Asbestos is the name given to a group of naturally occurring silicates—chrysotile, amosite, crocidolite, tremolite, actinolite, and anthophyllite. Exposure to asbestos is a well-documented cause of pulmonary and pleural fibrosis, lung cancer, and mesothelioma, illnesses that may appear many years after exposure.
Mechanism of toxicity. Biopersistence in the lungs is a key property of inhaled asbestos fibers longer than 5 micrometers (shorter fibers are more easily cleared from the lungs) and is associated with induction of fibrosis, lung cancer, and malignant mesothelioma in rodent models. Exposure to long asbestos fibers has been shown to activate the epidermal growth factor (EGF) receptor and intracellular signaling pathways, leading to cell proliferation. Asbestos fibers have also been shown to interfere physically with the mitotic apparatus. Cigarette smoking enhances the risk for lung cancer in asbestos-exposed individuals.
Toxic dose. A safe threshold of exposure to asbestos has not been established. Balancing potential health risks against feasibility of workplace control, the current Occupational Safety & Health Administration (OSHA) federal asbestos standard sets a permissible exposure limit (PEL) of 0.1 fiber per cubic centimeter (fiber/cc) as an 8-hour time-weighted average. No worker should be exposed to concentrations in excess of 1 fiber/cc over a 30-minute period.
Clinical presentation. After a latent period of 15–20 years, the patient may develop one or more of the following clinical syndromes:
Asbestosis is a slowly progressive fibrosing disease of the lungs. Pulmonary impairment resulting from lung restriction and decreased gas exchange is common.
Pleural plaques typically involve only the parietal pleura and are usually asymptomatic but provide a marker of asbestos exposure. Rarely, significant lung restriction occurs as a result of severe pleural fibrosis involving both the parietal and visceral surfaces (diffuse pleural thickening).
Pleural effusions may occur as early as 5–10 years after the onset of exposure and are often not recognized as asbestos-related.
Lung cancer is a common cause of death in patients with asbestos exposure, especially in cigarette smokers. Mesothelioma is a malignancy that may affect the pleura or the peritoneum. The incidence of gastrointestinal cancer may be increased in asbestos-exposed workers.
Diagnosis is based on a history of exposure to asbestos (usually at least 15–20 years before the onset of symptoms) and a clinical presentation of one or more of the syndromes described above. Chest radiograph typically shows small, irregular, round opacities distributed primarily in the lower lung fields. Pleural plaques, diffuse thickening, or calcification may be present. Pulmonary function tests reveal decreased vital capacity and total lung capacity and impairment of carbon monoxide diffusion.
Specific tests. There are no specific blood or urine tests.
Other useful laboratory studies include chest radiography, arterial blood gases, and pulmonary function tests.
Emergency and supportive measures. Emphasis should be placed on prevention of exposure. All asbestos workers should be encouraged to stop smoking and observe workplace control measures stringently.
Specific drugs and antidotes. There are none.
Decontamination (See Decontamination)
Inhalation. Persons exposed to asbestos dust and those assisting victims should wear ...