Change of Exposure Response over Time and Long-Term Risk of Silicosis among a Cohort of Chinese Pottery Workers

Yi Sun,Heijiao Wang,Yuewei Liu,Frank Bochmann,Lei Yang,Kurt Ulm,Peter Morfeld,Weihong Chen

doi:10.3390/ijerph8072923

Abstract

An analysis was conducted on a cohort of Chinese pottery workers to estimate the exposure-response relationship between respirable crystalline silica dust exposure and the incidence of radiographically diagnosed silicosis, and to estimate the long-term risk of developing silicosis until the age of 65. The cohort comprised 3,250 employees with a median follow-up duration of around 37 years. Incident cases of silicosis were identified via silicosis registries (Chinese X-ray stage I, similar to International Labor Organisation classification scheme profusion category 1/1). Individual exposure to respirable crystalline silica dust was estimated based on over 100,000 historical dust measurements. The association between dust exposure, incidence and long-time risk of silicosis was quantified by Poisson regression analysis adjusted for age and smoking. The risk of silicosis depended not only on the cumulative respirable crystalline silica dust exposures, but also on the time-dependent respirable crystalline silica dust exposure pattern (long-term average concentration, highest annual concentration ever experienced and time since first exposure). A long-term “excess” risk of silicosis of approximately 1.5/1,000 was estimated among workers with all annual respirable crystalline silica dust concentration estimates less than 0.1 mg/m3, using the German measurement strategy. This study indicates the importance of proper consideration of exposure information in risk quantification in epidemiological studies.

Highlights

Silicosis, one of the earliest recognized occupational diseases, is a pathological condition of the lungs due to inhalation of particulate matter containing crystalline silica [1]
Since crystalline silica was classified as a human carcinogen by IARC in 1997 [3], a series of quantitative risk assessments has been conducted for respirable silica dust exposure, especially for low exposure levels [4,5,6,7,8]
Previous analysis in the quantification of silicosis risk has often suffered from two types of limitation: limited historical exposure monitoring data; and poor comparability of exposure information reported in various studies or countries—differences in average crystalline silica dust exposure between industrialized countries of up to a factor of 12 were reported even in the same industrial sector and calendar periods [10]

Summary

Introduction

One of the earliest recognized occupational diseases, is a pathological condition of the lungs due to inhalation of particulate matter containing crystalline silica [1]. Silicosis may reflect a failure in adequate control of occupational dust exposure. Advances in occupational safety and health make this disorder highly preventable, silicosis remains the most prevalent occupational disease worldwide [2]. Since crystalline silica was classified as a human carcinogen by IARC in 1997 [3], a series of quantitative risk assessments has been conducted for respirable silica dust exposure, especially for low exposure levels [4,5,6,7,8]. The published exposure-response relationships and excess risk estimations have resulted in advanced risk communications, methodological limitations in published studies have stirred much debate within the scientific community. Besides the common problems in design, lack of adjustment of confounding [9], limited quality and poor comparability of exposure data between studies [10], inadequate consideration of exposure data or inappropriate biological assumptions of the exposure-response relationship in data analysis seem to be important limitations

Methods

Discussion

Conclusion