Health Effects of Asbestos Exposure
Non-Occupational Exposure
In 1980, a National Institute of Occupational Safety and Health (NIOSH)/OSHA work group concluded that there was no level of exposure to asbestos below which clinical effects did not occur. They recommended a Permissible Exposure Limit (PEL) based on the lowest measurable airborne fiber level, 0.01 f/cc. EPA has accepted this conclusion and recommends that 0.01 fibers per cubic centimeter be used to define the successful completion of asbestos abatement work. The risks associated with low levels of cumulative exposure are not well-established, and considerable debate surrounds the issue.
There are many factors which complicate studies of non-occupational exposure, including a lack of data on incidental exposures which may occur, lack of data on non-occupational levels (f/cc) of exposure, and the lack of a control group (zero, or at least known "near zero" exposure). Confounding variables such as migration into and from communities and multiple exposures to other toxic chemicals and carcinogens consistently frustrate attempts to generalize about the risk of low level exposure.
At low levels of exposure, for example, asbestos may serve only as a "cancer promoter", acting as a co-factor along with other substances and carcinogens to elevate the risk of developing cancer above normal. This is clearly the case with asbestos and cigarette smoke, but other chemicals and agents may react in a similar way to the presence of asbestos fibers.
Because asbestos fibers do accumulate in the lungs, and because the risk of developing disease does increase as the cumulative dose increases, exposure to asbestos should be controlled or eliminated whenever possible. Even a relatively minor source of airborne asbestos fibers should be abated, avoided, or minimized in order to maintain the cumulative dose at a minimum.
In order to prevent outbreaks of asbestos disease in the future, asbestos exposure must be controlled today. When asbestos materials are managed calmly and deliberately and handled properly when removed (or abated) the potential for non-occupational exposure can be significantly reduced.
Ambient Exposure
Detectable levels of asbestos fibers in the ambient air are a fact of life. Studies have reported typical levels of 0.005 f/cc in urban or metropolitan areas. HMA's own testing and air level measurements have supported these studies. For the major urban areas here in the San Francisco Bay Area, such as San Francisco and Oakland, levels of 0.004 f/cc to 0.005 f/cc are common. Suburban areas are typically lower, usually in the 0.003 f/cc to 0.004 f/cc range. A few years ago, HMA had occasion to conduct air testing 13 miles out in the Pacific Ocean off the California coast, and found levels of 0.002 f/cc (TEM), lower than urban areas but not zero.
Principal sources of ambient asbestos are typically listed in the text books as "quarrying,mining and milling, and manufacturing". Here in the USA, most (but not all) manufacturing of asbestos-containing products has ceased. For example, many automobile and truck brake shoes and clutch linings were manufactured with asbestos, and many such vehicles are on the roadways today. Friction applied during braking (and clutch use) releases fibers.
Many buildings were constructed with Asbestos Containing Materials. The present OSHA standards reflect that buildings constructed prior to January 1, 1981 are presumed to be constructed with asbestos-containing building materials (PACM). Again, proper maintenance and management of the asbestos containing materials can significantly reduce potentials for exposures.