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How risky is asbestos?

How Risky Is Asbestos? The Energy and Environmental Policy Center of Harvard University's John F. Kennedy School of Government held a three-day symposium on the "Health Aspects of Asbestos in Buildings" on December 14-16, 1988. The purpose of the symposium was to assess the health risk that buildings with asbestos containing materials (ACM) present to occupants, facility maintenance personnel, and workers engaged in asbestos removal activities.

Internationally recognized experts addressed a series of questions, including: What is the extent of the health risk posed by asbestos in buildings? Who in the population is being exposed? How do we measure the level of exposure, and how do we communicate the extent of the associated risk?

New interpretations of published findings on exposures in buildings and of occupational cohort studies were presented at the Harvard symposium. The toxicity of fiber type as well as factors influencing the response of individuals exposed to those fibers was discussed. Mesothelioma and lung cancer risks were projected through extrapolations from epidemiologic studies of workplace environments. The principal findings from the symposium are summarized below.

1 Asbestos is not a single mineral. It is a term used to refer to a number of fibrous inorganic minerals that share specific properties. The most common of these is chrysotile--representing over 95 percent of all asbestos used in buildings. The second major group is amphiboles--including amosite and crocidolite.

The differences in fiber type and dimension can be of significance in determining health risks. For example, the amphibole fibers pose a much greater risk of mesothelioma than the chrysotile fibers. Respirable fibers longer than -5 microns are thought to be of much greater risk than short fibers. Measurements made by the EPA indicate that exposures to fibers 5 microns and longer inside buildings are much lower than average airborne concentrations of fibers.

2 Occupant risk should be determined by exposures to airborne fibers. At the present time there is no single optimum method to characterize potential exposure to airborne fibers from asbestos-containing materials in buildings. However, the consensus view was that air sampling, using the direct-preparation TEM methodology, is the methodology of choice for current exposure assessment.

The available asbestos air monitoring database for buildings in the U.S. indicates extremely low average concentrations of airborne asbestos under normal building use conditions.

3 The extent of risks associated with exposures to asbestos in contaminated buildingds differs for various groups who reside or work in these buildings. Custodial, maintenance, and construction workers may be exposed to elevated levels of asbestos for brief periods of time. In contrast, however, most office workers, teachers, students, and other building occupants typically do not come in close contact with asbestos-containing materials.

4 There are considerable differences in the value of many of the earlier studies on asbestos health effects. A major, nearly universal, deficiency was the differences in measurement techniques. Uncertainties relating to the amount of asbestos fibers in the workplace environment also affected the value of study conclusions.

For example, a main data source, paraticle concentration measurements (pre-1960), did not count fibers separately, let alone differentiate them by size, length, or type. Consequently, most studies used to quantify risk were unable to quantify differences in response associated with fiber type and size. In some studies, impurities or the presence of other substances may have affected the risk estimates.

5 Process factors and environmental effects have potentially significant impact upon risk. Occupational cohort studies show that relative risk of lung cancer from exposures to amosite or mixed (amphibole and chrysotile) fibers is typically higher than risk associated with processes in which chrysotile is bonded with other materials, as in the production of cement or friction products. However, studies of lung cancer among chrysotile textile workers show increases in relative risk higher than those encountered using mixed fiber types (insulation material or cement products).

6 Mesothelioma has been modeled as a risk independent of age. Risk increases in proportion to the product of exposure and as a power of time (typically around ). For calculating mesothelioma risk, fiber type is believed to be essential.

The majority of asbestos-related mesotheliomas can be attributed to amphiboles (primarily crocidolite), a much less commonly used variety of asbestos in the U.S. The mesothelioma risk from exposure to chrysotile asbestos, the type of asbestos most commonly found in U.S. schools and buildings, is believed to be considerably lower. Present U.S. regulation does not consider variations in the biological potency of different fiber categories.

7 Lung cancer and mesothelioma risk models have been developed for asbestos exposure that are considered to be conservative (i.e., tend to overpredict rather than underpredict the risks). Recent data indicate that the average concentration of asbestos in schools and other buildings that have asbestos-containing materials is generally well below the 0.001 (mixed) fibers/ml used in risk calculations performed for school children.

Using these conservative risk models and exposures higher than typically measured, the projected lifetime risk from exposure to mixed asbestos fibers is one death among a cohort of 100,000 children. (1) These risk projections do not differ greatly among investigators.

8 The risk of 1 in 100,000 is far less than most other commonly experienced environmental health risks, such as those attributable to environmental tobacco smoke and radon. Even though the risk posed by in-place asbestos is very small, both in absolute and relative terms, the public perception of these risks is high, which often leads to the decision to simply remove all of the asbestos-containing materials.

9 Removal itself is not without risk. Removal and disposal operations expose a large fraction of removers to high concentrations of airborne asbestos and also may potentially increase rather than decrease indoor asbestos concentrations and associated health risks. Thus, there exists a question whether removing asbestos-containing materials now, as opposed to at the time of demolition, will reduce or increase health risks.

10 In many cases, spending money on asbestos removal will likely decrease funding which might be available to support other public and educational measureS, which could be far more effective in reducing environmental health risks.

11 For buildings with asbestos-containing materials, air sampling and risk calculations should be performed as a component of selection of the most effective management strategy from the point of view of health protection and net risk reduction.

This evaluation should include the risks to all groups: occupants of these buildings, custodial and maintenance personnel, and workers involved in the removal of the asbestos. The potential for exposure to asbestos fibers is much greater for the last two groups than for the first. Therefore, personnel monitoring studies should be initiated to evaluate worker exposure and worker protection procedures under various conditions of asbestos management.


(1) Assuming 10-year exposure to the mixed asbestos fibers from building insulation material at concentrations of 0.001 (regulatory) fibers/ml, where regulatory fibers are defined to be at least 5 microns in length, with a length-to-diameter ratio of 3 to 1 greater.
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Author:McCarthy, John F.; Spengler, John D.; Ozkaynak, Haluk; Lee, Henry
Publication:Journal of Property Management
Date:Mar 1, 1990
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