Efficacy of screens in removing long fibers from an aerosol stream – sample preparation technique for toxicology studies

Abstract

Fiber dimension (especially length) and biopersistence are thought to be important variables in determining the pathogenicity of asbestos and other elongate mineral particles. In order to prepare samples of fibers for toxicology studies, it is necessary to develop and evaluate methods for separating fibers by length in the micrometer size range. In this study, we have filtered an aerosol of fibers through nylon screens to investigate whether such screens can efficiently remove the long fibers (L >20 µm, a typical macrophage size) from the aerosol stream. Such a sample, deficient in long fibers, could then be used as the control in a toxicology study to investigate the role of length. A well-dispersed aerosol of glass fibers (a surrogate for asbestos) was generated by vortex shaking a Japan Fibrous Material Research Association (JFMRA) glass fiber powder. Fibers were collected on a mixed cellulose ester (MCE) filter, imaged with phase contrast microscopy (PCM) and lengths were measured. Length distributions of the fibers that penetrated through various screens (10, 20 and 60 µm mesh sizes) were analyzed; additional study was made of fibers that penetrated through double screen and centrally blocked screen configurations. Single screens were not particularly efficient in removing the long fibers; however, the alternative configurations, especially the centrally blocked screen configuration, yielded samples substantially free of the long fibers.

• Aerosol
• fiber length
• glass fiber
• nylon mesh screens
• vortex shaker

Acknowledgements

The authors thank Mariko Ono-Ogasawara (Japan National Institute of Occupational Safety and Health, and Japan Fibrous Material Research Association, JFMRA) for the samples of the GW1 glass fibers used in this study. We thank Joe Fernback (NIOSH), for SEM images, and Elizabeth Ashley (University of Cincinnati), for assisting in the analysis of PCM images of the fibers. We thank Pramod Kulkarni and Chaolong Qi for helpful discussions. We thank the referees of the initial version of our manuscript for prompting the discussion contained in the Appendices. We thank the referee of the revised manuscript for the fiber inertia argument (“Discussion” section), rationalizing the efficacy of the centrally blocked screen configuration.