A 72-year-old man who works for a mine in Libby, Montana, has a clinical history of pulmonary function tests that show a decreased FEV1 and FVC, with a normal FEV1/FVC ratio. He dies and an autopsy is performed. The autopsy reveals a tumor in the right pleural cavity, which completely encases the lung. He also has tan-white pleural plaques in the right pleural cavity. Upon histologic examination of the lung, prominent alveolar septal fibrosis with honeycomb change is identified. This patient was most likely exposed to which of the following agents?

The correct answer is D.

The gross appearance of the tumor is consistent with a malignant mesothelioma. A pleural malignant mesothelioma is consistent with a history of asbestos exposure until proven otherwise. The pleural plaques are also an indication of asbestos exposure, and the histology of the lung and clinical testing is consistent with asbestosis.