New Mexico Mineral Symposium — Abstracts

In accordance with U.S. Environmental Protection Agency (USEPA) publication no. 20T-2003 (1990), the term "asbestos" describes six naturally occurring fibrous minerals. Of these six, chrysotile is the fibrous (asbestiform) variety of the mineral serpentine, and the other five are fibrous (asbestiform) varieties of amphibole. Although chrysotile and its mas¬sive counterpart, serpentine, as well as members of the amphibole group are common in many geologic terranes, there are only a few localities worldwide where these asbestiform minerals are in sufficient concentration and of the required quality (that is, of highly fibrous habit) to be mined profitably.

The major asbestos-producing countries, in decreasing order of estimated production tonnage (as available in the literature, from many sources, for the years 1978-1981 and tabulated by Schreier, 1989), are as follows: USSR, Canada, Zimbabwe, Brazil, Italy, USA, Greece, Australia, western Germany, and small additional production from a few other countries. In most cases, except South Africa and Finland, the production is of "white asbestos," chrysotile. South Africa is the only current source of "blue asbestos" (asbestiform blue amphibole, crocidolite) and of "brown asbestos" (asbestiform brown amphibole, amosite). Western Australia, in the Wittenoom area of the Hamersley Range, was a major producer of "blue asbestos" until 1966 when all mining there was terminated (Trendall and Blockley, 1970). Approximately 95% or more of the world's production of asbestos is chrysotile from a relatively small number of commercial sources (Harben and Bates, 1984; Ross, 1981; Schreier, 1989). Noncommercial occurrences (in association with serpentinites) of chrysotile are estimated to be much more common, worldwide, than the well-known commercial deposits.

Most of the major commercial chrysotile deposits (mines) occur in the northern hemisphere; most serpentine occurrences plotted by Schreier (1989) are also in the northern hemisphere. (One exception is the relatively small Precambrian occurrence of anthophyllite asbestos, a fibrous variety of amphibole, in eastern Finland where production stopped in 1975; Ross, 1981.) In contrast, the largest asbestos producers in the southern hemisphere are those of two types of amphibole, crocidolite ("blue asbestos") and amosite ("brown asbestos"); both types are mined in the Transvaal Province of South Africa and large reserves of "blue asbestos" are still available in the Hamersley Range of Western Australia. Less chrysotile production in the southern hemisphere is from South Africa, Zimbabwe, Australia, and Brazil. Amphibole asbestos production and occurrence in the southern hemisphere is intimately tied to the vast Precambrian iron deposits, both in South Africa, and Western Australia.

Of the six asbestos types, only four have been used significantly in commercial applications. By 1980 90% of all asbestos mined worldwide was of the chrysotile ("white asbestos") variety (Ross, 1981), with the main suppliers being mines in the Thetford Mines area of the eastern townships of Quebec, Canada, and in the central and southern Urals of the USSR. Two to three percent of the world's asbestos production has been the crocidolite ("blue asbestos") variety, mainly from South Africa and Western Australia. Amosite ("brown asbestos") also accounts for only about 2-3% of all asbestos ever produced (Ross, 1981).

Although federal policy in the United States does not differentiate between different types of asbestos (Mossman et al., 1990), medical studies on the pathogenicity of the different forms of asbestos (Mossman et al., 1990; see also Ross, 1984, for an extensive review) show that "blue asbestos" (crocidolite) poses much greater health hazards (in occupational settings) than chrysotile. Occupational exposure to asbestos can cause the following types of disorders: asbestosis, lung cancer, mesotheliomas (cancer of the pleural and peritoneal membranes), and benign changes in the pleura (Mossman et al., 1989). Crocidolite ("blue asbestos") fibers appear to be most pathogenic, especially with respect to mesothelioma. Smoking is a strong contributor to incidence of the above diseases, especially lung cancer (Ross, 1984).

