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Figure 5. SEM photomicrographs of crocidolite and riebeckite at three magnifications: Crocidolite (left) at A. X 500; B, X 2,500; and C, X 10,000. Riebeckite (right) at D, X 500; E, X 2,500; and ~, X 10,000. Rectangles indicate the area shown at the next higher magnifications. 211

Riebeckite and crocidolite particles are compared at higher magnifications in figure 5. The outlined areas in the scanning electron micrographs indicate the area displayed at the next higher magnification. Again, note the presence of a few elongated cleavage fragments of riebeckite visible at the higher magnification. In contrast, the aspect ratio of the crocidolite will decrease with decreasing particle size because the individual fibers cannot cleave further along the fiber axis; they can only break into shorter segments. Aspect Ratio Existing regulatory standards are based on counting specific mineral particulates with aspect ratios of 3 to I or greater. The aspect ratio has little mineralogical significance for individual particulates but is applicable statistically to a large number of particles. A few relatively long thin particles are produced as cleavage fragments from the crushing and grinding of many nonasbestiform minerals. Conversely, similar milling treatment will result in a few short segments of true fibers from the asbestiform varieties. However, statistically, the length-to-width characteristics of the milled amphiboles and serpentine and their asbestiform varieties are significantly distinct, as shown by the data in figures 6 to 9. 1:1 3:1 MILLED AN71iOPHYWTE -Anthophyllite --MthophyHRe aabeetae 5:1 10:1 20:1 50:1 ASPECT RATIO 100:1 200:1 500:1 .a.M a Yr M N1Y O Figure 6. Frequency polygons for the aspect ratios of anthophyllite and anthophyllite asbestos. N O a7 1.+ 212 O $ v

C3 70 f 60 50 E 40 r ~ 30 ~ 20 10 MILLED TREMOLITE -Tremoiite --Tremolite asbestos Figure 7. Frequency polygons for the aspect ratios of tremolite and tremolite asbestos. 1:1 3:1 5:1 10:1 ~ 20:1 50:1 100:1 200:1 ASPECT RATIO a..w c. u~. H ie.w. v MILLED HORNBLENDE Figure 8. Frequency polygons for the aspect ratio of hornblende. 5:1 10:1 20:1 50:1 100:1 ASPECT RATIO x .ac. o 213

CHRYSOTILE Commercial milled chrysotile ,_A~ / ~ --Ambient air sample 1:1 3:1 6:1 10:1 20:1 50:1 ASPECT RATIO 100:1 200:1 500:1 1000:1 «Me.u er ..w. N10Wp Figure 9. Frequency polygons for the aspect ratios of commercial-grade chrysotile and chrysotile in ambient air. Figures 6, 7, and 8 show the frequency polygons of the aspect ratio distribution for milled samples of the normal nonasbestiform variety of three amphiboles--anthophyllite, tremolite, and hornblende, respectively. Note that in all three examples, approximately 70 percent of the particles have an aspect ratio of less than 3 to 1, and 95 percent of the particles have a length-to-width ratio of less than 10 to 1. The frequency distri- bution maxima of the aspect ratios for milled anthophyllite asbestos and tremolite asbestos are significantly higher than those for the normal, nonasbestiform variety. Thirty to forty percent of the asbestiform particulates are in the 10-to-l-or-langer class, with a significant number of particles having an aspect ratio greater than 20 to 1. Figure 9 shows the distribution frequencies for a milled commercial grade of chrysotile asbestos and for chrysotile particulates collected on ambient air filters in the vicinity of a serpentine rock quarry. For the commercial-grade chrysotile, over 50 percent of the particles have an aspect ratio greater than 50 to 1, whereas the frequency distribution for the ambient air sample has a maximum between 10 to I and 20 to 1. These results are anticipated because the higher aspect ratios for the commercial-grade chrysotile are characteristic of the significantly longer starting material. All of the aforementioned samples except the ambient air were milled, then dispersed in water for collection on a suitable substrate. The samples were then measured using electron microscopy at magnifications of 5,000 to 10,000. The ambient air sample, collected near a serpentine rock quarry, was measured using a TEM with magnifications of X 5,000 to X 32,000. Based on these data, one test for distinguishing the presence or absence of the asbestiform variety of a mineral could be an examination of the frequency distribution of the aspect ratio for that mineral. Assuming positive Identification of the mineral type, then the designation of variety would be based both on particle morphology and the frequency maximum of the aspect ratio. Cleavage fragments will generally have a frequency maximum less than 3 to 1, whereas the asbestiform varieties will fall between 10 to 1 and 20 to 1 or higher, depending on the characteristics of the mineral and the history of the sample, particularly the type and degree of milling. If a sha e or size limits are pl aced on characterizing mineral articulates, such limits shobe based on medicai evidence or on some limitation of the charing techm Que ang -sostated. 214

