Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. The prolonged inhalation of asbestos fibers can cause serious illnesses including malignant lung cancer, mesothelioma, and asbestosis (a type of pneumoconiosis). The European Union has banned all use of asbestos and extraction, manufacture and processing of asbestos products.
Asbestos became increasingly popular among manufacturers and builders in the late 19th century because of its sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. It was used in such applications as electrical insulation for hotplate wiring and in building insulation. When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement (resulting in fiber cement) or woven into fabric or mats.
Asbestos mining began more than 4,000 years ago, but did not start large-scale until the end of the 19th century. For a long time, the world’s largest asbestos mine was the Jeffrey mine in the town of Asbestos, Quebec.
Health Problems
All types of asbestos fibers are known to cause serious health hazards in humans. While it is agreed that amosite and crocidolite are the most hazardous asbestos fiber types, chrysotile asbestos has produced tumors in animals and is a recognized cause of asbestosis and malignant mesothelioma in humans.
Mesotheliomas have been observed in people who were occupationally exposed to chrysotile, family members of the occupationally exposed, and residents who lived close to asbestos factories and mines. According to the NCI, “A history of asbestos exposure at work is reported in about 70 percent to 80 percent of all cases. However, mesothelioma has been reported in some individuals without any known exposure to asbestos.” The most common diseases associated with chronic exposure to asbestos include: asbestosis and pleural abnormalities (mesothelioma, lung cancer). Asbestosis has been reported primarily in asbestos workers, and appears to require long-term exposure, high concentration for the development of the clinical disease. There is also a long latency period (incubation period of an infectious disease, before symptoms appear) of about 12 to 20 years.
Studies have shown an increased risk of lung cancer among smokers who are exposed to asbestos compared to nonsmokers.
Asbestos exposure becomes a health concern when high concentrations of asbestos fibers are inhaled over a long time period. People who become ill from inhaling asbestos are often those who are exposed on a day-to-day basis in a job where they worked directly with the material. As a person’s exposure to fibers increases, because of being exposed to higher concentrations of fibers and/or by being exposed for a longer time, then that person’s risk of disease also increases. Disease is very unlikely to result from a single, high-level exposure, or from a short period of exposure to lower levels.
Identification and Assessment
A fiber cannot be identified or ruled out as asbestos, either using the naked eye or by simply looking at a fiber under a regular microscope. The most common methods of identifying asbestos fibers are by using polarized light microscopy (PLM) or transmission electron microscopy (TEM). PLM is less expensive, but TEM is more precise and can be used at lower concentrations of asbestos.
If asbestos abatement is performed, completion of the abatement is verified using visual confirmation and may also involve air sampling. Air samples are typically analyzed using phase contrast microscopy (PCM). PCM involves counting fibers on a filter using a microscope. Airborne occupational exposure limits for asbestos are based on using the PCM method.
The American Conference of Governmental Industrial Hygienists has a recommended Threshold Limit Value (TLV) for asbestos of 0.1 fibers/mL over an 8 hour shift. OSHA in the United States and occupational health and safety regulatory jurisdictions in Canada use 0.1 fibers/mL over an 8 hour shift as their exposure limits.
Common Building Materials Containing Asbestos
Most products manufactured today do not contain asbestos. In the industrialized world, asbestos was phased out of building products mostly in the 1970s with most of the remainder phased out by the 1980s. Asbestos containing building materials in residences includes a variety of products, such as: stiple used in textured walls and ceilings; drywall joint filler compound; asbestos contaminated vermiculite, vinyl floor tile; vinyl sheet flooring; window putty; mastic; cement board; furnace tape; and stucco. Other sources of asbestos containing materials include fireproofing and acoustic materials.
Exposure
Asbestos exposure becomes an issue if asbestos containing materials become airborne, such as due to deterioration or damage. Building occupants may be exposed to asbestos, but those most at risk are persons who purposely disturb materials, such as maintenance/construction workers. Housekeeping/custodial employees may be at increased risk as they may potentially clean up damaged or deteriorated asbestos containing materials without knowing that the material contains asbestos. Asbestos abatement/remediation workers and emergency personnel such as firefighters may also become exposed.
Environmental asbestos
Asbestos can be found naturally in the air outdoors and in some drinkable water, including water from natural sources. Studies have shown that members of the general (non-occupationally exposed) population have 10,000-999,999 asbestos fibers in each gram of dry lung tissue, which translates into millions of fibers and tens of thousands of asbestos bodies in every person’s lungs.
Asbestos from natural geologic deposits is known as “naturally occurring asbestos” (NOA). Health risks associated with exposure to NOA are not yet fully understood, and current US federal regulations do not address exposure from NOA. Many populated areas are in proximity to shallow, natural deposits which occur in 50 of 58 California counties and in 19 other U.S. states. In one study, data was collected from 3,000 mesothelioma patients in California and 890 men with prostate cancer, a malignancy not known to be related to asbestos. The study found a correlation between the incidence of mesotheliomas and the distance a patient lived from known deposits of rock likely to include asbestos; the correlation was not present when the incidence of prostate cancer was compared with the same distances. According to the study, risk of mesothelioma declined by 6% for every 10 km that an individual had lived away from a likely asbestos source.
Portions of El Dorado County, California are known to contain natural amphibole asbestos formations at the surface. The USGS studied amphiboles in rock and soil in the area in response to an EPA sampling study and subsequent criticism of the EPA study. The EPA study was refuted by its own peer reviewers and never completed or published. The study found that many amphibole particles in the area meet the counting rule criteria used by the EPA for chemical and morphological limits, but do not meet morphological requirements for commercial-grade-asbestos. The executive summary pointed out that even particles that do not meet requirements for commercial-grade-asbestos may be a health threat and suggested a collaborative research effort to assess health risks associated with “Naturally Occurring Asbestos.”
However, the main criticism pointed at EPA was that their testing was conducted in small isolated areas of El Dorado where there were no amphibole asbestos deposits, thus the language regarding amphibole, nonfibrous “particles”. Actual surface amphibole deposits in residential areas were ignored for testing purposes. Thus no final findings were published by ATSDR since the criticism was correct and the effort of combined EPA/ATSDR teams were wasted time and money.
Great deals of Fairfax County, Virginia were also found to be underlain with tremolite. The county monitored air quality at construction sites, controlled soil taken from affected areas, and required freshly developed sites to lay 6 inches (150 mm) of clean, stable material over the ground.
Globally, collected samples from Antarctic ice indicate chrysotile asbestos has been a ubiquitous contaminant of the environment for at least 10,000 years. Snow samples in Japan have shown ambient background levels are one to two orders of magnitude higher in urban than in rural areas. Higher concentrations of airborne asbestos fibers are reported in urban areas where there is more ACM (asbestos containing materials) and mechanisms of release (vehicles braking and weathering of asbestos cement materials); concentrations in the range of 1–20 ng/m^3 have been reported. Fibers longer than 5μm are rarely found in rural areas. Ambient concentrations using TEM analysis have been based on mass measurements.