Introduction

Asbestos was widely used in the United States until health concerns led to some uses being banned and some voluntary phase outs [Seidman and Selikoff 1990]. Since the early 1970s, use of asbestos has declined substantially; mining of asbestos ceased in the United States in 2002, though some asbestos continues to be imported [NIOSH 2011a].

Asbestos is still used in some construction materials. Some previously marketed asbestos-containing products, such as amphibole-contaminated vermiculite insulation, remain in many homes and other buildings in the United States. Asbestos fibers are released into the air when friable asbestos-containing materials are disturbed. In addition to being at risk for potential exposure from degradation of asbestos-containing commercial products, people in some areas of the world may be at risk because of geological deposits of asbestos at or near the earth's surface, which can release asbestos by natural weathering or man-made disturbance. Such deposits are often referred to as "naturally occurring asbestos."

For more information on the subject of naturally occurring asbestos and maps showing the locations of naturally occurring asbestos:

ATSDR website - https://www.atsdr.cdc.gov/PHS/PHS.asp?id=28&tid=4

United States Geological Services website - https://www2.usgs.gov/envirohealth/geohealth/images/GreaterThanBenchmarksMap.png

Current Commercial Uses

Today, asbestos used in the United States is imported. Recent uses of asbestos in the Unites States include

• Automobile clutches,
• Brake pads,
• Corrugated sheeting,
• Imported cement pipe,
• Roofing materials, and
• Vinyl tile [American Thoracic Society 2004].

Former Commercial Uses

Until the 1970s, asbestos was widely used in the construction, shipbuilding, and automotive industries, among others. For example, asbestos was formerly used in some of the following items:

• Boilers and heating vessels,
• Cement pipe,
• Clutch, brake, and transmission components,
• Conduits for electrical wire,
• Corrosive chemical containers,
• Electric motor components,
• Heat-protective pads,
• Laboratory furniture,
• Paper products,
• Pipe covering,
• Roofing products,
• Sealants and coatings,
• Insulation products, and
• Textiles (including curtains).

These materials remain in many buildings, ships, and automobiles built before 1975 [Seidman and Selikoff 1990 ].

Contaminated Commercial Products

Asbestos has been a contaminant in other products such as

Vermiculite contaminated with asbestos was produced as late as 1990 from a mine near Libby, Montana. The mined vermiculite ore contained amphibole asbestos. It was processed at 245 sites around the country, and contaminated vermiculite products were distributed nationally [ATSDR 2001a]. See below for a map with a sample of 30 out of the 245 sites where Libby vermiculite was processed nationwide.

Although all vermiculite currently used in potting soil is essentially amphibole-free, pre-1990 products from the Libby mine contain amphibole asbestos. Many homes still have this vermiculite insulation in their attics.

For more information on amphibole asbestos and vermiculite insulation, please refer to the ATSDR website on asbestos at http://www.atsdr.cdc.gov/asbestos/sites/libby_montana

Homes and Buildings

Besides homes that contain vermiculite insulation, asbestos in friable (easily pulverized or crumbled) construction materials is also a concern. Asbestos embedded in solid materials (such as wallboards) is less easily disturbed and therefore less likely to be released into the air unless it is cut, drilled, or sanded.

Many construction materials produced before 1975 contained asbestos including (but not limited to)

These sources of asbestos can be disturbed during home redecoration, renovation, and demolition. Asbestos can also be released during destruction of housing stock during natural or technological (human-made) disasters.

The Natural Environment

As a result of human use, asbestos fibers are now widely dispersed in the environment. Background levels in the air are extremely low, about 0.0001 fibers/cc [Holland and Smith 2003].

Asbestos is also present in the environment naturally, primarily in underground rock.

• In most areas asbestos fibers are not released into the air because the rock is too deep to be disturbed easily.
• In some areas, such as parts of California, Virginia, and New Jersey (and across the globe in Turkey and Corsica) where asbestos-bearing rock is close enough to the surface that construction and other human activities can disturb it, high concentrations of asbestos fibers can be released into the air [ATSDR 2001a; Constantolopoulos 2008; Hasanoglu et al. 2003; Luo et al. 2003].

There can be clusters of cases of a rare asbestos-related cancer, mesothelioma in places where high exposures to naturally occurring asbestos occurs.

• A recent ecological study found an elevated risk for mesothelioma occurrence in an area in New Caledonia where roads are covered in local rock that contains asbestos [Baumann et al. 2011].
• Another ecological study in California found a relationship between proximity to geologic sources of naturally occurring asbestos and incidence of malignant mesothelioma [Pan X et al. 2005].

Progress Check