In the past, asbestos exposure was associated mainly with mining and milling of the raw material and with workers engaged in construction and product manufacture or use of end products. In the industrialized west, these heavy asbestos exposures peaked during the 1960s and 1970s and then it declined as worker protection regulations were put in place and later as industrial use of asbestos decreased. Because of long latency periods (10–40 years), workers exposed to asbestos in the 1960s and 1970s are now manifesting asbestos-associated diseases. Indeed, the incidence of asbestos-associated diseases among people occupationally exposed is beginning to peak and will likely begin to decline some time in the next 2 decades. National statistics that illustrate this trend are available at

http://www.cdc.gov/niosh/topics/surveillance/ords/NationalStatistics.html

Today in the United States, most occupational exposures occur during repair, renovation, removal, or maintenance of asbestos that was installed years ago. People can also be exposed at home, both to old sources of asbestos as a result of activities such as home renovation or to new sources of asbestos as a result of certain types of recreational activities and hobbies such as auto repairs or gardening, which may disturb natural outcroppings of asbestos in the environment.

In the past, many occupations entailed exposures to asbestos (see table below). Studies have documented the scale of the problem.

• In the United States, an estimated 27 million workers were exposed to aerosolized asbestos fibers between 1940 and 1979 (Nicholson et al. 1982).

Secondary exposure occurred when people who did not work directly with asbestos were nevertheless exposed to fibers as a result of sharing workspace where others handled asbestos. For example, electricians who worked in shipyards were exposed because asbestos was being used to coat the ships' pipes and hulls (Pan et al. 2005).

In the past, because of a lack of proper industrial hygiene, asbestos workers went home covered in asbestos dust. The workers' families and other household contacts were then exposed via inhalation of asbestos dust

• from workers' skin, hair, and clothing, and
• during laundering of contaminated work clothes.

A mortality study of 878 household contacts of asbestos workers revealed that 4 out of 115 total deaths were from pleural mesothelioma and that the rate of deaths from all types of cancer was doubled (Joubert et al. 1991)

In addition, asbestos was released into the air and soil around facilities such as refineries, power plants, factories handling asbestos, shipyards, steel mills, vermiculite mines, and building demolitions. People living around these facilities were also exposed to asbestos.

Currently, the people most heavily exposed to asbestos in the United States are those in construction trades. This population includes an estimated 1.3 million construction workers as well as workers in building and equipment maintenance (American Thoracic Society 2004. Because most asbestos was used in construction, and two-thirds of asbestos produced is still used in this trade, risk to these workers can be considerable if the hazard is not recognized and OSHA standards are not enforced.

As noted previously, some home attic insulation and many other home and building materials produced before 1975 contain asbestos. People who live in homes with these materials are at risk of exposure if the materials are loose, crumbling, or disturbed by household activities or renovations. In such cases, the asbestos materials should be removed or encapsulated by a trained and certified asbestos contractor. For information on where to find certified asbestos contractors in your state, contact your local health department.

On the other hand, asbestos contained in intact solid material poses a negligible risk of exposure. A 1992 study of indoor air in homes and schools with asbestos-containing materials found an average concentration of 0.0001 fibers/cc (Lee et al. 1992).

There are many ways that people can also be exposed to asbestos through hobbies and recreational activities that entail contact with materials containing asbestos; some examples are such activities as home renovation, auto repair, and urban spelunking. In places where naturally occurring asbestos is close to the earth's surface, activities such as gardening and dirt biking can cause exposures if asbestos-bearing rock is disturbed.

Measurable asbestos levels in schools are usually 100 to 1,000 times below OSHA's permissible exposure limit of 0.1 fibers/cc of air for asbestos (Holland and Smith 2003). However, ATSDR does not use occupational standards when considering the risks to health of the general population from asbestos in the general environment. A specific environmental health risk assessment process is used.

Over time, public concern led to widespread removal and abatement programs. Some facilities have higher levels of airborne asbestos after removal than before, highlighting the importance of proper encapsulation or removal by trained and certified contractors.

No known truly unexposed group exists in the world. The cumulative risk of background exposures is probably minor, however, and these concentrations cannot be reduced (Hillerdal 1999). Any source of pollution that releases significant amounts of asbestos fibers should be eliminated, using proper equipment and techniques, as soon as it is discovered.

Most vermiculite used today contains low or non-detectable levels of asbestos. However, the vermiculite mined in Libby, Montana, from the turn of the 20th century to 1990 was contaminated with various fibrous amphiboles, including tremolite asbestos, and constituted 95% of the vermiculite used in the United States during that time. The vermiculite operations in Libby, Montana, are a good example of the many ways people can be at risk of asbestos exposure. In this example, mining of the asbestos- contaminated vermiculite ore in Libby resulted in asbestos exposures to

• miners
• household contacts of miners and other Libby asbestos workers
• children playing in piles of vermiculite in the area
• residents of nearby towns (where the air was contaminated by industrial activities involving asbestos)
• workers who handled the vermiculite in vermiculite exfoliation and handling sites throughout the United States after it was shipped there from Libby
• people who live in homes with vermiculite home insulation

This vermiculite was also used in potting soil, but EPA concluded that consumers “face only a minimal health risk from occasionally using vermiculite products at home or in their gardens” (EPA 2000).

For more information about amphibole-contaminated vermiculite, see

• an ATSDR map of 28 priority vermiculite exfoliating sites at http://www.atsdr.cdc.gov/asbestos/sites/national_map/.
• an EPA fact sheet about how to recognize and avoid exposure to vermiculite insulation in homes at http://www.epa.gov/asbestos/pubs/insulation.html.
• an EPA fact sheet about how to avoid asbestos exposures while using potting soils at http://www.epa.gov/asbestos/pubs/vermfacts.pdf [PDF - 21 KB].

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