Asbestos is the name given to a number of naturally occurring fibrous silicate minerals that have been mined for their useful properties such as thermal insulation, chemical and thermal stability, and high tensile strength. Asbestos fibers have been used in a broad variety of industrial applications. In the peak period of asbestos consumption in industrialized countries, some 3,000 applications, or types of products, have been listed. Because of recent restrictions and changes in end use-markets, most of these applications have been abandoned and the remainder is pursued under strictly regulated conditions.
Hazards associated with asbestos
The relationship between workplace exposure to airborne asbestos fibers and respiratory diseases is one of the most widely studied subjects of modern epidemiology. Asbestos-related health concerns were first raised at the beginning of the century in the United Kingdom, which appears to have been the first country to regulate the asbestos-user industry. It wasn’t until the early 1960s, however, that, researchers firmly established a correlation between worker excess exposure to asbestos fibers and respiratory cancer diseases. This finding triggered a significant research effort to unravel important issues such as the influence of fiber size, shape, crystal structure, and chemical composition; the relationship between exposure levels and diseases; the consequence of exposure to asbestos fibers in different types of industries, or from different types of products; and the development of technologies to reduce worker exposure.
The research efforts resulted in a consensus in some areas, although controversy still remains in other areas. It is widely recognized that the inhalation of long (considered usually as longer than 5μm), thin, and durable fibers in high concentrations over a long period of time can induce or promote lung cancer. It is also widely accepted that asbestos fibers can be associated with three types of diseases: asbestosis: a lung fibrosis resulting from long-term, high level exposures to airborne fibers; lung cancer: usually resulting from long-term high level exposures and often correlated with asbestosis; mesothelioma: a rare form of cancer of the lining (mesothelium) of the thoracic and abdominal cavities.
A further consensus developed within the scientific community regarding the relative carcinogenicity of the different types of asbestos fibers. There is strong evidence that the genotoxic and carcinogenic potentials of asbestos fibers are not identical; in particular, mesothelial cancer is most strongly associated with amphibole fibers.
- No studies are available on the acute (short-term) effects of asbestos in animals or humans.
- Lung effects are a major health concern from asbestos, as chronic (long-term) exposure to asbestos in humans via inhalation can result in a lung disease termed asbestosis. Asbestosis is characterized by shortness of breath and cough and may lead to severe impairment of respiratory function and ultimately death.
- Other effects from chronic inhalation exposure to asbestos include an accumulation of scar-like tissue in the membranes that surround the lung, pulmonary hypertension, and immunological effects.
- The U.S. Environmental Protection Agency (EPA) has not established a Reference Concentration (RfC) or a Reference Dose (RfD) for asbestos.
- No studies are available on the reproductive or developmental effects of asbestos via inhalation, and oral studies in animals have not reported any reproductive or developmental effects.
- Cancer is a major concern from asbestos exposure, as inhalation exposure can cause lung cancer and mesothelioma (a rare cancer of the thin membranes lining the abdominal cavity and surrounding internal organs), and possibly gastrointestinal cancers in humans. Oral exposure to asbestos may be associated with cancer of the esophagus, stomach, and intestines. However, the evidence on cancer from oral asbestos exposure is not conclusive. EPA has classified asbestos as a Group A, human carcinogen, based primarily on inhalation studies, and has calculated an inhalation unit risk estimate of 2.3 × 10-1 (fibers/mL)-1.
- Airborne exposure to asbestos may occur through the erosion of natural deposits in asbestos-bearing rocks, from a variety of asbestos-related industries, or from clutches and brakes on cars and trucks. The concentrations in outdoor air are highly variable.
- Asbestos has been detected in indoor air, where it is released from a variety of building materials such as insulation and ceiling and floor tiles. Typical concentrations in indoor range from 1 to 200 ng/m3.
- Asbestos may be released to water from a number of sources, including erosion of natural deposits, corrosion from asbestos-cement pipes, and disintegration of asbestos roofing materials with subsequent transport into sewers.
Assessing Personal Exposure
- It is possible to test for the presence of asbestos fibers in urine, feces, or mucus. In addition, a chest X-ray, although it cannot detect the asbestos fibers themselves, can detect early signs of lung disease caused by asbestos.
Health Hazard Information
- No studies were located on the acute (short-term) toxicity of asbestos in animals or humans.
Chronic Effects (Noncancer):
- Chronic (long-term) inhalation exposure to asbestos in humans can lead to a lung disease termed asbestosis, which is a diffuse fibrous scarring of the lungs. Symptoms of asbestosis include shortness of breath, difficulty in breathing, and coughing. Asbestosis is a progressive disease, i.e., the severity of symptoms tends to increase with time, even after the exposure has stopped. In severe cases, this disease can lead to death, due to impairment of respiratory function.
