Malignant mesothelioma is caused by asbestos exposure. There is a latency period of 20 to 50 years or more between initial exposure and development of the disease with the average being between 35 and 40 years. Rare instances have been documented when the interval was less than 20 years.
The incidence of mesothelioma rises with the intensity and duration of exposure to asbestos. However, there are numerous cases of mesothelioma among people with very little occupational exposure or even household exposure. There are cases of people getting mesothelioma 30 or 40 years after a summer job working construction, and cases of housewives or children being exposed from work clothing. Many people being diagnosed with mesothelioma now were exposed in the Navy many years ago, often unknowingly. Many school buildings were also built with asbestos.
Despite what many believe, asbestos is not banned in the United States. Some countries have moved to ban asbestos but even if it is banned from new product sales, asbestos remains a problem because the material is around in so many buildings. The World Health Organization estimates that worldwide, 125 million people are exposed to asbestos on their jobs every year, and 90,000 die from asbestos diseases.
Characteristics of Asbestos Fibers and Their Potential for Risk
The different physical characteristics of various asbestos fibers play a role in their ability to pose an increased or decreased risk for disease. Some fibers are more easily inhaled and become lodged in tissue making them difficult for the body to remove. This is known as biopersistence.
Fiber size and composition influences the biopersistence of asbestos fibers. Chrysotile has an increased degree of solubility that decreases its biopersistency as compared to amphiboles that are more biopersistent and have a greater tendency to cause asbestos disease.
Fiber diameter and length plays a role in determining whether or not a fiber poses a risk. Fibers that are smaller than 0.50 μm in diameter or greater than 10 μm in length are considered more hazardous since these fibers are more likely to remain in the body thus giving them time to have a negative impact on one’s system.
The following are some conclusions that have been drawn from research in regards to asbestos fibers and their respiratory effects:
1) fibers that are long and thin tend to become lodged in the lungs more easily
2) curly fibers (chrysotile) tend to be less likely to become lodged in the lungs than straight fibers (amphibole)
3) fibers that get lodged in the lungs are normally thinner than 0.7 μm and almost always thinner than 1 μm
Risk of Asbestos Fibers as it Relates to Ambient Exposure
Research has shown that there is a correlation between inhalation of asbestos fibers in occupational environments that require exposure to the hazardous particles and development of asbestosis, mesothelioma, and lung cancer. There has been limited evidence when it comes to proving that these diseases develop from ambient exposure to asbestos fibers.
Some of the difficulty may stem from the complexity of various factors involved such as defining the level of exposure, the duration of exposure, long latency periods from initial exposure through disease onset, age when exposure took place, fiber types and sizes, lifestyle behaviors that may contribute to the problem, and exposure to other hazardous particles.
Materials Containing Asbestos
Most insulation materials before the mid-1970s contained asbestos. Many other construction materials also contained asbestos. Some of the most common products were:
- Insulation on pipes
- Boiler insulation
- Insulating cements, plasters, and joint compounds that came in powder form and created a lot of dust before being completely mixed with water.
- Fireproofing spray
- Firebrick and gunnite used for internal insulation of furnaces, boilers, and other vessels
- Roof, floor, and ceiling tiles.
- Transite siding
- Brakes and clutches
The following tradesmen could have worked around asbestos:
- Insulators (also known as asbestos workers) who actually installed insulation
- Boilermakers who constructed boilers which were often several stories high and filled with insulation
- Plumbers, pipefitters, and steamfitters who fitted and welded pipes together and often worked in small unventilated compartments in ships where large quantities of insulation were used
- Plasterers who worked with fireproofing spray on steel beams
- Shipyard workers and Navy personnel
- Electricians, mechanics
- Bricklayers; millwrights; carpenters; and other building trades workers
- Steel workers; refinery and other industrial workers;
- Maintenance workers; laborers; many others.
Industrial sites typically had the heaviest exposure. These include shipyards where ships were constructed or overhauled, power plants, refineries, paper mills, manufacturing plants, foundries, and construction sites.
For more details, see , Asbestos Exposure at Work.
Sources for information on this page:
Agency for Toxic Substances and Disease Registry: Tox FAQs for Asbestos
Environmental Protection Agency: Asbestos and Indoor Air
Minnesota Dept of Health – Asbestos Health Effects
Naval Facilities Engineering Command – About Asbestos