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C 5 National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20, 1977. (Issued t,ovember 1978) FIBROUS AND ASBESTIFORM MINERALS James R. Kramer Department of Geology McMaster University Hamilton, Ontario LBS 4M1 Canada Abstract Asbestiform minerals may be differentiated from other elongate minerals by comparing their length and aspect ratio distributions in the greatest percentile level. Individual fiber analyses of UICC and other well-characterized samples suggest a possible 20-40 percent intensity ratio variation relative to Si of major cations. There is a very small amount of evidence to suggest that fibers other than asbestos are toxic. Key words: Acicular; asbestiform; asbestos; elemental composition; fibers. Introduction I The ability to differentiate between acicular minerals, fibrous minerals, and asbesti- form minerals is most significant to the work of analysts, health researchers, and mineralogists. Zoltai [21, p. 13-31]1 defines the terms carefully, discusses the history of the relevant terms, and shows how the discrepancies in the use of the terms found today has evolved. In short, the differentiation of the terms asbestos, asbestiform, fiber, fibrous, and acicular has been obscured in many cases and in different applications. One reason for a large part of the overlap of the usage of the terms is the difficulty in separation of one term from another on an analytical basis at the scale of the transmission electron microscope. When enumerating elongate particles at the micrometer scale, in many cases a cleavage fragment can appear similar to a fiber or an asbestiform mineral. Thus the advent of the transmission electron microscope to identify and enumerate particles on an environmental monitoring basis has brought certain ambiguities. The Glossary of Geolo [1] defines some of the pertinent terms as follows: "ASBESTOS: (a) a commercial term applied to a group of highly fibrous silicate minerals that readily separate into long, thin, strong fibers of sufficient flexibility to be woven, are heat resistant and chemically inert, and possess a high electric insulation, and therefore are suitable for uses (as in yarn, cloth, paper, paint, brake linings, tiles, insulation cement, fillers, and filters), where incombustible, nonconducting, or chemically resistant material is required. (b) a mineral of the asbestos group, principally chrysotile (best adapted for spinning) and certain fibrous varieties of amphibole (ex. tremolite, actinolite and crocidolite). (c) a term strictly applied to the fibrous variety of actinolite. syn: asbestus, amianthus, earth flax, mountain flax. ASBESTIFORM: said of a mineral that is fibrous, i.e., that is like asbestos. ACICULAR: (cryst) said of a crystal that is needlelike in form. cf. fascicular, sagenitic. 'Figures in brackets indicate the literature references at the end of this paper. 19 N O ~ w ~ 0 a m N H+

