Perelman School of Medicine at the University of Pennsylvania


What is Asbestos?

Asbestos is a naturally occurring mineral found in rock and soil. Asbestos minerals are divided into two major classes based on their types of fibers, serpentine (curly) and amphibole (needle-like). Chrysotile is the only member of serpentine class and is the most widely used for commercial applications in the world. It is also more flexible than the other classes of fibers called amphibole which include the other naturally occurring fibrous minerals:  crocidolite, amosite, anthophyllite, tremolite, and actinolite. Amosite is the most common in this class and are often referred to as “brown asbestos”.

Asbestos has been mined and used commercially in North America since the late 1800s and was used primarily due to its extremely durable nature and resistance to fire. These properties of asbestos were the reasons that supported its use for many years in a number of different commercial and industrial capacities. The strength of asbestos, combined with its resistance to heat, allowed it to become the material of choice in a variety of products, including, but not limited to, roofing shingles, floor tiles, ceiling materials, cement compounds, textile products, and automotive parts. Asbestos is now strictly regulated as exposure to this toxic mineral is directly and scientifically linked to a number of lung and respiratory conditions including mesothelioma.

“Regulated” Asbestos

The regulation requirements for asbestos were enacted to protect public health and welfare.  Under the Clean Air Act (CAA), Congress gave the Environmental Protection Agency (EPA) the responsibility for enforcing regulations relating to asbestos renovations and demolition activities. The EPA is also allowed to delegate responsibility to state or local agencies but retains the authority to oversee agency performance to enhance and enforce the regulations as necessary.

Asbestos containing material (ACM) which is any material containing more than 1% of asbestos by weight is regulated by the EPA in the following areas: schools, public and commercial buildings including those that are to be demolished or renovated. Asbestos in the workplace is regulated by The Occupational Safety and Health Administration (OSHA).

Fibers with demonstrated carcinogenic effect

Asbestos has been designated as a known human carcinogen. All types of asbestos are carcinogenic however, the amphibole type appears more potent in causing mesothelioma than the serpentine (chrysotile) type although both types cause lung cancer and mesothelioma. When asbestos containing products are disturbed through various activities, they release microscopic fibers that become airborne. If inhaled, these fibers can become trapped and accumulates in the lungs over time causing inflammation, scarring, and other health effects including the development of cancer.

The risk of cancer after asbestos exposure depends on a number of factors, the most important of which are:

  • level (how much) and the duration (length) of exposure
  • time since exposure occurred
  • age at which exposure occurred
  • smoking history of the exposed person. Cigarette smoking and asbestos exposure increase the risk of getting lung cancer. In contrast, the effect of asbestos on mesothelioma risk does not appear to be increased by smoking.
  • type and size of the asbestos fibers- Amphibole asbestos fibers are retained in the lung longer than chrysotile asbestos fibers. In fact, several studies suggest that amphibole asbestos types (tremolite, amosite, and especially crocidolite) may be more harmful than chrysotile, particularly for mesothelioma

The average time from exposure to cancer development (latency period) is 20 to 30 years for lung cancer although, there are studies which show that workers with 1 to 12 months of exposure had an increased risk in developing lung cancer a number of years later. Lung cancer has also been reported in household contacts and family members of asbestos workers presumably from exposure to asbestos carried home on work clothes.

Mesothelioma, an aggressive and usually fatal cancer is relatively rare in the general population, but is often observed in asbestos workers and sometimes in family/household members. Studies have found strong associations between exposure to asbestos fibers and the development of mesothelioma. For mesothelioma, the latency is generally 30-40 years, with the longer periods seen where there had been lower levels of asbestos exposure. Similar to lung cancer, several studies have indicated that the risk of mesothelioma after asbestos exposure depends on the time since exposure (latency), with the risk increasing exponentially with time after about 10 years. Early studies indicated that diagnosis with mesothelioma was fatal within a short period of time (often within months), however other studies indicate that survival time after diagnosis may be influenced by exposure intensity (amount). Some scientists believe that early identification and intervention of mesothelioma may increase survival