Particle Characterization, Free Radical Generation, and Genotoxicity of Hard Metal and Detonation Coating Dusts

Abstract

Dust samples from sintering and detonation coating hard metal processes were characterized for composition (bulk, discrete particle and surface), generation of hydroxyl radicals in solution and micronucleus induction in vitro. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis were used to characterize discrete particle composition and elemental distribution. Electron spin resonance (ESR) was used to assay hydroxyl radical (HO·) spin-trap adducts. Post-detonation coating materials indicate that some particles contain substantial Cr and lesser amounts of other metals not present in the pre-coating materials. Post-detonation coating samples often had apparent surface Co and sometimes Cr on the tungsten carbide (WC) particles, as shown by elemental mapping of individual particles. This surface Co and Cr was not evident in pre-detonation samples or unsintered materials. ESR spectroscopy indicates that detonation-coating materials are capable of generating HO·, while the unsintered, WC and cobalt materials in this study did not. The overspray materials from the detonation-coating process produced 9-fold more HO· than pre-detonation samples, on a mass basis. Results suggest that elemental location and distribution, rather than composition alone, are important in explaining the differences in hydroxyl radical generation. Detonation coating materials and unsintered materials also showed differences in chemical pathways of HO· generation. Micronucleus induction was strongest for the post-detonation overspray, and comparable for the unsintered and pre-detonation materials. Overall, this study indicates there are substantial differences in the morphology, elemental distributions, chemical pathways of HO· generation and chromosomal damage induced by post-detonation materials, relative to either pre-detonation or unsintered hard metal process materials, and that these differences may be important in the hazard potential of these hard metal materials.