Mining Contract: Characterization of Forms of Silica with Varying Degrees of Crystallinity in Respirable Dust to Assess their Effects on Miners� Pneumoconiosis

Contract #	75D30122C14876
Start Date	9/1/2021
Research Concept	Chronic exposure to excessive amounts of respirable crystalline silica (RCS) dust can lead to silicosis, a disabling and potentially fatal lung disease. Recent observations show an increased incidence of coal workers’ pneumoconiosis (CWP), progressive massive fibrosis (PMF), and other miners’ lung diseases, particularly among young miners in the Appalachian basin. Investigations have also revealed that cutting large amounts of rock to maintain haulage clearances increases the possibility for silica dust exposure. Despite helpful amendments to regulatory standards for RCS in 2016, the deterministic understanding of the silica or silica-containing dusts related to respirable diseases remains unclear, especially the relationship between characteristics of silica dusts and their toxicity. The current contract research aims to evaluate different forms of silica embedded in the mine-emitted dusts and how they are related to their host rocks’ mineralogical and geological features. This will explain the role of several forms of silica (crystalline and non-crystalline) in determining the overall toxicity of respirable dusts and could help reduce occupational exposure of workers, especially those involved in small/artisanal mining regions, stone mines, coal mines, and other commodities. Furthermore, a proper understanding of the forms of silica will benefit targeted control measures to eliminate the toxic fraction of the total silica, targeted development of personal protective equipment for workers in areas with high toxic silica content, and science-informed monitoring of systems for high toxic content.
Topic Areas	Respirable Dust Respiratory Diseases

Contract Status & Impact

This contract is ongoing. For more information on this contract, send a request to mining@cdc.gov.

Past research proves that different forms of silica have different degrees of crystallinity and crystal structures. This further suggests that shale samples (from strata where roof bolting occurs) include a considerable amount of silica-containing minerals, including quartz, illite, albite, and muscovite. Even though silica is abundant in these rock strata, the detailed composition of varying degrees of silicate minerals and their forms is unclear, which necessitates this contract research.

Under this contract, researchers will evaluate the presence and forms of silica in the respirable dust generated from various host rocks through an integrated experimental and field study program. The overall goal of this study is to characterize various forms of silica and provide statistically significant silica characteristics for future toxicity analysis. This goal will be achieved by pursuing three aims, as detailed below.

Collect representative floor and roof rock samples from different mines to prepare dust samples.
Characterize rock dust samples to understand their physical and compositional properties, including the proportion of crystalline and non-crystalline silica components.
Correlate what forms of crystalline of non-crystalline silica are related to different host rocks.

The subtasks related to achieving these three aims include collecting rock samples in the field and performing respirable dust generation in the lab, obtaining collected dust samples inspected by the Mine Safety and Health Administration (MSHA) and sorting the dust filters by different working environments for future analysis, characterizing the respirable dust generated in the lab, characterizing the physicochemical determinants of the toxicity of silica, characterizing the elongate particles present in the samples, and establishing a correlation between the host rock and the form of silica.

Successful undertaking of these tasks will require collaborations. Contract researchers have secured one industrial partner as a collaborator and two other coal mines have shown an interest in providing samples and stratigraphic information from their mines as well. Under this contract and based on past successes, further partnerships with northern and central Appalachian coal mines and a consortium of industrial mineral mining companies will be pursued.

The results from this research will lay the foundation for investigating the effect of non-crystalline silica in relation to its biological effects on lung cells. Knowing the forms of silica and their host rock will be highly beneficial in understanding the proper composition and nature of the respirable dust generated from different host rocks and mining operations. This will be crucial in determining the chemicals (surfactants) or additives for respirable silica dust control and their applicability for different types of silica content in the respirable dust, leading to possible additive combinations for different dust components. This could result in new application techniques for additives as well.

Ultimately, the outcomes of this research are not limited to the mining industry but will expand to other sectors and research efforts, including the glass and diatomaceous earth industry, artisanal miners, silica toxicologists, and volcanic ash toxicity analysis. Successful outcomes will also apply to the general population regularly impacted by silica exposure.