Because of its substantial tensile strength and fireproof characteristics, asbestos was used as a binder in siding cement up until 1973. The reason is because cement tends to be quite fragile at the ½” thickness required for such siding.
“Asbestos cement,” or cement asbestos siding, is a composite material made from Portland cement, sand and up to 10% asbestos. From the early 1960s onward, this was predominantly chrysotile; prior to that time, it was often the particularly deadly crocidolite or amosite variety. Because of this, cement plant workers employed prior to the mid-1970’s run an elevated risk of contracting asbestosis and mesothelioma.
The Difference Between Chrysotile and Crocidolite/Amosite
In terms of overall long-term health effects, there is little difference between serpentine (chrysolite) and amphibole asbestos fibers according to a medical study. A 1987 study of various cement plants in Louisiana showed a slightly higher rate of forms of asbestos cancer among workers at plants where amphibole asbestos was used than those at chrysotile plants (2.9% and 2.2% respectively); the material nonetheless presented a significant health risk in both cases.
Chrysotile asbestos is of a softer variety; such fibers are spring-shaped. Nonetheless, this substance was frequently contaminated with tremolite, another form of asbestos containing amphibole fiber. Amphibole asbestos fibers found in crocidolite and amosite resemble long, rigid needles when viewed under a microscope. Once inhaled or ingested, these “needles” burrow into the soft tissues.
Asbestosis is the result of microphages, or antibodies attacking these fibers as if they were a pathogen such as a virus. Because of the relative hardness and inorganic nature of these fibers (they are literally a form of stone), these microphages have little effect on them. Instead, they wind up being impaled upon these fibers; the digestive enzymes used to destroy viruses and bacteria escapes from the cell walls, acting like acid on the linings of the alveolar sacs of the lungs. This causes a build-up of scar tissue, which over the years reduces lung capacity until the victim literally suffocates.
The mechanism of malignant mesothelioma is less understood by medical researchers. It is known that because of their microscopic size, these sharp fibers can eventually burrow through the lungs into the pleural lining, and eventually reach any part of the body. Research seems to indicate that multiple factors come into play when it comes to this once rare form of cancer; asbestos fibers appear to interact with cells at the DNA level, causing them to become malignant. Medical researchers also suspect that a virus known as SV40 may play a part; this virus tainted some polio vaccines given between 1957 and 1963. In addition, chemical reactions may be responsible; it is estimated that smokers who are exposed to asbestos are 9000 times more likely to develop mesothelioma than non-smokers.
Mesothelioma is a cancer that attacks the outer lining of the lung, known as the pleura or mesothelium, which normally functions as a lubricating layer for the internal organs; on the lungs, it is known as pleural mesothelioma. Unlike most tumors, it grows in sheets, restricting the lungs’ ability to expand.