Silicosis in workers dealing with tonoko: case reports and analyses of tonoko

We found three cases of pneumoconiosis among those workers who had been dealing with tonoko (a mineral powder) for more than ten years at a shop making wooden furniture in Sendai, Japan. In the factory the workers were exposed to tonoko dust and had been inhaling it for a long time. Until now, this disease has not been found in employees of furniture factories; and, furthermore, tonoko has not been regarded as a harmful material. Tonoko is a very fine mineral powder used widely in Japan for filling the grains of surfaces of wooden products. The three workers had scanty clinical symptoms; however, their chest x-ray films revealed disseminated nodulations throughout both pulmonary fields. One of the workers suffered from the complication of active pulmonary tuberculosis. Some of the analyses revealed that tonoko contained about 50% quartz. Accordingly, the disease is strongly suspected to be a sort of silicosis caused by inhalation of tonoko dust.