What is the primary cause of pneumoconiosis?

Pneumoconiosis is primarily caused by the inhalation of various types of dust, with coal dust being one of the most significant sources. Specifically, coal dust exposure leads to a form of pneumoconiosis known as coal workers' pneumoconiosis, or "black lung disease." This condition occurs when coal dust particles are deposited in the lungs over time, leading to inflammation, fibrosis, and impaired lung function.

While other forms of pneumoconiosis can be caused by exposure to substances like asbestos or heavy metals, coal dust is the most prevalent cause associated with this disease in mining and industrial settings. Therefore, the primary cause of pneumoconiosis is correctly identified as coal dust exposure, as it directly relates to the most common form of this disease found in specific occupational environments.