With every breath, we inhale gases, particles, and vapors. The lungs are the only internal organ that is directly exposed to the external environment. The primary purpose of the lungs is to maintain a proper balance of oxygen and carbon dioxide in the blood. While oxygen is necessary to respiration, various other inhaled substances are toxic to the lungs and can cause various pulmonary injuries.  Indeed, in excessive concentrations even oxygen can cause lung toxicity.

Every portion of the pulmonary system, from the trachea, to the bronchus, the bronchi, the bronchioles, and the alveoli is susceptible to injury from inhaled toxic agents. Among the respiratory diseases caused by inhalation of toxic chemicals are reactive airways disease (asthma), bronchitis, chemical pneumonia, and pulmonary fibrosis.

The effects of inhaled chemicals to the lungs depend on their physical and chemical properties, as well as host factors. Large particles cannot pass through terminal bronchioles and therefore cannot be inhaled into the alveoli, the delicate air sacs where gas exchange occurs. Thus, generally speaking, larger, soluble particles of toxic chemicals damage the upper airways, while smaller, less soluble particles more readily damage the alveoli. Alveolar damage is usually insidious, progressing from alveolitis (inflammation), to pneumonitis, on to irreversible and fatal interstitial lung disease.

Most minerals and metals are insoluble and remain in the lungs where they cause injury. Many gases and vapors are caustic or irritant, producing inflammatory responses in the lungs. These substances can injure the lungs even though they do not remain in the lungs after causing injury. Inhaled toxic substances can cause injury by a variety of mechanisms, including mechanical irritation, inflammation, immunologic or allergic response, and sensitization.

Among the occupational pneumoconioses (dust diseases caused by inhaled minerals) are silicosis, asbestosis, coal workers’ pneumoconiosis, and fibrous glass and other synthetic mineral fiber pneumoconioses. A long list of metals cause injury to the lungs, including aluminum, antimony, barium, beryllium, cadmium, cobalt, iron, mercury, silver, tin, titanium, tungsten carbide, and zirconium.  Among the gases that cause pulmonary injury are ammonia, chlorine, hydrogen sulfide, nitrogen oxides, ozone, phosgene, and sulfur dioxide.  Workers exposed to organic dusts in various agricultural trades can suffer from hypersensitivity pneumonitis and allergic lung diseases.

As new chemicals are manufactured and used, new pulmonary diseases are ascertained. As the only organ system exposed to the environment, the lungs are the first (and often the most sensitive) organ system at risk of chemically-induced injury. Indeed, in recent years, pesticides, cleaning agents, carpet and mobile homes have been recognized as causes of pulmonary disease.