Comparison of Risk of Silicosis in Metal Mines and Pottery Factories: A 44-Year Cohort Study.

BACKGROUND

Little is known about the different risk of silicosis in metal mines and pottery factories. We aimed to compare the silicosis risks among silica-exposed workers in different industrial circumstances.

RESEARCH QUESTION

Are the silicosis risks among silica-exposed workers in industrial circumstances different?

STUDY DESIGN AND METHODS

We studied 39,808 workers followed up from January 1, 1960 to December 31, 2003 in China. Cumulative respirable silica dust exposure (CDE) was estimated by linking a job-exposure matrix to personal work history. Silicosis of stage I or higher was diagnosed by Chinese pneumoconiosis Roentgen diagnostic criteria.

RESULTS

A total of 9,377 silicosis patients were diagnosed during 1,153,580.9 person-years' follow-up in the cohort. Hazard ratios of silicosis for each 1 mg/m-year increase in CDE were 1.08 (1.07-1.08) for tungsten mines, 1.41 (1.33-1.48) for iron and copper mines, 1.14 (1.11-1.17) for tin mines, and 1.03 (1.02-1.04) for pottery factories, respectively. When exposed to 0.05 mg/m of respirable silica dust for 45 years, the cumulative risks in metal mines (2.3%, 9.9%, 1.5% for tungsten mines, iron and copper mines, and tin mines, respectively) were still higher than those in pottery factories (0.6%). The joint effect of silica and smoking on silicosis was more than multiplicative.

INTERPRETATION

The risk of silicosis in metal miners is higher than that in pottery workers when exposed to the same level of silica dust. The silica dust exposed years should be under 10 years for metal miners and 40 years for pottery workers at 0.05 mg/m to keep lifetime risk within 0.1%. Current exposure limits should take into account differences in various industrial circumstances. Smoking cessation could help reduce silicosis risk for silica-exposed workers.