- Other effects from asbestos exposure via inhalation in humans include pulmonary hypertension and immunological effects.
- Feeding studies in animals exposed to high doses of asbestos have not detected any evidence of adverse toxic effects.
- The U.S. Environmental Protection Agency (EPA) has not established a Reference Concentration (RfC) or Reference Dose (RfD) for asbestos.
- No studies were located on the developmental or reproductive effects of asbestos in animals or humans via inhalation.
- Birth defects were not noted in the offspring of animals exposed to asbestos in the diet during pregnancy.
- No effects on fertility were observed in animals exposed to asbestos in the diet during breeding, pregnancy, and lactation.
- A large number of occupational studies have reported that exposure to asbestos via inhalation can cause lung cancer and mesothelioma (a rare cancer of the membranes lining the abdominal cavity and surrounding internal organs).
- Individuals who smoke and are also exposed to asbestos have a greater than additive increased risk of developing lung cancer.
- Several occupational studies have reported an increase in gastrointestinal cancer from inhalation exposure to asbestos and subsequent oral ingestion.
- Long- and intermediate-range asbestos fibers (>5μm) appear to be more carcinogenic than short fibers (<5μm).
- Several epidemiological studies have found an association between asbestos in drinking water and cancer of the esophagus, stomach, and intestines; however, confounding factors and the short follow up time relative to the long latent period for tumor formation make it difficult to interpret the results.
- A series of large-scale lifetime feeding studies in animals reported that intermediate-range asbestos fibers increased the incidence of a benign tumor of the large intestine in male rats, while short-range asbestos fibers showed no significant increase in tumor incidence.
- EPA considers asbestos to be a human carcinogen (cancer-causing agent) and has ranked it in EPA's Group A.
- EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated an inhalation unit risk estimate of 2.3 × 10-1 (fibers/mL)-1. EPA estimates that, if an individual were to breathe air containing asbestos at 0.000004 fibers/mL(2) over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of breathing air containing this chemical. Similarly, EPA estimates that breathing air containing 0.00004 fibers/mL would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 0.0004 fibers/mL would result in not greater than a one-in-ten-thousand increased chance of developing cancer.
Asbestosis and asbestos pleural disease
Asbestosis and asbestos pleural diseases are lung diseases first found in naval shipyard workers. Asbestosis and asbestos pleural disease are nonmalignant asbestos diseases that are slowly progressive and are the result of cumulative exposure to asbestos. They can be severely disabling and potentially fatal. These asbestos diseases cause impairment of pulmonary function, including small airway obstruction, a reduction in lung capacity, breathing restriction, and a reduction in the ability to transfer oxygen from air into the blood. Approximately one in seven people who suffer from asbestosis eventually develop asbestos lung cancer
Asbestosis is a scarring of lung tissue caused by the inhalation of asbestos fibers. A portion of the fibers reach the alveoli (air sacs) where oxygen is transferred into the blood. Asbestos activates the lung’s immune system and starts a reaction best described as an inflammatory process. Scavenger white blood cells (macrophages) try to break down the asbestos (phagocytosis) but are not successful, causing other cells (fibroblasts) to grow and form connective–tissue–based scars.
The formation of scar tissue or collagen in the lungs is known as fibrosis. The scar tissue slowly builds up, often reducing the lung’s ability to deliver oxygen to the blood and remove carbon dioxide (reduced diffusion capacity). The total lung capacity or TLC may also be reduced. In severe cases, the impairment of lung function can strain the heart, or even result in heart disease, such as right–sided heart failure or “cor pulmonale.”
The inflammatory process starts within hours or days after inhalation of asbestos and injury at the cellular level begins shortly thereafter. In people who develop asbestosis, the inflammatory process continues to progress, fueled by indestructible asbestos fibers, even after exposure to asbestos ceases.
This asbestosis inflammatory process may continue undetected for decades causing no pain or respiratory symptoms. In many people, the process eventually produces symptoms—breathing abnormalities and radiographic changes. Usually, the first symptoms are shortness of breath and a dry cough. These symptoms often precede abnormalities on chest x–ray or pulmonary function tests. The period between exposure and diagnosis is called “latency” and may range from 10 to 50 years.
'Asbestos pleural disease is a nonmalignant disease caused by inhalation of asbestos fibers that scar the pleura. The pleura is the thin membrane lining the lung and chest cavity. If the scarring is diffuse and extends along the chest wall, it is called pleural thickening. If the scarring is more focused and well–defined, it is called pleural plaques.
Asbestos pleural disease results in a similar scarring process as the one that occurs inside the lung with asbestosis; however, it occurs in the lining of the lungs rather than in the lungs. Pleural thickening and pleural plaques can cause shortness of breath and impair lung function. Although its symptoms may be treated, asbestos pleural disease is permanent and progressive with no cure. Even after exposure to asbestos has ceased, scarring continues due to the body’s interaction with retained asbestos fibers.
