What is the definition of asbestos?
Asbestos is a family of naturally occurring silica compounds (similar to, but not the same as, the silica of window glass and computer chips). These substances form fibers with varying shapes and sizes and are found throughout the earth. There are three commonly available types of asbestos:
- chrysotile (white asbestos),
- amosite (brown asbestos), and
- crocidolite (blue asbestos).
All three have been associated with cancerous and non-cancerous lung disease.
Asbestos has been used frequently in a variety of building materials for insulation and as a fire retardant, and in brake pads in cars. Today, it is found most commonly in older homes - in pipes, furnaces, roof shingles, millboard, textured paints, coating materials, and floor tiles.
What are the types of asbestos-related lung disease?
Lung disease from exposure to asbestos can be divided into three main types: 1) asbestosis, 2) disease of the lining of the lung (pleura), and 3) lung cancer.
- Asbestosis is a process of widespread scarring of the lungs.
- Disease of the lining of the lungs, called the pleura, has a variety of signs and symptoms and is the result of inflammation and the hardening (calcification) and/or thickening of the lining tissue.
- Lung cancer, either of the internal portions of the lungs or the outer lining (pleura).
All of the commonly available commercial forms of asbestos have been linked to cancerous and non-cancerous lung disease.
Asbestos-related lung disease occurred at very high rates toward the middle of the 20th century, when patients who were exposed decades earlier to asbestos eventually developed disease. British asbestos workers were among the first who were observed to have lung cancer related to asbestos.
Most current patients were once exposed to asbestos in:
- factories, or
- homes with asbestos, either in the process of carrying, installing, or removing asbestos, or while cleaning items laden with asbestos dust.
Some workers have been exposed to high concentrations of asbestos in:
- automotive repair,
- launderers of asbestos-containing clothing.
Continuing sources of exposure are asbestos removal and general construction industries. The delay between exposure to asbestos and the development of cancer can be anywhere from 10 to 40 or more years.
Despite not using asbestos in construction materials for the last 30 years, the number of deaths from asbestosis has increased over the past two decades. A 2009 study to assess the incidence of asbestos-related deaths concluded that the death rate is not expected to decrease sharply in the next 10 to 15 years. The World Health Organization reported in 2010 that more than 107,000 people die each year from asbestos-related lung cancer, mesothelioma, and asbestosis resulting from exposure at work.
Cases of asbestos exposure have been seen in the World Trade Center rescue and recovery workers.
What are the types of asbestos fibers?
There are two major groups of fibers, the amphiboles and chrysotile fibers. Chrysotile (white asbestos), also called "Serpentine" fibers, are long and curled. The amphiboles, long straight fibers (including actinolite, amosite, anthrophyllite, crocidolite, and tremolite) are much more likely to cause cancer of the lining of the lung (mesothelioma) and scarring of the lining of the lung (pleural fibrosis). Either group of fibers can cause disease of the lung, such as asbestosis.
The risk of developing asbestos-related lung cancer varies between fiber types. Studies of groups of patients exposed chrysotile fibers show only a moderate increase in risk. On the other hand, exposure to amphibole fibers or to both types of fibers increases the risk of lung cancer by two fold. Although the Occupational Safety and Health Administration (OSHA) has a standard for workplace exposure to asbestos (0.2 fibers/milliliter of air), there is debate over what constitutes a safe level of exposure. While some believe asbestos-related disease is a "threshold phenomenon," which requires a certain level of exposure for disease to occur, others believe there is no safe level of asbestos.
In most buildings, asbestos does not become airborne. However, surfaces that are damaged or disturbed can cause asbestos to become inhalable. High concentrations can occur after cutting, sanding, or remodeling asbestos- containing materials.
Reducing asbestos exposure involves either the removal or sealing of asbestos-containing materials. Inexperienced attempts to remove asbestos can release dangerous levels of the fibers.
What does fiber size have to do with asbestos-related lung disease?
Depending on their shape and size, asbestos fibers deposit in different areas of the lung. Fibers less than 3 mm easily move into the lung tissue and the lining surrounding the lung (pleura). Long fibers, greater than 5 mm (1/5 inch), cannot be completely broken down by scavenger cells (macrophages) and remain in the lung tissue. These asbestos fibers can cause inflammation. Substances damaging to the lungs are then released by the cells of inflammation that are responding to the foreign asbestos material. The persistence of these long fibers in the lung tissue and the resulting inflammation seem to initiate the process of cancer formation.
As inflammation and damage to tissue around the asbestos fibers continues, the resulting scarring can extend from the small airways to the larger airways and the tiny air sacs (alveoli) at the end of the airways. Some of these fibers can move to the surface of the lung where they form plaques (white-gray regions of scarred tissue) in the tissue lining of the lung (pleura). In severe cases of asbestosis, scarring of both the lung and its lining tissue can occur.
What is asbestosis?
Asbestosis is a process of lung tissue scarring caused by asbestos fibers. Because many other diseases also lead to lung scarring, other causes must be excluded first when a patient is found to have lung scarring (pulmonary fibrosis). Patients with particular X-ray findings or biopsy results must also have a remote history of asbestos exposure and a characteristically delayed development of the condition in considering asbestosis as a diagnosis. Smoking appears to increase the frequency and/or the rate of progression of asbestosis, possibly by preventing the efficient elimination of inhaled fibers from the airways.