from the wool and skin turns out to be comparable or even more significant than the inhalation itself. This artifact can lead to serious errors when using the results of a toxicology experiment to regulate MPCs or an estimated safe exposure level (OSEL).
The creation of a universal installation that would make it possible to solve any experimental problem associated with exposure of animals to various aerosols, apparently, can be of interest only for an extremely limited number of scientific institutions that are really faced with such a wide range of problems. At the same time, this research will require a rather complex design development, multilateral testing of prototypes and significant costs.