‘Black lung disease’, or coal workers pneumoconiosis (CWP), is typically caused by long-term exposure to coal dust.
Recently, researchers at the University of Illinois have been analysing coal miner morbidity between 1970 and 2016 and were intrigued to find that, where CWP was the cause of death, the highest proportion of cases was in participants born most recently (post-1940).
How so? Conclusions were presented at this year’s American Thoracic Society annual meeting.
The study population included 34,711 deceased miners, all of whom were listed on the National Institute of Occupational Safety and Health (NIOSH) National Death Index as having applied for federal benefits and contributed in the National Coal Workers’ Health Surveillance Program (CWHSP), as a result of suffering:
- Non-malignant respiratory diseases (NMRD);
- Pneumoconioses (excluding asbestosis), including CWP, silicosis and pneumoconiosis resulting from exposure to inorganic dusts;
- Chronic obstructive pulmonary disease (COPD), including emphysema;
- Lung cancer; and
- Ischemic heart disease (IHD).
N.B. For the sake of disease classification, pneumoconiosis and COPD both fell within the range of World Health Organisation (WHO) IDC-9 and IDC-10 codes that encompass NMRD. They are, to all intents and purposes, sub-types of NMRD.
Observed cases were first characterised by dates of birth. There were 4 ‘birth cohort’ categories, as follows:
- 1889 - 1919 (1st generation);
- 1920 - 1929 (2nd generation);
- 1930 - 1939 (3rd generation); and
- 1940 - 1970 (4th generation).
In addition to ‘birth cohort’ separation, the researchers also divided deceased coal miners by their ages at death:
- Less than 65-years-old;
- 65 - 74-years-old; and
- 75-years-old and above.
From the complete table of results, it can be inferred that the occupational health of coal miners has improved over time, as the number of applications for Black Lung Program benefits, at least for the most part, decreased from the 1st to the 4th generation:
- 1st generation – 7,368.5 cases (average per decade).
- 2nd generation – 10,910 cases (average per decade).
- 3rd generation – 4,887 cases (average per decade).
- 4th generation – 2,118.5 cases (average per decade).
Nevertheless, the researchers were more interested in the fluctuation of disease prevalence over time, i.e. proportional mortality.
While the proportion of IHD mortality was shown to have diminished over successive generations in each age bracket, the researchers intended to expose any disease types that had become increasingly prevalent over successive generations and provide some explanation why?
For workers between the ages of 65 and 74, it was identified that NMRD mortality constituted a higher proportion of overall mortality among those born after 1930 (28.3% and 31.5% in the 3rd and 4th generations, respectively) than those born prior to 1930 (15.0% and 18.5% in the 1st and 2nd generations, respectively).
COPD-related deaths followed the same pattern as NMRD cases. In 65 to 74-year-old workers, the proportion of deaths occurring in the 1st (6.7%) and 2nd (8.3%) generations increased significantly in the 3rd (12.0%) and 4th (13.4%) generations.
What is more, with regard to pneumoconioses, the other major NMRD sub-type, proportional mortality figures were significantly higher in 4th generation miners below the age of 65 (7.2%), compared to the older generations (between 3.8% and 4.8%).
According to the researchers, the mysterious proportional surge of pneumoconioses mortality in the youngest category of 4th generation miners may have been caused by a resurgence of progressive massive fibrosis (PMF) cases, which we previously eluded to in edition 221 of BC Disease News (here). PMF is the most severe form of CWP, which triggers sufferers to develop large masses in the upper regions of their lungs.
In another presentation at this week’s annual meeting, University of Illinois researchers have expanded on existing radiographic and pathologic evidence that suggests the underlying cause of growing PMF incidence may be excessive exposure to respirable crystalline silica (RCS), in an industry where extraction methods have had to evolve.
Lung tissue samples of 325 deceased miners, ‘who, if they started work at age 18 and had a 40 year career likely worked between 1903 and 1982’, were viewed under light microscopy to determine whether there had been a ‘historical shift in the type of PMF from classic coal mine dust associated disease towards a predominant silicotic form’.
In order to make this determination, the researchers categorised the samples as either ‘silicotic-type PMF’ (77), ‘mixed-type PMF’ (107), or ‘coal-type PMF’ (141).
However, the study authors arrived at the conclusion that, up until 1996, there was no statistically significant differences in the distribution of the samples, i.e. no discernible shift in PMF type.
Supplementary analysis of post-1996 tissue samples has been proposed to rule out the theory that there has been a ‘silicotic-type PMF’ shift in more recent years (up to 2016).
If long-term, excessive RCS exposure is proven to be principally responsible for causing modern-day coal workers’ PMF, then other labour forces may also be at high risk of the malignant disease. Who else? – the Institute of Occupational Health (IOSH) No Time To Lose campaign Factsheet lists the ‘main risk employment areas’:
- Abrasive blasting;
- Brick, concrete or tile manufacturing;
- Cement finishing;
- Ceramics manufacturing;
- Coke and other fuel manufacturing;
- Construction, cutting or grinding silica-containing material;
- Drilling silica-containing material;
- Electricity and gas supply;
- Glass manufacturing;
- Metals and machinery manufacturing;
- Mineral product manufacturing;
- Mining and quarrying;
- Steel manufacturing;
- Trades that use or fit plastic composite products; and
 Mia de Graaf, ‘Young miners are more likely to die of black lung disease than previous generations due to a mysterious rise in lethal form of the disease’ (20 May 2019 Daily Mail) <https://www.dailymail.co.uk/health/article-7049971/Young-miners-likely-die-black-lung-disease-previous-generations.htmlb> accessed 21 May 2019.
 K.S. Almberg et al., OCCUPATIONAL EXPOSURES INCLUDING DEPLOYMENT RELATED, MINING, AND AGRICULTURE. May 1, 2019, A2759-A2759 <https://www.atsjournals.org/doi/abs/10.1164/ajrccm-conference.2019.199.1_MeetingAbstracts.A2759> accessed 21 May 2019.
 R.A. Cohen et al., OCCUPATIONAL EXPOSURES INCLUDING DEPLOYMENT RELATED, MINING, AND AGRICULTURE. May 1, 2019, A2758-A2758 <https://www.atsjournals.org/doi/abs/10.1164/ajrccm-conference.2019.199.1_MeetingAbstracts.A2758> accessed 22 May 2019.