1C 3 Particulates From Unknown Sources Samples such as environmental airborne or waterborne mineral particulates collected at a considerable distance from a possible source are examples of particulates from an unknown source. The samples could have been collected at a location so distant from a known source that other mineral particulates originating from other sources compose most of the sample. The source of the particulates in an environmental sample may be located by taking additional samples at selected intervals in the direction of, and closer to, the suspected source. However, several factors must be considered: The direction of air and water currents with respect to the suspected source, and the proximity to and direction of other sources with regard to the suspected source. One study found very low concentration of airborne chrysotile upwind from a source compared with a concentration two orders of magnitude greater downwind [11]. Another important consideration is the level of natural or human disturbances of particulates; for example, strong versus weak winds, or heavy versus light vehicle traffic. In some instances, it may be possible to identify the source if the mineral particulates of interest have unique trace elements or combinations of elements that are specific to the probable mining or milling operation emitting the particulates. Detailed elemental analysis using the X-ray spectral capabilities of an SEM or TEM is required on both the suspected source and the particulates. Applications The following examples illustrate the application of mineral terminology and identification-characterization procedures to three types of problems: (1) chrysotile determination in ambient-air samples collected near a serpentine rock quarry, (2) iden- tification of asbestiform minerals in ceilings and walls of public buildings,'sand (3) characterization of a mineral product. These examples illustrate, in order, the *need for higher magnification than available with the light optical microscope, the use of~ various characterization techniques to screen and identify asbestiform minerals, and the 'fudgment of the analyst in distinguishing cleavage fragments and asbestiform particles. Ambient-Air Samples Collected Near Serpentine Rock Quarry The Bureau of Mines is working with State and Federal officials to measure mineral particulates in ambient-air samples collected in the vicinity of a serpentine rock quarry. Optical microscopic procedures at about X 500 are limited to the identification of mineral particulates longer than 5 pm with an aspect ratio of 3 to 1 or larger (criteria set by the Mining Enforcement and Safety Administration and the Occupational Safety and Health Administration). The mineralogist can further identify the particles as belonging to the serpentine, amphibole, or other mineral group with index oils (Table 2). The serpentine rock in the quarry is interlaced with small veins of chrysotile (figure 10). Optical microscopic procedures used for industrial hygiene are adequate for the detection of large chrysotile fiber bundles. These fiber bundles of commercial-grade chrysotile can be several micrometers or larger in diameter. In contrast, the mining and crushing operations in the quarry plus transport of particulates over a distance breaks bundles of fibers down to fibers or fibrils with diameters of 250 to 1,000A (Table 3). 215