Although asbestos has caused disease in the work place (see Ross, 1984 for review), three questions need to be answered: 1) What is the main asbestos type in US buildings? 2) Does airborne asbestos dust present in schools and other buildings present a risk to the occupants? and 3) What does the natural ambient air (from outside the building) contribute to the fiber count inside a building? The answer to question #1, is simple: the asbestos fiber found in buildings is mainly chrysotile. The answer to question #2 is also simple: available data do not support the concept that low-level (nonoccupational) exposure to asbestos is a health hazard in buildings and schools (Mossman et al., 1990). The study of nonoccupation¬al exposure of women (nonminers) to chrysotile fibers in the mining towns of the Thetford Mines region, Quebec (where these women lived for much of their lives in very heavy, nonoccupational exposure to chrysotile dust emitted from the mining operations and the waste dumps; Pampalon, 1979; report updated by Siemiatycki, 1982; see also Ross, 1984) and other Canadian health studies show that there is no excess mortality in these regions (in a nonoccupational setting) and that the air and water, both of which contain significant amounts of chrysotile fiber, are safe to breathe and drink. The answer to question #3 is more difficult, and the conclusions less well established. Normal geologic weathering processes of amphibole- and chrysotile-rich rocks worldwide contribute a natural background (of fiber content) to the atmosphere and hydrosphere. (In this regard, it must be noted that fiber counts of air and water samples include, as recommended by the U.S. Occupational Safety and Health Administration (OSHA), all naturally occurring acicular minerals with a length¬to-width ratio of 3 for fibers having a length greater than 5 Am.) Studies of Antarctic ice cores (dated as older than 10,000 years; Kohyama, 1989) show fiber concentrations (ex¬pressed as fibers per liter of water) that are very similar to values commonly measured in modern waters that are generally unaffected by man-made fiber pollution. Careful studies of fiber count and fiber type in essentially nonpolluted air are very few, but Kohyama (1989) shows a geometric mean of 9.7 fibers/liter of air over the Pacific Ocean and some isolated, mainly volcanic islands about 600 mi to the southeast of Japan. Almost all of this fiber is chrysotile. This fiber count per liter may well represent a global and natural fiber back¬ground of something like 10 fibers/liter. The answer to question #3, therefore, is that there is a background contribution (resulting from natural erosional processes) to the global air mass. This was clearly stated by Abelson (1990): "We live on a planet on which there is an abundance of serpentine- and amphibole-containing rocks. Natural processes have been releasing fibers throughout Earth history. We breathe about 1 million fibers per year."

Misunderstanding and fear of asbestos and also mandates by the Environmental Protection Agency (EPA) have generated an explosive growth of asbestos identification and removal companies, working mainly in public schools, other public buildings, and hospitals. Extension of such EPA requirements to all public and commercial buildings containing asbestos will cost approximately $100-150 billion (Mossman et al., 1990). For example, New York City has 800,000 public and private buildings, of which 544,000 are estimated to contain significant amounts of asbestos (comment by A. F. Appleton, Environmental Protection Commissioner; NY Times, July 15, 1990). In this regard, an EPA report of 1990 "Managing Asbestos in Place," lists four pertinent "facts:" Fact 1: "Although asbestos is hazardous, the risk of asbestos-related disease depends upon exposure to airborne asbestos fibers" (note the continued lack of distinction of asbestos types); Fact 2: "Based upon available data, the average asbestos levels in buildings seem to be very low. Accordingly the health risk to most building occupants appears to be very low." Fact 3: "Removal is often not a building owner's best course of action to reduce asbestos exposure. In fact, an improper removal can create a dangerous situation where none previously existed." Fact 4: "EPA only requires asbestos removal to prevent significant public exposure to airborne asbestos fibers during building demolition or renovation activities." Unfortunately, because of asbestos fear and misinformation, asbestos removal (instead of encapsulating the wall or ceiling materials in place) is becoming a bigger and costlier business, not smaller. Buildings with known asbestos (even if material is found to be in sound condition), which are up for sale, lose much of their value because of the fear not only of the asbestos in them, but of future and open-ended litigation about the presence of asbestos.

Why the fear and panic? Statements such as "one fiber can kill you" are very effective, although completely untrue. Humankind is not being killed, nor has it been killed, by the globally known natural levels of fiber in the atmosphere. This must mean that there must be some threshold level (of fibers/liter) in the atmosphere below which there is no likelihood of disease. This is quite contrary to the linear dose models that lead to the statement ("one fiber theory") that one fiber of inhaled asbestos will cause cancer. Such statements are unsupported by available data.

