A study of nanoparticles : silica fume and woodsmoke

The research studies described herein were undertaken in order to characterize the particulate matter comprising the inorganic pollutant silica fume emitted by an electrometallurgical process and the organic emission of woodsmoke from residential woodheaters. These two emissions were selected in view of their suspected influential contribution to air pollution in Hobart, Tasmania, Australia. Their size characterization was seen as a necessary step for a better understanding of the nature of their toxicity within the human respiratory system. Their sizing was carried out using a Transmission Electron Microscope, the primary particle size (CMD) for 'silica fume being found to vary from a minimum of 34nm (0.034µm) to a maximum of 500nm (0.050µm) depending on sampling site at the smelter, while the aggregate size (VMD) varied from a minimum of 124nm (0.124µm) to a maximum of 180nm (0.18µm). Some 16,593 particles were involved. Sizes such as these place the primary particles of silica fume within the definition of nanometre particles. Similar results for the primary particles of silica fume have been recorded by other workers in the field when the technique of electron microscopy has been used. On the other hand, woodsmoke organics was shown to vary in primary particle size from a minimum CMD of 21nm (0.021µm) to a maximum of 23.5nm (0.023µm), depending on wood and heater type, while the aggregate size varied from a minimum VMD of 35nm (0.035µm) to a maximum of 58n (0.058µm). Similar sizes were found with a woodsmoke contaminated ambient air sample, with CMD for primary particles of 16run (0.016µm) and VMD for aggregates of 45nin (0.045µm). The woodsmoke sizing represented the analysis of some 10,194 particles and permits both the primary particles and almost all aggregates of woodsmoke to be defined as nanoparticles. This was in contrast to previous work in the field which was at least a factor of ten larger than the present study for both primary particles and aggregates, a fact which has raised come concern with regard to sizing limitations. Recent research has demonstrated the peculiarly high toxicity of particles in the nanometre size range. Other recent published work has postulated that this might explain the phenomena of health effects of nanoparticles on the human cardiopulmonary systems. It would seem, therefore, plausible to expect that the primary particles of silica fume and both the primary particles and aggregates of woodsmoke may subscribe to such hypotheses, being considered to be classified with the primary mediators of cardiopulmonary mortality and morbidity.