Annals of Occupational Hygiene Advance Access published online on February 17, 2006
Annals of Occupational Hygiene, doi:10.1093/annhyg/mel003
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1 Cancer Control Research, British Columbia Cancer Agency, 2-111, 675 West 10th, Vancouver, BC, Canada V5Z 1L3; School of Occupational and Environmental Hygiene, University of British Columbia, 372-2206 East Mall, Vancouver, BC, Canada V6T 1Z3
* To whom correspondence should be addressed. Objectives: Expert judgement of exposure levels is often only poorly or moderately correlated with directly measured levels. For a follow-up of a historical cohort study at a Söderberg aluminum smelter we updated an expert-based semiquantitative job exposure matrix of coal tar pitch volatiles (CTPV) to quantitative estimates of CTPV and benzo(a)pyrene (BaP). Methods: Mixed effects models to predict exposure for potroom operation and maintenance jobs were constructed from personal CTPV and BaP measurements. Mean exposures of jobs in non-potroom locations were directly calculated when measurements were available. Exposure estimates for jobs/time periods with no measurements were based on proportion of time spent in exposed areas compared to jobs where exposure was modeled or measured. For pre-1977, the original expert exposure assignments were calibrated using the updated 1977 estimates. Results: The rate of change in exposure levels varied by time period and was accounted for in mixed models with a linear spline time trend. Other variables significant in the models were job, potroom group and season as fixed effects, and worker as a random effect. The models for potroom operations explained 45 and 27% of the variability in the CTPV and BaP measurements, respectively. The models for maintenance jobs explained 40 and 19% of the variability in the CTPV and BaP measurements, respectively. For 1977-2000 model estimates, direct calculation of means and extrapolation from modeled/measured exposures accounted for 57, 6 and 37% of the exposed person-years, respectively. Conclusions: The above methodology maximized the use of exposure measurements and largely replaced the original expert-based estimates. Finer discrimination between exposure levels was possible with the updated exposure assessment. The new estimates are expected to reduce exposure misclassification and help better assess the exposure-response relationships.
Received September 8, 2005
Accepted January 4, 2006
Article
From Expert-based to Quantitative Retrospective Exposure Assessment at a Söderberg Aluminum Smelter
M. C. Friesen 1 *,
P. A. Demers 2,
J. J. Spinelli 3,
and
N. D. Le 3
2 School of Occupational and Environmental Hygiene, University of British Columbia, 372-2206 East Mall, Vancouver, BC, Canada V6T 1Z3
3 Cancer Control Research, British Columbia Cancer Agency, 2-111, 675 West 10th, Vancouver, BC, Canada V5Z 1L3
M. C. Friesen, E-mail: melissaf{at}interchange.ubc.ca
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