A 40-year follow-up of whetstone cutters on silicosis.

The present study, consisted of two separate surveys, was initiated to clarify the development of clinical pictures of silicosis after termination of dust exposure. The first survey was a 40-year follow-up of radiographic pictures of the chest among 200 male whetstone cutters (Group I workers). The second survey was conducted in 75 male recipients (Group II workers) of disability compensation for silicosis due to whetstone dust exposure. The study on Group I workers made it clear that the proportion of those free of radiographic findings in the chest pictures decreased during a 40-year follow-up period from 84% in the 1st health examination in 1952-6 to 36% in the 3rd examination in 1995. The rate of progression of the disease from Category 1 to 3 (after ILO-guided classification) to higher categories in a 15-year period was as high as >50%. Longer service duration and higher category of chest radiography at the previous health examination were the influential factors in determining the rapid progression of silicosis. The latter observation was confirmed also through a similar analysis on Group II workers. Whetstone preparations contained SiO2 by about 50%. No industrial hygiene data were available for both groups of stone cutters, but the exposure of Group I workers was estimated to be about 1 mg/m3, or well in excess of the current occupational exposure limit.