Block 5: Silicosis and Coal Workers’ Pneumoconiosis - Coal Dust And The Reaction Of The Lung To Retained Coal Dust.

COAL DUST AND THE REACTION OF THE LUNG TO RETAINED COAL DUST:

• Coal dust is less toxic than crystalline silica.
• Silica content of coal dusts vary. Most are < 5%. High silica dusts, for example, in rocks comprising the coal overburden, mean that coal workers are also at risk of silicosis.
• Coal dusts also vary according to conditions of temperature and pressure under which the coal is formed:
  • Low rank = bituminous;
  • High rank = anthracite;
  • Harder, high rank coals appear more pathogenic than low rank coals.
• Coal dust particles, like other particles attract alveolar macrophages once they have been deposited in the alveoli.
• The inflammatory response provoked is less intense than with silica and there is less collagen in the resulting nodules, which in CWP are termed macules in their early stages.

Coal dust macules and nodules, illustrated above, are less distinct than silicotic nodules. They also have very obvious carbon deposition thus giving CWP its alternative name "Black Lung".

Total coal dust retained by the lung is the most important determinant of the appearance of radiological CWP. The figure on the right shows the risk or probability of different categories of CWP in persons exposed to the dust levels stated along the x-axis for a 40 year working lifetime.

Pathologically the conditions are distinct but radiologically they are similar. In CWP nodules tend to be smaller (p sized) and radiological signs of COPD may be present. In the table below, there is a simple summary of the health effects of silica and coal dust.