Non-quartz part of coal might turn the coalminer's lungs to black

Perhaps it's the American bluegrass singer Hazel Dickens who most poignantly voiced the burden of the coal miner when she sang: he's lived a hard life and hard he'll die / black lung's done got him, his time is nigh. While the plight of the coal miner has often been sung, it has also raised the attention of scientific researchers. What, for example, is exactly the relation between coal and interstitial lung disease (ILD)?

The 'black lung' from the eponymous harrowing song by Dickens is medically known as 'coalworker's pneumoconiosis', a form of ILD which literally turns the lungs black from their usual pink color. While the development of lung diseases caused by exposure to coal dust and coal impurities like quartz and iron has already been studied extensively over the last century, it is still not clear what components of the coal dust are actually responsible for disease development. While previous studies mostly focussed themselves on quartz, (an important fibrogenic component of coal), there were presently no systematic reviews on the non-quartz part of coal and development of lung diseases.

Danish researchers therefore aimed to systematically review what is known about the relation between exposure to the non-quartz part of coal dust and ILD. With a systematic review they identified 2945 articles. With strict eligibility criteria, concerning the ‘pure coal effect’, they came to the inclusion of only nine studies. Among these nine studies six studies indicated an independent effect of the non-quartz part of coal on the development and progression of ILD, two did not demonstrate an effect and one was inconclusive. The researchers conclude that although they did find an independent effect of non-quartz coal dust on the development of ILD, there were also a lot of methodological limitations in their study. 

Maybe when this follow-up analysis is done, songs like 'Black Lung' can be updated

In order to strengthen the evidence, well conducted follow-up analyses on workers exposed to coal dust with no or very low mineral content are needed, according to the Danish scientists. Maybe when this follow-up analysis is done, songs like 'Black Lung' can be updated with a more specific mentioning of the particles causing all this misery, although it is doubtful whether the poor miners will find much solace in these findings. 

References:
Christiane Beer, Henrik A. Kolstad, Klaus Søndergaard, Elisabeth Bendstrup, Dick Heederik, Karen E. Olsen, Øyvind Omland, Edward Petsonk, Torben Sigsgaard, David L. Sherson & Vivi Schlünssen (2017) A systematic review of occupational exposure to coal dust and the risk of interstitial lung diseases, European Clinical Respiratory Journal, 4:1, 1264711

Song from Hazel Dickens on youtube: https://www.youtube.com/watch?v=5hvLoEcLBf0