Physical and chemical characterization of McIntyre Powder: An aluminum dust inhaled by miners to combat silicosis

Abstract

McIntyre Powder (MP) is a finely ground aluminum powder that was used between 1943 and 1979 as a prophylaxis for silicosis. Silicosis is a chronic lung disease caused by the inhalation of crystalline silica dust and was prevalent in the Canadian mining industry during this time period. The McIntyre Research Foundation developed, patented, and produced the MP and distributed it to licensees in Canada, the United States, Mexico, Chile, Belgian Congo, and Western Australia. In the province of Ontario, Canada it is estimated that at least 27,500 miners between 1943 and 1979 were exposed to MP. The present study was undertaken to examine the chemical and physical characteristics of two variations of MP (light grey and black). Chemical analyses (using X-ray Fluorescence and Inductively Coupled Plasma approaches) indicate that the black MP contains significantly higher concentrations of aluminum and metal impurities than the light grey MP (p < 0.001). X-ray diffractometry shows that while aluminum hydroxide dominates the aluminum speciation in both variations, the higher total aluminum content in the black MP is attributable to a greater proportion of elemental aluminum. Physical characterization (using electron microscopy, light microscopy, and dynamic light scattering) indicates that the light grey MP consists of particles ranging from 5 nm to 5 µm in diameter. Atomic Force Microscopy shows that the light grey MP particles in the nanoparticle range (<100 nm) have a mode between 5 and 10 nm. Consequently, it is possible that inhaled smaller MP nanoparticles may be transported via blood and lymph fluid circulation to many different organs including the brain. It is also possible for inhaled larger MP particles to deposit onto lung tissue and for potential health effects to arise from inflammatory responses through immune activation. This MP characterization will provide crucial data to help inform future toxicological, epidemiological, and biological studies of any long-term effects related to the inhalation of aluminum dust and nanomaterials.

Keywords:

• Aluminum
• aluminum inhalation
• McIntyre Powder
• nanoparticles
• occupational exposures
• particle characterization

Acknowledgments

We are grateful to Janice Martell, founder of the McIntyre Powder Project, for her unwavering support and wealth of knowledge and for supplying samples. We would also like to thank Dave Wilken and Kimberly O’Connell from OHCOW for their support and for supplying samples. We would also like to thank Michelle Kelvin from XPS Glencore, Canada for conducting the XRD analysis. We are grateful to Christine Levesque and Marc Chénier of Health Canada for conducting the ICP analyses, and we thank Kristin Macey, Larbi El Bilali, and Daryl Smith of Health Canada for valuable review comments on an earlier version of the manuscript. We are also grateful to Loïc Hamon of SABNP laboratory at Évry University, Paris, France for conducting the AFM analysis. We thank Mohamed Sennour from Centre des Matériaux of MINES Paris Tech, Évry, France for the TEM analysis. Mitacs, NSERC, and Bruce Power had no role in the preparation of this article.

Additional information

Funding

Funding for this study was provided by Bruce Power (contract #00209094), Mitacs (IT03934), and NSERC (RGPIN/6700 2015).