A 78-year-old man has had increasing dyspnea without cough or increased sputum production for the past 4 months. On physical examination, he is afebrile. Breath sounds are reduced in all lung fields. A chest CT scan shows a dense, brightly attenuated pleural mass encasing most of the left lung. Microscopic examination of a pleural biopsy specimen shows spindle and cuboidal cells that invade adipose tissue. Inhalation of which of the following pollutants is the most likely factor in the pathogenesis of this mass?

Malignant mesothelioma is a rare tumor even in individuals with a history of asbestos exposure. The tumor may appear decades after exposure, and is not related to amount or length of exposure. Bronchogenic carcinoma is more common in individuals with asbestos exposure, particularly when there is a history of smoking. Bird dust inhalation can lead to hypersensitivity pneumonitis. Coal dust inhalation can lead to marked anthracosis, but without a significant risk of lung cancer. Inhalation of cotton fibers (byssinosis) leads to symptoms resembling asthma related to bronchoconstriction. Ozone and nitrogen oxides in smog can cause acute respiratory discomfort, but are not known to be promoters of neoplasia. Silicosis is typified by interstitial fibrosis and causes a slight increase in the risk of bronchogenic carcinoma.