Figure 10. Macrophotograph showing chrysotile veins in serpentine rock (X 1). Figure 11 is a series of SEM photomicrographs of a mixture of chrysotile and non- asbestiform serpentine handpicked from a small vein in the serpentine rock quarry. Note that at X 450 (corresponding to the optical microscope magnification), only one or two bundles of chrysotile are faintly visible; the predominant particles are the nonasbestiform serpentine. As the magnification is increased, the high concentration of chrysotile fibers becomes readily visible. The fiber diameter size data in Table 3 indicate that more than 95 percent of the chrysotile fibers in these ambient-air samples are below the limit of resolution of the optical microscope. Although many other scientists have pointed out the limitation of the o tical ~rocedures for chr s~otile in ambi~'ent a)r, there is neetc for cont~em ~has that higher magnifc-ation techniques are necessary for env7ronmental and reg~u ato~ry samples. 216

vl-f , . T~.,--; ---,~-~ r . . U . ..i f +F~" .~ I ~ ~ 0~ +! .. , .. r~ ;• ~ :~ 'A ~ ~ Figure 11. Mixture of nonasbestiform serpentine and chrysotile at five magnifications: A. X 450; 8, X 2,250; C, X 1,800; D, X 9,000; and E, X 18,000. Rectangles indicate t~ie area shown in the next panel. 217

Asbestos in Ceiling and Wall Materials A possible environmental hazard is the release of asbestos from ceilings and walls in homes, churches, schools, and various other public and commercial buildings. Because of the very high number of potential samples to be examined by various State or Federal agencies, a rapid and reliable screening procedure is necessary to identify those samples that warrant further test. Three complementary analytical methods for screening, identifi- cation, and semi-quantitative estimate of the asbestiform mineral concentration are x-ray diffractometry, differential thermal analysis, and microscopy (light optical and scanning electron). The screening Identification procedures can be relatively simple because chrysotile is the principal asbestos mineral used for building insulation materials, with amosite used to a much lesser extent. In 18 samples from a midwestern municipal health department, chrysotile was a major constituent (>50 weight-percent) in 2 samples, a minor constituent Cl to 10 weight-percent) in 12 samples, and not detected in 4 samples. Other minerals present in various concentrations in these samples were calcite, quartz, gypsum, and mica. Amosite was found as a major constituent in the ceiling of an older building located on a university campus. The presence of either serpentine or amphibole minerals in the insulation materials can be used as a probable indication of asbestos. Therefore, screening tests are based on the presence or absence of characteristic differential thermal analysis or x-ray diffraction peaks of either serpentine or amphibole minerals. For the positive samples, confirmation of the presence of the asbestiform variet reguires some type of microscopic examination because the thermall~ and x-ray '~rifd f action methods do not identify the mineral variety. Some samples will be composed of a mixture of synthetic and natural fibers, such as the mixture of fiberglass and chrysotile shown in figure 12. Generally, it is not difficult to identify the synthetic fibers based on their larger diameter and the more ~'niform appearance. Figure 12. Sample from university building, showing a mixture of chrysotile and fiberglass (X 140). Amphiboles and Talc Asbestos-related health regulations are having a significant impact on the domestic talc industry from occupational exposure at the mines and mills and at various manufacturing plants that use talcs in their operations. Certification that the talc does or does not contain asbestiform minerals is important because the occupational health 218

(03 requirements are much more restrictive if the talc is designated as containing asbestiform serpentine or amphibole minerals. Talc is both the name of a specific mineral, Mg3Si*01o(OH)2, and a commercial term for a mixture of minerals ranging from essentially 100 percent talc to blends where the mineral talc is a minor constituent [12,13]. Semi-quantitative estimation of the serpentine and/or amphibole mineral concentration, if present, can be obtained by x-ray diffraction and differential thermal analysis. Several talc deposits contain a variable amount of tremolite. Therefore, the essential question faced by the analyst is whether or not the tremolite is fibrous. Judgment required of the analyst is illustrated by the sample shown in figure 13. This sample consists of platy talc, cleav- age fragments of an amphibole, and minor to trace amounts of fibrous amphibole. For this latter sample, the 3-to-1 aspect-ratio criteria would greatly overestimate the number of fibrous amphibole particles collected on air filters or other monitors. Figure 13. Platy talc, tremolite cleavage fragments, and a fibrous tremolite particle (A) (X 400). References [1] Journal of the American Industrial Hygiene Association. Recommended Procedures for Sampling and Counting Asbestos Fibers. Vol. 36, pp. 83-90 (February 1973). [2] Berger, H., Asbestos Fundamentals. (Chemical Publishing Co., New York) 171 pp. (1963). [3] Beaman, 0. R. and File, D. M. , Quantitative Determination of Asbestos Fiber Concentrations. Anal. Chem. , 48, pp. 101-110 (January 1976). [4] Langer, A. M., Approaches and Constraints to Identification and Quantification of Asbestos Fibers. Environmental Health Perspectives, 9, pp. 133-136 (1974). [5] Cressey, B. A. and Zussman, J. , Electron Microscopic Studies of Serpentinites. Canadian Mineralogist, 14, pp. 307-313 (1976). [6] Mumpton, F. A. and Thompson, C. S., Mineralogy and Origin of the Coalinga Asbestos Deposit. Clays and Clay Minerals, 23, pp. 131-143 (1975). [7] Ernst, W. G., Earth Materials (Prentice-Hall, Inc., New York, 1969). 219

