Asbestos as carcinogenic material
Asbestos is a group of naturally occurring silicate minerals characterized by long, thin fibers. It has long been recognized as a carcinogenic material, with significant health risks associated with prolonged exposure. The U.S. government classified asbestos as a carcinogen under the Clean Air Act of 1963, leading to a ban on its manufacture and distribution in 1990. Various forms of asbestos, such as chrysotile and crocidolite, have been widely used in construction and industrial products due to their heat resistance and strength. However, inhaling asbestos fibers can lead to serious health issues, including mesothelioma and lung cancer, with symptoms often manifesting decades after exposure. While studies indicate that the amphibole forms of asbestos are particularly hazardous, chrysotile's risks remain debated. The U.S. Environmental Protection Agency has concluded that there is no safe level of asbestos exposure, although the Occupational Safety and Health Administration permits limited exposure in occupational settings. Recent events, such as the exposure of recovery workers during the World Trade Center cleanup, have highlighted the dangers of even brief encounters with asbestos, raising concerns about its ongoing impact on public health.
Subject Terms
Asbestos as carcinogenic material
DEFINITION: Industrial term for certain silicate minerals that occur in the form of long, thin fibers
The adverse health effects of breathing high concentrations of asbestos over prolonged periods have been known since the early 1970. The federal Clean Air Act of 1963 classified asbestos as a carcinogenic material, and in 1990 the US Environmental Protection Agency established a broad ban on the manufacture, processing, importation, and distribution of asbestos products.
Asbestos-form minerals are natural substances that are common in many types of igneous and metamorphic rocks found over large areas of the earth. Erosion continually releases these fibers into the environment, and most people typically inhale thousands of fibers each day, or more than 100 million over a lifetime. Asbestos fibers also enter the body through drinking water. Drinking-water supplies in the United States typically contain almost 1 million fibers per quart, but water in some areas may have as many as 100 million or more fibers per quart.
Properties
Many silicate minerals occur in fibrous form, but only six have been commercially produced as asbestos. In order of decreasing commercial importance, these are chrysotile (white asbestos), crocidolite (blue asbestos), amosite (brown asbestos), anthophyllite, tremolite, and actinolite. All these minerals except chrysotile are members of the amphibole group of minerals, which have a chainlike arrangement of atoms. In contrast, chrysotile, as a member of the serpentine family, has atoms arranged in a sheetlike fashion.
Although the individual properties of these minerals differ greatly, they share several characteristics that make them useful and cost-effective. These include great to heat, flame, and acid attack; high tensile strength and flexibility; low electrical conductivity; resistance to friction; and a fibrous form, which allows them to be used for the manufacture of protective clothing. Asbestos thus was widely used until the 1970s in a great variety of building and industrial products. Such common materials as vinyl floor tiles, appliance insulation, patching and joint compounds, automobile brake pads, hair dryers, and ironing board covers all might have contained asbestos. Most such products now contain one or more of several substitutes for instead of asbestos itself. However, many of the substitutes may not be hazard-free, a fact that is starting to be recognized by legislators. For example, in 1993 the World Health Organization (WHO) stated that all substitute fibers must be tested to determine their carcinogenicity. Germany now classifies glass, rock, and wools as probable carcinogens. In 2024, the US Environmental Protection Agency (EPA) began prohibiting the importation of chrysotile asbestos. This means that this type of asbestos, which was the only form being imported, can no longer be processed and distributed in the United States.
Health Effects
The US Department of Health and Human Services classifies asbestos as a carcinogen. Studies leading to this determination were mostly based on asbestos workers who had been exposed to extremely high levels of fibers for many years. These studies concluded that the asbestos workers had increased chances of developing two types of cancer: mesothelioma (a cancer of the thin membrane surrounding the lungs) and cancer of the lung tissue itself. These workers were also at increased of developing asbestosis, an accumulation of scarlike tissue in the lungs that can cause great difficulty in breathing and permanent disability. None of these diseases develops immediately; all have long periods, typically fifteen to forty years. Contrary to common misconception, to asbestos does not cause muscle soreness, headaches, or any other immediate symptoms. The effects of asbestos exposure typically are not noticed for many years.
