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Exposure estimates for workers in a facility expanding Libby vermiculite: updated values and comparison with original
Eric K Borton1, Grace K Lemasters, Timothy J Hilbert
1Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
Objective:
Low cumulative fiber exposure (CFE) has been associated with health effects in a cohort exposed to Libby vermiculite. This study refines the original 1980 exposure estimates and compares the CFE results.
Methods:
Cumulative fiber exposure estimates were developed using three times more industrial hygiene measurements and long-term workers' input. New adjustments included vermiculite ore source, seasonal overtime hours, time spent in various tasks, and recollection of historical dustiness.
Results:
The overall mean (95% confidence interval) CFE (n = 513) in 1980 (0.80 [0.69 to 0.93]) was statistically similar to the overall mean (95% confidence interval) CFE in 2010 (0.74 [0.61 to 0.90]). The mean CFE in the lowest exposure category (<2 fiber-years/cm) decreased from 0.36 to 0.22 fiber-years/cm (P < 0.05). The 2010 CFE estimate extended the upper bound of the range of previous estimates from 28.10 to 106.31 fiber-years/cm.
Conclusions:
The range of CFE values was expanded. These estimates may impact the understanding of Libby vermiculite health outcomes.
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