Quoted from http://highwire.stanford.edu/cgi/medline/pmid;22544163
Mesothelioma Associated With Commercial Use of Vermiculite Containing Libby Amphibole.
KK Dunning, S Adjei, L Levin, AM Rohs, T Hilbert, E Borton, V Kapil, C Rice, GK Lemasters, and JE Lockey
J Occup Environ Med, April 25, 2012; .
OBJECTIVES:: To describe asbestos-related mortality among manufacturing workers who expanded and processed Libby vermiculite that contained amphibole fiber.
METHODS:: Standardized mortality ratio was calculated for 465 white male workers 31 years after last Libby vermiculite exposure. RESULTS:: Two workers died from mesothelioma, resulting in a significantly increased standardized mortality ratio of 10.5 (95% confidence interval, 1.3 to 38.0). These workers were in the upper 10th percentile of cumulative fiber exposure, that is, 43.80 and 47.23 fiber-years/cm, respectively. One additional worker with cumulative fiber exposure of 5.73 fiber-years/cm developed mesothelioma but is not deceased. There were no other significantly increased standardized mortality ratios.
CONCLUSIONS:: Workers expanding and processing Libby vermiculite in a manufacturing setting demonstrated an increased risk for the development of mesothelioma following exposure to the amphibole fiber contained within this vermiculite ore source.