Ann. occup. Hyg., Vol. 47, No. 6, pp. 477-484, 2003
© 2003 British Occupational Hygiene Society
Published by Oxford University Press
Validation of a Semi-quantitative Job Exposure Matrix at a Söderberg Aluminum Smelter
1 Cancer Control Research, British Columbia Cancer Agency, 201–601 West Broadway, Vancouver, BC V5Z 4C2, Canada; 2 School of Occupational and Environmental Hygiene, University of British Columbia, Room 372, 2206 East Mall, Vancouver, BC V6T 1Z3, Canada
Received 16 October 2002; in final form 17 March 2003
Objectives: We tested the validity of a job exposure matrix (JEM) for coal tar pitch volatiles (CTPV) at a Söderberg aluminum smelter. The JEM had been developed by a committee of company hygienists and union representatives for an earlier study of cancer incidence and mortality. Our aim was to test the validity and reliability of the expert-based assignments. Methods: Personal CTPV exposure measurements (n = 1879) overlapped 11 yr of the JEM. The arithmetic mean was calculated for 35 job/time period combinations (35% of the exposed work history), categorized using the original exposure intervals, and compared with the expert-based assignments. Results: The expert-based and the measurement-based exposure assignments were only moderately correlated (Spearman’s 
= 0.42; weighted 
= 0.39, CI 0.10–0.69). Only 40% of the expert-based medium category assignments were correctly assigned, with better agreement in the low (84%) and high (100%) categories. Pot operation jobs exhibited better agreement ( = 0.60) than the maintenance and pot shell repair jobs ( = 0.25). The mid-point value of the medium category was overestimated by 0.3 mg/m3. Conclusions: The expert-based exposure assignments may be improved by better characterizing the transitions between exposure categories, by accounting for exposure differences between pot lines and by re-examining the category mid-point values used in calculating the cumulative exposure. Lack of historical exposure measurements often requires reliance on expert knowledge to assess exposure levels. Validating the experts’ estimates against available exposure measurements may help to identify weaknesses in the exposure assessment where improvements may be possible, as was shown here.
Keywords: coal tar pitch volatiles; cohort studies; occupational exposure; polycyclic aromatic hydrocarbons; reproducibility of results; retrospective studies
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