We found that nanoparticles have the same toxicity as silica," Liu said. “Many think progressive fibrosis is from silica, but really the coal nanoparticles may also contribute to the toxicity. This is the first study of its kind to understand nano-particulate toxicity” https://sciencex.com/wire-news/445956602/particle-size-is-key-factor-in-coal-mining-related-respiratory-d.html