[8] Deer, W. A., Howie, H. A., and Zussman, J., Rock Forming Minerals. (John Wiley & Sons, Inc., New York, 1963) 5 v. [9] Wylie, A., Optical Properties of Asbestiform Amphiboles and Their Nonasbestiform Analogs. Available from A. Wylie, Bureau of Mines, College Park, Maryland 20740. [10] Ruud, C. 0. , Barrett, C. S., Rissell, P. A., and Clark, R. L., Selected Area Electron Diffraction and Energy Dispersive X-Ray Analyses for the Identification of Asbestos Fibres, a Comparison, Micron, 7, pp. 115-132 (1976). [11] John, W., Berner, A., Smith, G., and Wesolowski, J. J., Experimental Determination of the Number and Size of Asbestos Fibers in Ambient Air. Calif. State Department of Health, Rept. AIHL/SP-1, 36 pp. (January 1976). [12] Hamer, D. H., Rolle, F. R., and Schelz, J. P., Characterization of Talc and Associated Minerals. J. American Industrial Hvgiene Association, 37, pp. 296-304 (May 1976). [13] Rohi, A. N., Langer, A. M., Selikoff, I. J., Tordini, A., Klimentidis, R., Bowes, D. R., and Skinner, 0. L. , Consumer Talcums and Powders--Mineral and Chemical Characteriz- ation. J. Toxicology and Environmental Health, 2, pp. 255-284 (1976). Discussion J. LEINEWEBER: You brought up the question of cleavage fragments vs fibers, and asbestiform vs non-asbestiform varieties. I would like to ask why you attach so much significance to this. I think Dr. Kotin couched it most directly yesterday: the body doesn't have a dictionary. When we see fibers, if they are in the size range and if we accept this philosophy, does it matter where they come from? W. CAMPBELL: I think all health data has been based on commercial asbestos, correct? LEINEWEBER: Not necessarily commercial asbestos, but fibers of one type or another. CAMPBELL: OK, fibers. LEINEWEBER: Man-made mineral fibers or natural mineral fibers. CAMPBELL: There has been little medical studies made upon cleavage fragments. Now these may be just as harmful as fibers, but until you find this out you should call them by their proper names. To call a cleavage fragment a fiber does not help anybody. LEINEWEBER: I don't see any reason for muddying the waters with the semantic dif- ferences. CAMPBELL: I think there is some dispute whether or not there is a difference between a fiber, based on surface properties and a much larger length-to-width, and a cleavage fragment. Until you find this out you should call it either a fiber or a cleavage fragment. They may be equally harmful if they are both 20:1 and 0.5 pm in diameter, but this really has not been studied. The whole problem with the Lake Superior region was the debate whether or not the cummingtonite fragments were the same as the amosite asbestos. LEINEWEBER: This, in that context, was an argument based on the shenanigans that normally take place in the court of law, and here we are in a scientific environment. CAMPBELL: I am not a medical scientist. Obviously I don't know if a cleavage fragment is the same harmful particle as an asbestiform particle, but until you find this out; you just call it by the proper name. It does not help to call them both the same when they may be different. 220