Asbestos is a naturally occurring mineral fiber. Basically, it's a rock. Essentially, there are six types, only three of which were used commercially. These are:
- Chrysotile or White Asbestos - The most common type in the U.S. , mined in Canada and previously mined in California. It is a serpentine structure, both wavy and hollow.
- Amosite or Red-Brown Asbestos - The name is derived from Asbestos Mines Of South Africa, it's place of origin. It is an amphibole structure, long straight solid rods.
- Crocidolite or Blue Asbestos - Only about 2-3% of the asbestos we encounter in this country is of the Crocidolite type. It is an amphibole structure very similar to Amosite, except for color. This mineral is mined in Australia.
The other three, which may be included in regulatory standards, are listed as tremolite asbestos, anthophyllite asbestos, and actinolite asbestos. All are fire resistant with high tensile strength and not easily destroyed or degraded by natural means. All are carcinogenic; that is, all have been shown to cause cancer of the lung and stomach, based on studies of workers. However, in order to be a health risk, asbestos fibers must be released from the material and be present in the air for people to breathe.
Dirty, contaminated air presents the greatest challenge to the respiratory system. To be a significant health concern, asbestos fibers must be inhaled. Some of the particles entering the airways reach the alveoli. When this occurs, white blood cells called macrophages attempt to engulf and digest the particles. In the case of asbestos, we are dealing with a mineral fiber, as a substance which macrophages can often not successfully attack. As a means of secondary defense, the macrophages deposit a coating on the fibers which are then deposited in the smaller passages. Here they clog and actually scar the tissues. The walls of the alveoli lose their elasticity and useful function in respiration. Coated asbestos fibers ("asbestos bodies") are often seen at autopsy.
Asbestosis is a disease which is characterized by pulmonary fibrosis, a progressive scarring of the lungs caused by the accumulation of asbestos fibers. Asbestosis is associated exclusively with chronic, occupational exposure. The build up of scar tissue interferes with oxygen uptake through the lungs and can lead to respiratory and heart failure. Often, asbestosis is a progressive disease, even in the absence of continued exposure. Symptoms include shortness of breath, cough, fatigue, and vague feelings of sickness. When the fibrosis worsens, shortness of breath occurs even at rest.
Of all the diseases related to asbestos exposure, lung cancer has been responsible for over half of the excess deaths resulting from occupational exposure. Although tissues and cells react to the presence of asbestos immediately, detectable symptoms take years, or more often decades, to manifest themselves. Asbestos-induced lung cancer may not show up on x-rays for twenty years or more after the exposure began. This delay between exposure and onset is referred to as the "latency period". Even in cases of prolonged heavy exposure, abnormalities commonly appear on x-rays only after ten or more years following exposure.
Asbestos as a Co-Factor: Other substances appear to cooperate with asbestos to multiply the risk of lung cancer. Asbestos exposure in combination with cigarette smoking can multiply the risk of developing lung cancer as much as ninety times over the risk to a non-smoker with no history of exposure to asbestos.
Asbestos is a term that refers to a group of naturally occurring fibrous minerals. Because of their resistance to decay and their remarkable insulating properties, asbestos fibers have been incorporated into thousands of products and materials. Unfortunately, it is now clear that exposure to airborne asbestos fibers can cause disease. The risk of developing asbestos-related disease varies according to the intensity, duration and nature of the exposure.
Asbestos related diseases are dose-response related. That is, the greater the exposure, and the longer the time of exposure, the greater the risk. Asbestos exposure can cause a number of disabling and fatal diseases. The principal rout of exposure is by inhalation through the nose and mouth. Asbestos, traditionally valued for it's indestructibility, is especially resistant to the internal defenses of the human body. Once lodged inside the lungs, most fibers will not break up or dissolve, and they cannot be neutralized or removed.
Mesothelioma, a malignant nodular type cancer of the membranes which line the lung cavity, is another disease related to asbestos exposure. Malignant mesotheliomas of these membranes (the pleura and the peritoneum) are extremely rare in persons with no history of asbestos exposure, but may account for 10% to 18% of excess deaths in workers exposed to asbestos. Generally, a latency period of at least 25 to 30 years is required in order to observe mesotheliomas, and some victims have had a latency period of forty years since their initial exposure to asbestos. This form of cancer is incurable and is usually fatal within a year after diagnosis. Mesothelioma has been associated with short term, incidental exposure, but here is no evidence of a relationship between cigarette smoking and mesothelioma risk.
Pleural plaques and pleural calcification are markers of exposure and may develop 10 to 20 years after initial exposure. Plaques are opaque patches visible on chest x-rays that consist of dense strands of connective tissue surrounded by cells. All commercial types of asbestos induce plaques. Plaques can occur even when fibrosis is absent and do not seem to reflect the severity of pulmonary disease.