Mining Contract: Advancing the Understanding of Respirable Silica Occurrence in Coal Mines

Contract #	75D30122C14433
Start Date	9/1/2022
Research Concept	Respirable silica dust (RS) remains a well-established occupational health hazard, and the percentage of its mass content in respirable coal mine dust (RCMD) has been monitored in U.S. mines for decades. However, the ongoing surge of RS-linked lung disease suggests that conventional monitoring does not yield sufficient understanding of health risks and that more insight is needed on the relevant characteristics of RS, particularly in relation to particle type. Different RS particle types can be present in the mine atmosphere, including independent particles and RS-containing micro-agglomerates (RSAs). Further, analytical capabilities to classify clusters of particles (i.e., agglomerates) have not been widely explored. Tools that will enable evaluation of both the exposure environment—via analysis of respirable mine dust samples—and the exposure outcomes—in situ analysis of respirable silica dust within the lung and its consequential burden—could prove to be especially valuable to the health and safety of miners.

Contract Status & Impact

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

This contract has three objectives, as follows:

Evaluate the relative abundance of RSAs and their characteristics (e.g., size, dispersibility) in RCMD.
Test the capabilities of advanced scanning electron microscopy with energy dispersive X-ray (SEM-EDX) tools for classification of RSAs and other micro-agglomerates.
Characterize RS particles in relation to such issues as size, occlusion, and association with other particles, in lung tissue specimens from coal miners with progressive massive fibrosis (PMF).

To achieve these objectives, three major focus areas will be considered. First, to evaluate RSAs in RCMD, researchers will use manual SEM-EDX, including both imaging and elemental mapping, to explore RSA characteristics. By analyzing particles directly on the sample filter, the goal will be to understand how these particles occur in the mine and how miners are likely exposed to them. Further, researchers will evaluate the relative dispersibility of RSAs, which may be important to fully understand exposure outcomes.

Second, advanced analytical tools such as computer-controlled scanning electron microscopy with energy dispersive X-ray (CCSEM-EDX) will be used to classify particles. While it is possible to investigate RSAs and other micro-agglomerates in RCMD using manual SEM-EDX methods, the key to success is to combine image analysis with elemental data on a per-particle basis. In addition, manual work is relatively slow and can only be done by an analyst with sufficient experience to interpret dust images and data. By contrast, automated techniques are much faster and might enable wider application with limited user bias, but only if they can be demonstrated to accurately classify micro-agglomerates.

Third, in situ analysis of RS particles in lung tissue affected by PMF will be undertaken. Opportunities to study the effects of real RCMD exposures are exceedingly rare, but, in addition to having lung tissues affected by PMF available to study, researchers under this contract have access to results from other projects where the density of mineral dust and relative abundance of RS particles were determined within PMF lesions. The results indicated more abundant RS in modern versus historical cases, with particularly high particle densities observed in many lesions. However, no attempt was made to look at other RS characteristics such as size, occlusion, and association with other particles, nor were particles at non-PMF areas examined for comparison. With researchers having access to tissue specimens for in situ automated particle analysis under this contract, new findings may offer important insights for disease pathology and help pinpoint causal RS characteristics.