Institutional members access full text with Ovid®

Share this article on:

Threshold Value Estimation for Respirable Quartz Dust Exposure and Silicosis Incidence Among Workers in the German Porcelain Industry

Morfeld, Peter PD; Mundt, Kenneth A. Dr med; Taeger, Dirk Dr med; Guldner, Karlheinz Dr med; Steinig, Othmar Dipl-Ing; Miller, Brian G. Dr med

Journal of Occupational and Environmental Medicine: September 2013 - Volume 55 - Issue 9 - p 1027–1034
doi: 10.1097/JOM.0b013e318297327a
Original Articles

Objectives: To estimate a threshold value for the respirable quartz dust concentration and silicosis incidence (1/1, ILO 1980/2000) in the German porcelain worker cohort.

Methods: Forty incident cases occurred among 17,144 workers. Estimation of the relationship to cumulative respirable quartz dust exposures by using Cox regression with restricted cubic splines (7 knots or less) and fractional polynomials (degrees 5 or less). Threshold estimates were obtained by subtracting candidate values from the time-dependent concentration data (setting the result to zero if negative) and recalculating cumulative exposure.

Results: Best threshold estimate was 0.25 mg/m3 (95% confidence interval: 0.15 to 0.30 mg/m3).

Conclusions: A concentration threshold for silicosis risk is plausible. A threshold Cox model fitted the data significantly better than a nonthreshold model, summarized the cohort information without a loss in extracted information and more simply than restricted cubic splines and fractional polynomials.

From the Institute for Occupational Epidemiology and Risk Assessment of Evonik Industries AG (Dr Morfeld), Essen, Germany; Institute and Policlinic for Occupational Medicine, Environmental Medicine and Prevention Research (Dr Morfeld), University of Cologne, Germany; ENVIRON International Corporation (Dr Mundt), Amherst, Mass; Institute for Prevention and Occupational Medicine of the German Social Accident Insurance (Dr Taeger), Institute of the Ruhr-Universität Bochum (IPA), Germany; Verwaltungs-Berufsgenossenschaft (Dr Guldner and Mr Steinig), Würzburg, Germany; Institute of Occupational Medicine (Dr Miller), Edinburgh, United Kingdom.

Address correspondence to: PD Dr Peter Morfeld, Institute for Occupational Epidemiology and Risk Assessment of Evonik Industries, AG Rellinghauser Straße 1-11, 45128 Essen, Germany (

The study was supported by EUROSIL, representing the European industrial silica producers (, the National Industrial Sand Association (North America) (, and the Verwaltungs-Berufsgenossenschaft (

EUROSIL and the National Industrial Sand Association did not participate in any scientific aspects of this investigation.

The authors declare no conflicts of interest.

Copyright © 2013 by the American College of Occupational and Environmental Medicine