CHRYSOTILE
General Information
| Mainterm | CHRYSOTILE |
| CAS Reg.No.(or other ID) | 12001-29-5 |
| Regnum |
177.2600 |
From www.fda.gov
Toxicity Profile
| Route of Exposure | Inhalation ; injection |
|---|---|
| Mechanism of Toxicity | When asbestos fibers are inhaled, many are deposited on the epithelial surface of the respiratory tree. Fibers that are retained in the lung or mesothelium for long periods of time are capable of producing chronic inflammation and fibrotic and tumorigenic effects. These effects may be mediated by direct interactions between the fiber and key cellular macromolecules, or they may be mediated by the production of reactive oxygen species and other cellular factors originating from alveolar macrophages. In addition, the physical-chemical nature of the fiber appears to be an important determinant of toxicity. It is generally agreed that exposure to amphibole fibers can produce mesothelioma, and that the potency of amphibole fibers to produce mesothelioma is greater than that of chrysotile. Asbestos fibers can adsorb to a variety of cellular macromolecules (e.g., proteins,membrane lipids, RNA, DNA). The coulombic forces between the asbestos fiber and some of these macromolecules may induce conformational changes, and these changes could affect protein function and chromosomal fidelity. Chrysotile fibers were found to bind to cytochrome P-450, thereby decreasing mono-oxygenase activity. Chrysotile and crocidolite fibers were also found to bind to artificial lipid membranes in vitro, thereby increasing membrane rigidity. Fibers found to be translocated near the nucleus can interact with the cytoskeleton and interfere with chromosome segregation. |
| Metabolism | Asbestos fibers are not metabolized in the normal sense of the word, and amphibole fibers that are retained in the lung do not appear to undergo any major changes. However, chrysotile fibers appear to undergo some type of breakdown or alteration in the lung. Some of the fibers will be deposited in the air passages and on the lung cells. Most fibers are removed from the lungs by being carried away or coughed up in a layer of mucus to the throat, where they are swallowed into the stomach. Fibers that are deposited in the deepest parts of the lung are removed more slowly. In fact, some fibers may move through the lungs and can remain in place for many years and may never be removed from the body. Longer fibers that are retained in the lung may undergo a number of processes including translocation, dissolution, fragmentation, splitting, or protein encapsulation. Long fibers that reside in the lung can become encapsulated in protein, forming what is often referred to as an "asbestos body". In response to asbestos fibers, alveolar macrophages produce reactive oxygen species in an attempt to digest the fiber. The reactive oxygen species include hydrogen peroxide and superoxide radical anion (O2-). Fibers that have been swallowed (those present in water, or those moved to the throat from the lungs) almost all pass along the intestines within a few days and are excreted in the feces. |
| Toxicity Values | |
| Lethal Dose | |
| Carcinogenicity (IARC Classification) | 1, carcinogenic to humans. |
| Minimum Risk Level | |
| Health Effects | Infected people develop a slow buildup of scar-like tissue in the lungs and in the membrane that surrounds the lungs, so breathing becomes difficult. Blood flow to the lung may also be decreased, and this causes the heart to enlarge. This disease is called asbestosis. Infected people have increased chances of getting two principal types of cancer: cancer of the lung tissue itself and mesothelioma, a cancer of the thin membrane that surrounds the lung and other internal organs. The cellular immune system of the patient can be depressed. Also, deletions of chromosome segments have been noted in human mesothelioma cells or cell lines. (L222) |
| Treatment | In vitro studies have shown that the effects of asbestos can be diminished by compounds that reduce the levels of reactive oxygen species, such as free radical scavengers (ascorbic acid, bemitil, mannitol, salicylate, 5,5'-dimetyl-l-proline N-oxide, rutin, vitamin E, vitamin A) and enzymes that catalyze the decomposition of reactive oxygen species (catalase, superoxide dismutase). Patients should quit smoking, perform bronchial drainage and can use chest physical therapy techniques to further aid in removing secretions. Shortness of breath is treated with bronchodilators, inhaled or oral medications that open up the bronchial tubes and allow the passage of air. In more severe asbestosis cases, supplemental oxygen may be required. Productive cough is treated with humidifiers and chest percussion. Asbestosis can be treated, but not cured. |
| Reference |
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From T3DB