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TO DETERMINE THE CARCINOGENIC RISKS THROUGH INHALATION OF MAN-MADE MINERAL FIBERS IN COMPARISON WITH THE RISKS OF ASBESTOS EXPOSURE.
THE FIBERS ARE MILLED DOWN TO INHALABLE SIZES AND THEIR DISTRIBUTION EXAMINED BY SCANNING ELECTRON MICROSCOPY. FIBERS ARE DISPERSED BY A VIBRATING BED AEROSOL GENERATOR FOR ANIMAL EXPOSURE IN A SPECIALLY CONSTRUCTED EXPOSURE UNIT. GROUPS OF ABOUT 100 RATS ARE EXPOSED TO CROCIDOLITE, FIBROUS GLASS AND ROCKWOOL. THE CONTROL GROUP INHALES TITANIUM DIOXIDE. AFTER EXPOSURE, ANIMALS ARE KEPT TILL THEIR NATURAL DEATH. ORGANS ARE THEN EXAMINED HISTOPATHOLOGICALLY FOR TUMOURS. ADDITIONALLY, SMALLER GROUPS OF ANIMALS ARE EXPOSED TO THE FIBER AEROSOL AND SACRIFIED AT DIFFERENT TIMES AFTER THE TREATMENT FOR DETERMINATION OF THE NUMBER OF FIBERS IN LUNGS.