While lung cancer appears to be the most common malignancy related to asbestos exposure, it is certainly not the only one. A rare cancer known as mesothelioma invades the thin lining surrounding the lung cavity. At least 50% of all cases studied have been related to asbestos exposures. Mesothelioma is usually associated with exposure to amphibole asbestoses, or with chrysotile contaminated with tremolite (a noncommercial amphibole form of asbestos). Other etiologic agents associated with malignant mesothelioma are therapeutic radiation using thorium dioxide, exposure to zeolite, a silicate in the soil, and possibly Simian virus 40.
Persons exposed to asbestos may develop an exudative pleural effusion 5 to 20 yr after exposure. Most often these are associated with asbestos exposures of 10 to 15 years. It has been suggested that the fibers migrate from the lungs to the pleura and induce an inflammatory response. Approximately 20% of individuals with evidence of exudative pleural effusion develop diffuse pleural fibrosis. A few may develop malignant mesothelioma many years later.
The malignant mesothelioma tumor is diffuse. It infiltrates the pleura, and is associated with pleural effusion. The associated fluid has a high concentration of hyaluronic acid. Peritoneal mesothelioma a less common mesothelioma attacks a thin membrane of mesothelial cells known as peritoneum, that envelops many of the organs in the abdomen. Peritoneal mesothelioma has been linked to asbestos exposure, but the route of entry of asbestos fibers into the peritoneum is still under investigation.
Asbestos related diseases are preventable. OSHA requires that employees and supervisors receive appropriate training if there is a potential of asbestos exposure in the workplace. It is most important that workers and supervisors understand conditions that might predispose individuals to asbestos particles (see the list of common occupations that are high risk for asbestos exposure). Air monitoring and testing of materials suspected of being contaminated is important to ensure the health of employees.
Exposure to suspected or known asbestos particles must be reduced to safe levels by mean of administrative controls, engineering controls and personal protective equipment. There has been a tremendous reduction in exposure to asbestos and incidence of asbestosis with the banning and removal of most forms of asbestos and advances in industrial hygiene practices.
It is of ultimate importance that employees who risk exposure to asbestos exposure abstain from smoking, since there is an unequivocal synergistic effect between asbestos exposure and smoking.
Employers must be vigilant to new possible sources of asbestos exposure. Tremolite asbestos contaminated vermiculite has been found in vermiculite ore mined in Libby, Montana. Some industrial grade talc has also been found to contain asbestos fibers.
While asbestos exposure is most often associated with the workplace, non-work related exposure has occurred. There are many documented cases of family members suffering from asbestos related diseases from exposure to asbestos from contaminated work-clothes brought home from the work place for laundering. Other non-work related exposure has been attributed to contaminated insulation and other building materials.
Education and vigilance are the keys to the prevention of asbestos related diseases.
Asbestosis: The most common disease associated with asbestos, asbestosis, is reported to develop in 49-52% individuals with significant industrial asbestos exposure, with a latency period of up to 45 years. After the first symptoms appear, asbestosis may lead to respiratory failure and death within 12-24 years. Respiratory failure may be accelerated by the development of Caplan's syndrome (Pneumoconiosis associated with rheumatoid arthritis); pulmonary hypertension; or malignancy, including lung cancer or mesothelioma.
No treatment for asbestosis is effective in curing the disease. Treatment emphasis is placed on preventing respiratory infections that might compound the problem, providing symptomatic relief, and slowing the progression of the disease.
Mesothelioma: Seven percent of workers exposed to asbestos will become affected with mesothelioma. It may take 24 - 40 years for the onset of symptoms, but once detected, the median survival time is between 4-12 months. Five percent of individuals with mesothelioma will survive three years, and five percent will survive for five years. There is presently no cure, but there are several options for treatment to slow progression of the disease including chemotherapy, radiation therapy and a combination of surgery, radiation therapy and chemotherapy.
Asbestos related lung cancer: An estimated 2% to 9% of lung cancers are related to occupational exposures. Most patients with asbestos related lung cancer will already have asbestosis when lung cancer is diagnosed. Lung cancer is highly lethal, with the highest recorded 5-year patient survival rates of 14% being observed in the United States. In Europe, the 5-year overall survival rate is 8%. Surgical resection is often successful treatment for lung cancer (stages I and II). Survival after resection has been reported to be as high as 70% at 3 years if caught in early stages, and 55% in more advanced cases.
While fewer and fewer workers are currently being exposed to asbestos, there will continue to be new cases of asbestosis, lung cancer, mesothelioma and less frequently encountered asbestos related diseases listed earlier in this article. There are countless workers who were exposed to asbestos before it was officially banned, and some workers continue to be exposed at some level. Asbestos exposure continues to be a problem in many other countries. Since the treatment of asbestos related diseases has not been very successful, the best strategy for dealing with the problem is to limit exposure. Such an effort requires vigilance on the part of employees and employers.
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Roberta C. Barbalace. Asbestos: A Manufacturing Health Hazard Dating to Prehistoric Times. EnvironmentalChemistry.com. Oct. 2004. Accessed on-line: 1/27/2022