The inhalation of asbestos fiber has been associated with cancer as well as with fibrotic diseases in the lung. Asbestos is not dangerous in its inert form, which is a rock-like mineral. However, when it is mined, milled, cut, disturbed, or used in other products, millions of microscopic fibers may be released into the atmosphere. These fibers, when inhaled into the lung, can cause irreversible injury.
Several diseases occur as a result of asbestos exposure. The most recognized are mesothelioma; asbestosis; pleural plaques; and lung, colon, and gastrointestinal cancers.
Asbestos is a mineral that is mined from rock and found in virtually every country in various concentrations. It is soft enough to be woven and is as flexible as cotton, yet it is fire-resistant and retains heat for insulation.
The ancient Greeks named the mineral asbestos, meaning inextinguishable. The Greeks and Romans also observed its harmful biological effects. The Greek geographer Strabo and the Roman naturalist Pliny the Elder both reported a sickness of the lungs in the slaves that wove asbestos into cloth.
Original uses for asbestos included making the wicks for the eternal flames of the vestal virgins, cloth for the funeral dress used at the cremation of kings, and napkins and tablecloths. The Romans would clean asbestos napkins by throwing them into a fire, and the asbestos cloth would amazingly come out whiter. The Romans named asbestos, amiantus, which means unpolluted.
Asbestos use declined in the Middle Ages, but it was rumored that Charlemagne had asbestos tablecloths. In the course of his travels, Marco Polo reported about articles made from asbestos cloth.
Asbestos use began to appear in historical writings again in the 1700s, and its use intensified with the advent of the Industrial Revolution. In industrial settings, asbestos-containing products were used for insulation for boilers, steam pipes, turbines, ovens, kilns, drywall products, and cements.
Malignant mesothelioma is a rare form of cancer that occurs in the lining of the lung (the pleura) or in the abdomen (the peritoneum). Mesothelioma is most often associated with exposure to asbestos. Scientists do not know the precise mechanism that causes mesothelioma. It is speculated that the asbestos fibers puncture the lining of the lung, become lodged in the pleura, and then the irritation creates the change in the cells that cause the mesothelioma.
Malignant mesothelioma is most often fatal, with most cases of the disease attributed to asbestos exposure.
Asbestosis is a scarring of the lung. It causes shortness of breath by blocking the transport of oxygen from the air in the lungs into the blood vessels that travel through the lungs. Oxygen can only cross the membranes of the lung if they are thin; asbestosis causes them to thicken. The degree of scarring determines the amount of shortness-of-breath that results. Some people can have mild scarring and have little loss of breathing capacity. Others with more of the disease get out of breath with mild exertion. As a general rule, the greater the exposure, the greater the risk of disease. Personal characteristics also appear to be a factor. Some people seem to form scars more easily, resulting in various levels of disease from the same exposure.
The scars are visible on x-rays in most cases. In the early stages of the disease, the scars can be so small that x-rays cannot detect them. There is a system of grading the degree of disease on x-rays, called the ILO classification. When physicians receive special training in this system, they are called B readers. The doctor scores each x-ray based on the type of scar, the extent of the scarring, and the density of the scars.
Pulmonary function testing can also detect the scars. Asbestosis makes the lung stiffer and smaller, decreasing the volume of air in the lungs. It also decreases oxygen transport as measured by the diffusion capacity.
Once scar formation takes place, it is irreversible. There is some disagreement in the medical community as to whether scarring continues to progress after exposure ceases. Because of the damage to the lungs, a person with asbestosis has an increased risk of getting lung infections and should get regular medical care and influenza vaccines.
Pleural plaques are scarring on the pleura (the outside lining of the lung). The majority of people with heavy exposure to asbestos develop pleural plaques.
The pleura is a thin lining that surrounds the lung. When inhaled, asbestos fibers travel to the outside of the lung and cause a scar in the lining. When they reach a certain size, the scars are visible on chest x-rays as a plaque. Alone, most of these plaques do not cause significant disability, but they do indicate that significant exposure has occurred, and that other asbestos-related diseases may be present. Calcified pleural plaques or extensive pleural thickening may encase the lung and result in a significant loss of lung function.
Lung cancer is a serious problem for people exposed to asbestos. Most lung cancer cases are found in people who also have a significant smoking history. Asbestos has a synergistic effect with cigarette smoke. Synergism refers to the multiplicative effect of asbestos exposure when combined with cigarette smoking.
Early studies by Dr. Irving Selikoff demonstrated that insulators who worked in the trade for 20 years and never smoked have a risk that is five times that of a non-asbestos worker. However, an insulator who did smoke has a 50- to 90-fold increase in risk. Evidence shows that if this insulator quits smoking, the risk of cancer falls over several years. Since the effect of asbestos inhalation is irreversible, one of the most important things any worker exposed to asbestos can do is to quit smoking.
Asbestos exposure is also believed to increase the risk of cancer of the larynx.
There are also higher rates of cancers of the gastrointestinal tract among asbestos workers. In people exposed to asbestos for more than 20 years, the rate of colon cancer increases by a factor of two. It is important for all workers exposed to asbestos to have regular check-ups with their doctors to look for early signs of colon cancer.
Asbestos-related diseases are dose-response diseases, which means they occur more frequently in heavily exposed populations.
The risk of disease will lessen as exposure decreases. Although used less now than in the past, asbestos is present in buildings constructed through the 1970s. It may still be used for brake and clutch linings and other products. Workers in buildings with asbestos insulation in place (on duct work, pipes, structural steel, or in roofing materials) must be aware of the special precautions needed for the handling of asbestos.
What is an asbestos screening?
An asbestos screening is a medical evaluation and educational session for a group of workers that have been exposed to asbestos.
Is an asbestos screening the same as a complete physical?
No. During a screening, each individual gets a brief physical examination. In the case of asbestos, the exam focuses only on the heart and lungs. A screening does not take the place of regular examinations with your private physician.
What else is included in an asbestos screening?
Each screening involves the brief physical exam and a review of the individuals medical and work histories as they relate to his or her exposure to asbestos. The screening also includes chest x-rays and spirometry tests, which measure lung capacity and function. The last part of the screening is an educational session about the potential health effects of asbestos and how to avoid future exposure. During the session, participants have the opportunity to ask questions about any other work hazards.
Are the test results confidential?
Yes. Each participant gets a personal letter with his or her individual results. The letter is not sent to anyone else without the individuals written permission.
What if the screening tests show a problem?
If the screening results show evidence of a possible asbestos-related disease, you should schedule an appointment with a board-certified pulmonologist who has experience in occupational diseases. We can provide the names of physicians with experience in evaluating and diagnosing asbestos-related diseases.