A 35-year-old male factory worker in Mumbai presents with progressive dyspnea, chest tightness, and a dry cough of 8 months' duration. He has worked in a textile mill for 12 years, where he is exposed to cotton dust without adequate respiratory protection. Chest X-ray shows bilateral lower lobe fibrosis. Pulmonary function tests reveal a restrictive pattern. His coworkers in the same department also show similar radiological findings. Which component of the epidemiologic triad is BEST represented by the factory environment and lack of protective equipment in this case?