It is generally agreed that the risk of developing disease after asbestos exposure depends on the number of fibers in the person’s body, how long the fibers have been in the body, and whether the person is a smoker, since smoking greatly increases the risk of developing disease. There is no agreement on the risks associated with low-level, nonoccupational exposure. The US Environmental Protection Agency (EPA) has concluded that there is no safe level of exposure to asbestos fibers, but the Occupational Safety and Health Administration (OSHA) allows up to 0.1 fiber per cubic centimeter of air during an eight-hour workday.
Other Controversies
Another area of controversy stems from scientific studies showing that all forms of asbestos are not equally dangerous. Evidence has shown that the amphibole forms of asbestos, and particularly crocidolite, are hazardous, but the serpentine mineral chrysotile—accounting for 95 percent of all asbestos used in the past and 99 percent of current production—is not. For example, one case study involved a school that was located next to a 150,000-ton rock containing chrysotile. Thousands of children played on the rocks over a one-hundred-year period, but not a single case of asbestos-related disease developed in any of the children. The difference seems to be in how the human body responds to amphibole compared to chrysotile. The immune system can eliminate chrysotile fibers much more readily than amphibole, and there is also evidence that chrysotile in the lungs dissolves and is excreted. This remains a controversial area, and the US government still treats all forms of asbestos the same. This is not true of some European governments.
The risk of developing any type of disease from exposure to normal levels of asbestos fibers in outdoor air or the air in closed buildings was thought to be extremely low. The calculations of Melvin Benarde in Asbestos: The Hazardous Fiber (1990) show that the risk of dying from nonoccupational exposure to asbestos is one-third the risk of being killed by lightning. The Health Effects Institute made similar calculations in 1991 and found that the risk of dying from asbestos is less than 1 percent the risk of dying from exposure to secondary tobacco smoke. However, the risk of developing a disease from normal or low levels of asbestos may be more dangerous than originally thought. It was found that individuals who were involved in the rescue, recovery, and cleanup of the World Trade Center in New York City after the September 11, 2001, terrorist attacks were at a high risk of developing an asbestos-related disease because asbestos was used in the construction of the North Tower of the World Trade Center. After the building was attacked, hundreds of tons of asbestos were released into the air. While it was clear to researchers that heavy and lengthy exposure to asbestos increases individuals' chances of developing mesothelioma and asbestosis, investigators found asbestos-related diseases in individuals who had only a brief exposure. Furthermore, some evidence exists that the family members of those who worked at the World Trade Center after the attacks had an increased risk of developing mesothelioma.
Bibliography
"Asbestos Exposure and Cancer Risk." National Cancer Institute, 21 Nov. 2021, www.cancer.gov/about-cancer/causes-prevention/risk/substances/asbestos/asbestos-fact-sheet. Accessed 15 July 2024.
Bartrip, Peter. Beyond the Factory Gates: Asbestos and Health in Twentieth Century America. New York: Continuum, 2006.
Carroll, Stephen, et al. Asbestos Litigation. Santa Monica, Calif.: RAND, 2005.
Castleman, Barry. Asbestos: Medical and Legal Aspects. 5th ed. New York: Aspen, 2005.
Chatterjee, Kaulir Kisor. “Asbestos.” In Uses of Industrial Minerals, Rocks, and Freshwater. New York: Nova Science, 2009.
Craighead, John E., and Allen R. Gibbs, ed. Asbestos and Its Diseases. New York: Oxford University Press, 2008.
Deffeyes, Kenneth S. “Asbestos.” In Nanoscale: Visualizing an Invisible World. Illustrations by Stephen E. Deffeyes. Cambridge, Mass.: MIT Press, 2009.
Dodson, Ronald, and Samuel Hammar, eds. Asbestos: Assessment, Epidemiology, and Health Effects. Boca Raton, Fla.: CRC Press, 2005.
"EPA Actions to Protect the Public from Exposure to Asbestos." US Environmental Protection Agency (EPA), 18 Mar. 2024, www.epa.gov/asbestos/epa-actions-protect-public-exposure-asbestos. Accessed 15 July 2024.
McCulloch, Jock, and Geoffrey Tweedale. Defending the Indefensible: The Global Asbestos Industry and Its Fight for Survival. New York: Oxford University Press, 2008.
Maines, Rachel. Asbestos and Fire: Technological Trade-Offs and the Body at Risk. New Brunswick, N.J.: Rutgers University Press, 2005.