Toxicity of respirable coal dust: An overview of origin, chemistry, mechanisms, and possible remedies

The prevalence of coal workers' pneumoconiosis (CWP) has been on the rise among U.S. coal miners since the early 2000s and is most pronounced in central Appalachia. Such adverse effects on human health are partly linked to the toxicity of respirable coal mine dust particles. In this review, we present an overview of the characteristics and health effects of the coal dust components, as well as the origin, chemistry, and mechanisms for their potential toxicity. Toxicity of coal mine dust is linked to the surface chemistry and bioactivity of the composing particles, such as coal, crystalline silica (quartz), pyrite, and sometimes diesel particulate matter. Formation of reactive oxygen species, such as •OH on the surface of these particles, contributes to the toxicity of coal dust. Various mechanisms including the metal-micelle coating, polymer-coating, chelation of the surface metal ions, and surface silanization, have been proposed in previous studies for the reduction or inhibition of the toxicity of coal dust particles. However, due to the complexity in surface chemistry of the various minerals and coal, there is no single universal detoxification mechanism for coal dust. One feasible remedy to address the proposed mechanisms of toxicity is the use of chemical additives as wetting agents. Important considerations for this approach include particle size and aging, mineralogy, morphology, chemical composition, solubility, surface charge, and synergistic effects of the composing phases. Additional factors to consider are the solution quality and composition, coal rank, and the potential hazards and costs associated with the chosen chemical agents.