A 60-year-old man has had worsening dyspnea and nonproductive cough over the past 2 years. On physical examination, his temperature is 37.4degC, pulse is 74/min, respirations are 20/min, and blood pressure is 110/70 mm Hg. A chest radiograph shows extensive interstitial lung disease and a prominent right-sided heart border. Spirometry reveals decreased FEV1 and FVC. His pulmonary disease is most likely caused by exposure to which of the following?

His pneumoconiosis (with progressive massive fibrosis) is producing restrictive lung disease. Silicosis occurs from prolonged and extensive exposure to inorganic dusts in occupations such as mining. Carbon monoxide poisoning produces hypoxemia without pathologic changes to lung tissues. Fungal hyphae may produce either an allergic response or a hypersensitivity pneumonitis. Plant pollens are most often associated with episodic atopic asthma. Sulfur dioxide contributes to chronic bronchitis. Wood dusts tend to produce bronchoconstriction.