# Mining Contract: Investigation of Respirable Mine Dust and Crystalline Silica Dust Characteristics and Toxicity in Metal/Nonmetal Mines

Keywords:Metal miningNonmetal miningRespirable dustSilica dust

| Contract #                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 75D30122C14685 |
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| 9/1/2022                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| Recent NIOSH-funded research on respirable coal mine dust (RCMD) has provided essential insights into the root causes of the prevalence of lung diseases among coal miners as well as the value of sampling techniques and real-time measurements. Researchers have focused on characterizing coal dust and silica dust in surface and underground coal mines, but less attention has been given to respirable dust and respirable crystalline silica (RCS) in metal and nonmetal (MNM) mines. Therefore, the physicochemical qualities and toxicity of mine dusts remain poorly understood, especially the size-related distribution of silica and other particle types and their associated toxicity. Detailed investigation of dust particle characteristics and toxicity will lead to an improved understanding of factors related to effective silica monitoring, dust control techniques, and the health effects of exposure to silica and other particles in MNM mines.

Respirable dust samples collected by the Mine Safety and Health Administration (MSHA) in U.S. MNM mines indicate that the percentage of RCS in the dust is generally higher in metal, sand, and gravel mines, with an increasing concentration trend over time. Further confounding the understanding of this issue, significant discrepancies have been reported between samples collected by mine operators and MSHA-collected samples. Among the possible explanations for these discrepancies are that operators collect multiple samples over consecutive work shifts, during which operating conditions may change, affecting the dust levels. Further, for various reasons, the incidence of respiratory disease associated with mine dust exposure for those working in in MNM mines is poorly tracked. To address these issues, the investigation of mine dust and RCS characteristics and toxicity is essential to fill a critical knowledge gap and ensure the health of MNM miners. |
| - Respirable Dust
- Respiratory Diseases                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |

## Contract Status & Impact

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

Under this contract, researchers will leverage resources from ongoing interdisciplinary collaborations, including mining engineering, environmental chemistry, and mineral processing, to investigate the characteristics and toxicity of mine dust and RCS in MNM mines. To achieve the overarching goal, two research aims will be pursued:
        - Conduct characterization studies (i.e., size, shape, surface area, mineralogy, elemental components) on mine dust and RCS samples of MNM operations.
        - Investigate MNM toxicity using simulated lung fluid and in vitro toxicity comparisons of respirable dust.

Broadly, the approach taken will be to investigate the toxicity of mine dust samples using simulated lung fluids and gastrointestinal fluids, lung tissues studies, and hydroxyl radical content analysis. Finally, researchers will conduct a size-dependent toxicological study (sub-micron vs. supra-micron) to better understand mine workers’ adverse health impacts and toxicity.

More specifically, researchers will conduct the comprehensive characterization studies by collecting respirable dust samples from at least six underground MNM mines (two metal and four aggregate operations) and use a combination of established techniques—mass-based methods for the size-related quantification of silica, and single-particle methods for both mass and number distributions of silicon-rich and other particle types.

To investigate MNM toxicity, the leaching capacity of metals and nonmetals from inhaled dusts that may be cleared to the gastrointestinal tract will be investigated using two simulated gastrointestinal fluids. The two fluids are simulated gastric fluid (SGF) and simulated intestinal fluid (SIF), which simulate the stomach environment and the human intestine conditions in the fasted state. Researchers will detect the dissolved species using high-performance liquid chromatography (HPLC) and quantify the dissolved silica and heavy metal fraction using inductively coupled plasma (ICP) spectroscopy.

The investigators will conduct the comprehensive comparison of the characterization and toxicity of RCMD (including RS) undertaken in a previous contract, with the results from this study conducted using dust obtained from MNM mines. The results will provide further insights on the root causes of a higher rate of lung diseases among coal miners and answer whether the current developing strategies for coal dust suppression and toxicity elimination can be potentially applied to MNM operations. Furthermore, the results of this comparison may shed further light on the effects of mine-specific parameters (i.e., mining method, fragmentation method, ventilation method, geometrical factors, equipment fleet, etc.) that may have any effects on the rate of lung diseases among miners. Assuming the characteristics and toxicity of RCS in MNM are not significantly different from the dust in coal mines, these parameters may be governing factors in the high rate of lung diseases in underground coal mines.

Overall, the research aim is to propose a size-dependent toxicological study—submicron vs. larger mine dust particles—to better understand mine workers’ adverse health impacts and toxicity. The final product will be a complete dataset to close a critical knowledge gap on the characteristics and toxicity of mine dust and silica dust in MNM mines. This will result in strategic approaches that can be taken to eliminate mining fatalities, injuries, and illnesses through relevant research. Ultimately, the characterization studies will provide detailed physiochemical characteristics of RCS in MNM mines.

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July 4, 2023

July 4, 2023

National Institute for Occupational Safety and HealthMining Program

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