[Solved] List the four major sources of occupational respiratory diseases. Ammonia: A colorless gas with a distinct sharp smell, commonly used in cleaning products and as a fertilizer, and also produced naturally in the human body. Bacteria: Microscopic, single-celled organisms found everywhere in the environment, which can be either beneficial or harmful to humans and other living beings. Occult Blood: Blood not visible to the naked eye, often detected in stool or urine samples to diagnose conditions such as gastrointestinal bleeding. Colon Cancer: A type of cancer that begins in the large intestine (colon), often detected through screening methods like colonoscopies.