Review Question - QID 210638

A 67-year-old man presents to his primary care physician because he has been feeling increasingly short of breath. Specifically, after retirement he has been going on daily morning walks with his wife; however, over the last year he feels that his endurance has decreased. His medical history is significant for well-controlled hypertension but is otherwise unremarkable. When asked, he reveals that he worked in a variety of industries throughout his life. Testing demonstrates decreased forced vital capacity (FVC) and a normal forced expiratory volume in 1 second (FEV-1) to FVC ratio. Pathology demonstrates changes primarily in the upper lobes where macrophages can be seen with dark round ingested particles. Which of the following is most likely associated with the cause of this patient's symptoms?