Remember the small giants - Occupational exposure and characterization of aerosol particles

Abstract: BACKGROUND: Exposure to airborne particles in occupational environments can lead to both acute and long-term health effects in humans. To date, particle exposure limits in the air are typically given in terms of mass concentrations. But by only using mass concentration to characterize particles means there is a risk that other relevant characteristics, such as particle size and composition are concealed. This is argued to be the case for exposure to engineered nanoparticles (ENP), which are particles tailored to possess unique properties. The aim of this thesis is to provide knowledge to improve the characterization and risk assessments of particle emissions in selected occupational environments. METHODS: 1) In a diesel exhaust exposure chamber study, several techniques were combined to determine a wide range of particle characteristics, including particle number, surface, mass, chemistry and morphology. 2) In a hairdresser exposure chamber study, the emissions of particles and persulfate salts during hair bleaching were characterized. 3) In two field studies, the emissions of ENPs in two different production facilities were characterized by filter sampling and by direct reading instruments. A laser vaporization aerosol mass spectrometer (LV-AMS) was used for both selective sampling of emitted particles based on their composition, and for in-situ analysis of ENPs inside the production line. RESULTS: 1) If diesel exhaust particles are assumed to be spherical, the estimated particle mass concentration from number concentration was overestimated by 261% compared to if their aggregated structures were considered. 2) During the application of hair bleaching, large particles (> 10 µm) were emitted from both bleach powder that was classified as dust-free and powder that was not. 3) Particles emitted during the maintenance of ENP production equipment were predominantly highly agglomerated with nanostructured surfaces, consisting of nanoparticles grown together to larger scales (> 1 µm). With the LV-AMS, emissions were correlated to specific particle types and interferences from background particles could be avoided. CONCLUSIONS: The ability to compare different diesel exhaust exposure studies will increase if methods are utilized that allow the characterization of particle size, shape, morphology and chemistry and that include different concentration metrics. Exposure assessments of ENP production facilities and hairdresser salons should include methods for coarse particle sampling. LV-AMS is a promising method for selective sampling of emitted particles in occupational environments, and for in-situ analysis of particle production. But the LV-AMS’s cost efficiency, practicality, and capability to sample coarse particles need to be extended. Accurate exposure assessments should cover a wide particle size range in order to find the nanoparticles that hide in the form of bigger particles.