Influence of instruments performance and material properties on exposure assessment of airborne engineered nanomaterials

Over the last decades, materials engineered of nanosized structures have increased tremendously, in terms of both produced tonnage and economic market share. This, together with the fact that some of these engineered nanomaterials have shown an increased toxicological effect in humans as compared to their bulk counterpart, has expanded the scientific field of exposure measurements to airborne nanoparticles. As the greatest potential for human exposure to engineered nanomaterials resides within the production, packaging and downstream powdermaterial handling, as well as at reworking/waste treatment facilities, exposure risk for workers has received great focus.
The studies described in this thesis come to four main conclusions: 1) Mass-balance modeling of airborne engineered nanomaterials using dustiness index as a primary source term can be useful for assessment of material-specific exposure scenarios and in decision-making regarding powder choices. 2) That such mass-balance modeling can, however, be highly sensitive to environmental
conditions, especially humidity, during storage and use, which may cause a severe misrepresentation of the true emission if the conditions during dustiness testing differ from the modeled scenario. 3) That particles with a geometrical mean diameter above 200 nm cannot be measured reliably with the Fast Mobility Particle Sizer (FMPS 3091, TSI Inc., MN, USA) but will instead be underestimated in terms of particle size and overestimated in terms of particle number concentration. Measured size distributions with particle modes above 150 nm should not be deemed reliable as they might arise from misclassification of larger size particles. 4) That current methods for real-time measurement of lung-deposited surface area concentration for airborne engineered nanomaterials are cannot be relied upon to represent comparable levels for use in exposure assessments and for other regulatory purposes.
The work presented in this thesis provides understanding to improve assessment of airborne exposure to engineered nanomaterials in occupational settings. Based on conclusions drawn in this thesis, exposure assessment and control-banding models should review their use of dustiness index as a term of emission or ensure that the specific material of interest has been tested in relevant conditions. The work shows the limits of the capabilities of current techniques for
measurement of airborne particle characteristics, and highlights necessary improvements for future adaptions of new metrics into regulatory testing and occupational exposure limits.