Coal Dust Key Culprit in Miners' Emphysema

Breathing coal dust worsens emphysema independently of cigarette smoking, suggest results of a study published this month.

The current findings, are particularly relevant today given the boom in coal production and the millions of people who are still being exposed to high levels of coal dust, Dr. Benoit Nemery, of Katholieke Universiteit Leuven in Belgium, who was not involved in the study, notes in commentary published with the study.

While several studies have linked exposure to dust on the job to obstructive lung disease, there remains a common belief that these illnesses, including emphysema, are mainly due to cigarette smoking.

To investigate the role of coal dust in emphysema, Dr. Eileen D. Kuempel, of the National Institute for Occupational Safety and Health (NIOSH) in Cincinnati and colleagues looked at lung tissue from 616 coal miners and 106 non-miners who died between 1957 and 1978.

In emphysema, the air sacs at the ends of the tiniest breathing tubes are gradually destroyed, so less oxygen is able to reach the blood stream, while inhaled air gets trapped within the lungs. As the disease progresses, large holes develop in the lung tissue and breathing becomes more and more difficult.

Kuempel's team found that cumulative exposure to breathable coal mine dust was a highly significant predictor of more severe emphysema, after accounting for cigarette smoking, age at death, and race.

Emphysema was much more severe in miners than non-miners among both smokers and non-smokers. Not surprisingly, emphysema was also more severe among smokers than among people who had never smoked cigarettes.

The researchers also found that greater concentrations of coal dust in lung tissue correlated with more severe emphysema.

While the current study looked at people who had worked as coal miners before the US began enforcing a 1972 law limiting the amount of coal dust exposure on the job to 2 milligrams per cubic meter, Kuempel and her team say, people who spend a lifetime working in the industry, even under the new standard, would be exposed to amounts of coal dust similar to those breathed by the miners in the current study.

This provides more evidence, the researchers say, that regulators should adopt NIOSH's recommendation to reduce the coal dust exposure standard for miners to 1 milligram per cubic meter.

Ninety percent of the 7 million people working in the coal industry worldwide are employed in developing countries, Nemery writes in his editorial, where they may be exposed to much higher levels of coal dust.

"The environmental and climatic impacts of burning coal are, quite rightly, a source of concern," he says. "However, the direct consequences of extracting coal on the health of millions of coal miners must be an equal concern. The strong findings of Kuempel and colleagues should serve as a useful reminder of this reality."