Quantitative Crystalline Silica Exposure Assessment for a Historical Cohort Epidemiologic Study in the German Porcelain Industry

Abstract

A time-dependent quantitative exposure assessment of silica exposure among nearly 18,000 German porcelain workers was conducted. Results will be used to evaluate exposure-response disease risks. Over 8000 historical industrial hygiene (IH) measurements with original sampling and analysis protocols from 1954–2006 were obtained from the German Berufs- genossenschaft der keramischen-und Glas-Industrie (BGGK) and used to construct a job exposure matrix (JEM). Early measurements from different devices were converted to modern gravimetric equivalent values. Conversion factors were derived from parallel historical measurements and new side-by-side measurements using historical and modern devices in laboratory dust tunnels and active workplace locations. Exposure values were summarized and smoothed using LOESS regression; estimates for early years were derived using backward extrapolation techniques. Employee work histories were merged with JEM values to determine cumulative crystalline silica exposures for cohort members. Average silica concentrations were derived for six primary similar exposure groups (SEGs) for 1938–2006. Over 40% of the cohort accumulated <0.5 mg; just over one-third accumulated >1 mg/m3-years. Nearly 5000 workers had cumulative crystalline silica estimates >1.5 mg/m3-years. Similar numbers of men and women fell into each cumulative exposure category, except for 1113 women and 1567 men in the highest category. Over half of those hired before 1960 accumulated >3 mg/m3-years crystalline silica compared with 4.9% of those hired after 1960. Among those ever working in the materials preparation area, half accumulated >3 mg/m3-year compared with 12% of those never working in this area. Quantitative respirable silica exposures were estimated for each member of this cohort, including employment periods for which sampling used now obsolete technologies. Although individual cumulative exposure estimates ranged from background to about 40 mg/m3-years, many of these estimates reflect long-term exposures near modern exposure limit values, allowing direct evaluation of lung cancer and silicosis risks near these limits without extrapolation. This quantitative exposure assessment is the largest to date in the porcelain industry.