Health Effects of Asbestos Exposure
Note: all have long latency periods; 15 to 40 years
[that is, the greater the exposure, and the longer the time of exposure, the greater the risk]
Asbestos Related Diseases
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.
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.
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.
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.
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.
Some health studies have observed increases in esophageal, stomach, colo-rectal, kidney, and possibly ovarian cancers as well as cancers in the nose and throat from exposure to asbestos. While the magnitude of increased cancer risk for these sites is not as great as for lung cancer and mesothelioma, the increased risk may be of considerable importance because of the high background rates of some of these tumors in the general population. By way of example, a 50% increase of risk in a common cancer such as colo-rectal cancer results in many more deaths than a similar 50% increase in a rare cancer.
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