New insights into rare earth element (REE) particulate generated by cigarette lighters: an electron microscopy and materials science investigation of a poorly understood indoor air pollutant and constraints for urban geochemistry

Cigarette smoking is a well-recognized cause of lung cancer and other diseases and is a major contributor to indoor air pollution in numerous settings worldwide. Most cigarette lighters use rare earth element (REE) mischmetal in their flints in order to aid ignition, and these lighters thus have pyrophoric properties. REE particulate emitted from these lighters presents a complexity in the role of health of smokers that has yet to be explored fully. Furthermore, these particles are likely present in numerous urban settings and contribute to the complexities of urban geochemistry. Details of the material properties of rare earth element (REE) particulate derived from smoking lighters are determined first the first time. Particulate was investigated using back-scatter detection scanning electron microscopy techniques and transmission electron microscopy techniques. Several particle types were observed and demonstrate a diverse range of size and textures, many of which are previously not documented and are much smaller than previous basic scanning electron microscopy investigations. These include irregularly shaped fragments of mischmetal, micrometer-scale spherules, aggregates of nanospherules, and platy sponge-like nanoparticles. All of these particles have significant REE content, and most are of a particle size that can be deposited deep in the lung. The available literature regarding toxicity of REEs and the material science data presented here argues very strongly for cause for concern.