Two important questions remain with regard to a fiber background level in the global atmosphere. Kohyama (1989) notes that 99% of all the fibers in sixteen air samples (taken over the Pacific Ocean and isolated, small volcanic islands off Japan) consist of chrysotile.
1) Why such a preponderance of chrysotile? It is very likely that the Coalinga chrysotile area in the San Benito Mountains of California is a unique natural supply source of micron-sized chrysotile fibers for the global atmosphere as well as local water runoff. The chryso¬tile is the result of extensive chemical alteration and structural deformation of serpentine rock over an area of approximately 50 mil (about 32,000 acres). Chrysotile asbestos fibers from this very large area of rock and soil exposures rich in chrysotile (range 1-10 Am) can travel many thousands of miles in the global atmosphere, and 1-i.cm particles carried to the top of a cloud could stay airborne for months if the particles were not cleansed out of the atmosphere by precipitation (R. C. Schell, pers. comm.). And 2) is there direct evidence for the presence of global-airborne amphibole fibers that have resulted from normal weathering processes? The most relevant study is by Paoletti et al. (1987), in which the mineral-particle content was determined by transmission electron microscope (TEM) techniques of lung tissues of ten residents who died in the Rome, Italy area of causes not related to occupational exposure to dust. In six of the ten cases amphibole was noted in the lung burden, and chrysotile was noted in only one. The amphiboles are considered to reflect part of the mineral component (in the atmosphere) that is the result of normal weathering processes.
 

References:

1. Abelson, P. H., 1990. The asbestos removal fiasco (Editorial): Science, v. 247, p. 1017.
2. Harben, P. W., and Bates, R. L., 1984, Geology of the nonmetallics: Metal Bulletin Inc., New York, 392 pp. Kohyama, N., 1989, Airborne asbestos levels in nonoccupational environments in Japan; in Bignon, J., Peto, J., and Saracci, R. (eds.), Nonoccupational exposure to fibers: World Health Organization, International Agency for Research on Cancer, pp. 262-276.
3. Mossman, B. T., Bignon, J., Corn, M., Seaton, A., Gee, J. B. L., 1990, Asbestos: scientific developments and implications for public policy: Science, v. 247, pp. 294-301.
4. Mossman, B. T., and Gee, J. B. L., 1989, Asbestos-related diseases: New England Journal of Medicine, v. 320, pp. 1721-1729.
5. New York Times, 1990, Cost of anti-asbestos plans raises debate in New York: July 15, p. 14. Pampalon, R., 1979, A comparative analysis of mortality in asbestos-mining and other towns of Quebec: Unpublished work document (Document no. 5596/79c): Asbestos-Health Project, Division of Epidemiological Studies, Ministry of Social Affairs, Quebec, Canada, 21 pp.
6. Paoletti, L., Batisti, D., Caiazza, S., Petrelli, M. G., Taggi, F., DeZorzi, L., Dina, M. A., and Donelli, G., 1987, Mineral particles in the lungs of subjects resident in the Rome area, and not occupationally exposed to mineral dust: Environmental Research, v. 44, pp. 18-28.
7. Ross, M., 1981, The geologic occurrences and health hazards of amphibole and serpentine asbestos: Mineral??ogical Society of America, Reviews in Mineralogy, v. 9A, pp. 279-323.
8. Ross, M., 1984, A survey of asbestos-related disease in trades and mining occupations and in factory and mining communities as a means of predicting health risks of nonoccupational exposure of fibrous minerals; in Benjamin Levadie (ed.), Definitions of asbestos and other health-related silicates: American Society for Testing and Materials, STP 834, pp. 51-104.
9. Schreier, H., 1989, Asbestos in the natural environment: Studies in Environmental Science 37, Elsevier, New York, 159 pp.
10. Siemiatycki, J., 1982, Health effects on the general population (mortality in the general population of asbestos mining areas): World Symposium on Asbestos, Montreal, Quebec, Canada, proceedings, pp. 337-348. Trendall, A. F., and Blockley, J. G., 1970, The iron formations of the Precambrian Hamersley Group with special reference to associated crocidolite: Geological Survey of Western Australia, Bulletin 119, 366 PP.
11. USEPA, 1990, Managing asbestos in place: a building owners' guide to operations and maintenance program for asbestos-containing materials: U.S. Environmental Protection Agency, Washington, 20T-2003, 40 pp.