A Novel Strategy for Retrospective Exposure Assessment in the Norwegian Silicon Carbide Industry

Abstract

The objective was to construct a retrospective job-exposure matrix (JEM) for the Norwegian silicon carbide industry. More than 3300 historical total dust measurements were available (1967–2005); however, there were few measurements of other agents. Total dust measurements were therefore used as the basis for the JEM, and a novel method was developed to estimate exposure to other agents. Multiple linear regression models were developed to describe historical exposure to total dust. Exposure estimates were extrapolated backward to periods without exposure data by adjustments for process and work-hour related changes. An exposure assessment study was performed where total dust was sampled in parallel with fibers or respirable dust. The respirable dust was analyzed for the content of quartz, cristobalite, and silicon carbide. Mixed-effect models were developed to estimate the exposure to these agents from total dust exposure, plant, and job group. Exposure to asbestos and polycyclic aromatic hydrocarbons was assigned qualitatively. Multiple linear regression models of total dust described historical exposure best in the furnace department (R² _adj = 0.49–0.74). Models in the other departments explained less variance (R² _adj = 0.12–0.32). Exposure determinants and total dust explained a substantial proportion of the between- (70–100%) and within-worker (8.0–54%) variance in the mixed-effect models. The relative bias between available historical measurements and the estimated exposure to dust components varied between –39% (fiber) and 40% (quartz). However, corrections were not considered necessary due to limitations in the historical data. The component-specific metrices were sufficiently different from each other (r_Pearson < 0.7), with the exception of total and respirable dust (r_Pearson = 0.84) and total dust and cristobalite (r_Pearson = 0.72), and will enable component-specific epidemiologic analyses in the future. Improved and less correlated estimates of exposure levels for the different components in the dust were obtained with the updated exposure assessment. Due to limitations in the measurement data, assumptions had to be made, especially in the period before 1967.

[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a file containing tables outlining multiple linear regression models for prediction of total dust exposure in the processing departments of Norwegian SiC producing plants, evaluation of the predictive abilities of the reduced total dust models, and mixed models for pedicting exposure to fibers and respirable quartz, cristobalite, non-fibrous silicon carbide and respirable dust from total dust exposure.]

Keywords:

• crystalline silica
• exposure modeling
• fiber
• job- exposure matrix
• retrospective exposure assessment
• silicon carbide production

ACKNOWLEDGMENTS

We greatly appreciate the cooperation of the Norwegian SiC production plants: Washington Mills AS, Saint-Gobain Ceramic Materials AS Lillesand and Arendal. Financial support was provided by the Ministry of Labor and Social Inclusion, the Research Council of Norway, the Confederation of Norwegian Business and Industry Work Environmental Fund, and the three Norwegian silicon carbide plants. We are grateful to Dr. Jay H. Lubin for providing us with the SAS macro for the imputation procedure, and Dr. Roel Vermeulen and Dr. Lützen Portengen for advice on using the SAS macro.