Pleural scarring, which is often seen in conjunction with asbestosis, can be detected on chest x–rays and CT scans and usually reflects a significant history of exposure to asbestos. It normally takes at least 10 years after the first exposure to asbestos for asbestos pleural disease to develop.
Malignant mesothelioma is a rare form of cancer caused by exposure to asbestos. The name is often shortened to “mesothelioma.” This form of cancer is peculiar because the only known cause is from asbestos exposure. The disease attacks the mesothelial cells, which are specialized cells that make up the membranes lining the chest and abdominal cavity. Mesothelium, or the tissue formed by mesothelial cells, helps protect the organs by producing a lubricating fluid that allows the organs to move without irritating nerves.
Malignant mesothelioma frequently involves severe respiratory problems. The virus SV40 may also be a factor in the disease in some people. Mesothelioma is not lung cancer, even though it can affect the the lungs. Cigarette–smoking does not cause mesothelioma, although smoking can lead to lung cancer and effect the chances of contracting other asbestos–related diseases such as asbestosis.
Common locations where malignant mesothelioma occurs in asbestos–exposed workers are the pleural and peritoneal regions. Pleural mesothelioma is cancer of the pleura, which is the membrane that lines the lungs and the chest cavity. Peritoneal mesothelioma is cancer of the peritoneum, which is the lining of the abdomen. Both involve serosal membranes (delicate membranes composed of connective tissue).
Symptoms of pleural mesothelioma may not become apparent until many years after the first exposure to asbestos. Pleural mesothelioma patients usually experience general difficulty in breathing (dyspnea), pain in the chest, or both. Other signs of the disease may include hoarseness, difficulty swallowing (dysphagia), or coughing up of blood (hemoptysis). Over half of patients with pleural mesothelioma have pain in the lower back or at the side of the chest. An increase in waist size or abdominal pain may be a symptom of the growth of cancer cells in the abdomen and peritoneal mesothelioma. The physician will use imaging techniques and take fluid or tissue samples to make a mesothelioma diagnosis.
Patients in the early stages of asbestos lung cancer often do not have symptoms. Some early symptoms, present in only about 15% of lung cancer cases, are a persistent cough, chest pain, hoarseness, weight loss, and bloody or rust–colored sputum (spit or phlegm). However, these symptoms could also indicate other diseases. The effects of lung cancer are often greatly increased by cigarette smoking (by about 50%). Cancer of the gastrointestinal tract can also be caused by asbestos. The latency period for cancer is often 15-30 years. Despite the common misconception, asbestos does not cause head-aches, sore muscles or other immediate symptoms. As mentioned above, the effects often go unnoticed for 15-40 years.
- Asbestos is the name applied to a group of six different minerals that occur naturally in the environment.
- The most common mineral type is white, but others may be blue, gray, or brown.
- These minerals are made up of long, thin fibers that are somewhat similar to fiberglass.
- Asbestos is neither volatile nor soluble; however, small fibers may occur in suspension in both air and water.
- The main uses of asbestos are in building materials, paper products, asbestos-cement products, friction products, textiles, packings and gaskets, and asbestos-reinforced plastics.
- Asbestos use in the United States is currently decreasing.
Health Data from Inhalation Exposure
| Concentration in fibers/m3
|| Health numbersa
|| Regulatory, advisory numbersb
|10.0||• EPA Cancer Risk Level c
(1-in-a-million excess lifetime risk) = 4 fibers/mL
|• ACGIH TLV
(2 fibers >5μm/cm3)
(chrysotile and other forms of asbestos)
|0.1||• ACGIH TLV
(0.5 fibers >5μm/cm3)
• OSHA PEL
(0.2 fibers >5μm/cm3)
• NIOSH REL and ACGIH TLV (crocidolite)
(0.1 fiber <5μm/cm3)
|a Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.
b Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers are nonregulatory values provided by the Government or other groups as advice.
ACGIH TLV--American Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effects.
NIOSH REL--National Institute of Occupational Safety and Health's recommended exposure limit; NIOSH--recommended exposure limit for an 8- or 10-h time-weighted-average exposure and/or ceiling.
OSHA PEL--Occupational Safety and Health Administration's permissible exposure limit expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effect averaged over a normal 8-h workday or a 40-h workweek.
- Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Asbestos (Draft). U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 1989.
- E.J. Calabrese and E.M. Kenyon. Air Toxics and Risk Assessment. Lewis Publishers, Chelsea, MI. 1991.
- U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
- U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
- U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Asbestos. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.
- Also for more information see asbestos.com
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Environmental Protection Agency, Agency for Toxic Substances and Disease Registry, and USGS. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Environmental Protection Agency, Agency for Toxic Substances and Disease Registry, and USGS should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.