FIBROUS: said of the habit of a mineral, and of the mineral itself (e.g. asbestos), that crystallizes in elongated, needlelike grains or fibers." The more restrictive definition of asbestos (c) is not presently used. Thus asbestiform is a restricted usage of fibrous pertaining to asbestos. In the general field of mineralogy, asbestiform has not been a' commonly used term. Taken as a whole, one can easily imagine that overlap at an analytical level among the definitions of acicular, asbestiform, and fibrous definitions could occur. In a bulk sample, the distribution (bundle, fibrils, splitting), fiber length, and concentration of fibers would be used to distinguish between asbestiform and fibrous in most cases. Acicular would be distinguished from fibrous and asbestiform in that the properties of a fiber (flexibility, bundles, splitting) are not present. When minerals are dispersed, occur separately and are examined at the micrometer scale, the distinguishing characteristics for these terms disappear or are highly obscured. At this microscopic level, it is most difficult to distinguish among cleavage fragments, acicular minerals, and fibers. In no cases, however, are cleavage fragments considered to fall into the definitions of asbestiform, fibrous, or acicular. In another discussion of asbestiform [20, p. 19], it is considered "a type of mineral fibrosity in which the fibers and fibrils possess high tensile strength and flexibility." Spiel and Leineweber [18] point out that all asbestos minerals have overlapping tensile strengths; and methods of measurement are difficult "with large variations in results using the same and different techniques." Furthermore, there are virtually no tensile strength data on other fibers and cleavage fragments. Flexibility is related to the "harshness" or flexural modulus of fibers [18]. It is not clear what differences exist between asbestiform fibers and cleavage fragments of amphiboles. There is found considerable variation in the flexural modulus of chrysotile which may be due to the water content, mineral impurities, or orthorhombic and monoclinic crystal forms in the fibers. Another approach to obtain a working definition and differentiation of asbestos fibers and other elongate (length/width > 3) mineral fragments is to consider the definitions in terms of their health significance. Length and aspect ratios within certain defined limits have been proposed as the only important mineral parameters to be considered in respiratory disease. If one accepts this argument with no additional caveats, one could easily extend the length factor considerations to any elongate particle provided that the length and length/width criteria are met. This argument would then demote the analytical differentiation of the terms to a mineralogical wrangle; furthermore, there would be little necessity to distinguish among the various minerals in most cases. Following the extension of the length argument further, one then becomes faced with the conclusion that many minerals commonly occurring in rocks and soils on the earth's surface would be considered a health risk. Cralley [8] suggested that the ubiquity of occurrence of elongate mineral and non- mineral particles in autopsies may be related to the ubiquity of occurrence in the modern environment. He suggests that variable response in the lung may depend upon the chemical and physical characteristic of the fibers, but he does not state what specific characteristics should be studied. One might therefore conclude that all, or certain sizes of, elongate particles might be considered with variable response in the lung depending upon the mineralogy and surface properties. Lists of some of these common fibrous or acicular minerals are given in Kramer [12] and Zoltai [20]. There is very little epidemiological, animal, or cytotoxicity data on elongate and fibrous minerals other than asbestos. Table 1 summarizes the results obtained for studies on elongate/fibrous minerals other than asbestos from searching TOXLINE, MEDLINE, and Chemical Abstracts for the past few years. Almost all of the few elongate/fibrous minerals tested showed some toxicity, and there is some suggestion for endemic lung conditions related to soils. Many equidimensional minerals were not active or as active as the elongate/fibrous minerals in hemolytic studies. Almost all of the minerals tested were silicates, so it is not possible at present to generalize to all minerals. 20

Table 1. Toxicity of fibrous minerals other than asbestos. Mineral System and effect Reference General soils and endemic pleural plaques 13 Sepiolite-palygorskite increased enzyme activity 11 lactic acid Inhibition hemolytically active 17 endemic pleural calcifications 4 and soils tumors in rats, i.p. injection 15 Amphiboles amphibole in soil and 5 pleural plaques Arfvedsonite i.p. carcinogenicity in rats 16 Vermicullite i.p. carcinogenicity in rats 10 Apatite-nepheline dust effects 3 i.t. effect, rat lungs 9 Talc (tremotite) hemolytically active 17 Nemalite hemolytically active 17 Gypsum allergic reactions 14 chronic bronchitis 14 There is no specific information on the nature of the surfaces of the minerals, except that in one study of Schnitzer and Pundsack [17], the hand cut specimens of asbestos and other fibrous minerals were not hemolytically active. Interestingly, amphibole asbestos is not hemolytically active. However, there are very little data available to arrive at any definitive conclusions. In addition, Webster [19] has noted that in animal studies with monkeys, non-fibrous nepheline dust has produced interstitial fibrosis. This suggests that other factors besides fibrosity are responsible for the development of fibrosis. In summary, there is difficulty at the sub-micrometer level to differentiate asbesti- form, fibrous, and acicular minerals. Furthermore, there is no health evidence which might be used in an alternate classification of elongate particles. The relative response of different fibrous minerals is not clear. Since definitive animal studies and epidemiological information exist for asbestos minerals only, it is pertinent to investigate parameters which might be used to differentiate between asbestos minerals, other fibers, and cleavage fragments found in the environment. Length and aspect ratio distributions are examined for occupational asbestos samples and for environmental samples, and the composition of fibers and intra-fiber composition are examined to ascertain variations within a sample. N 21 a 0 ~ N W

Fiber Morphology The fiber length and often the fiber width are characterized in virtually all toxicity studies, and the length is often considered the most important factor in health aspects of fibers. More often than not, the mass-median length or median length is stated in reports of research. It is not uncemmon for the median length of occupational exposures to coincide with the median length of environmental measurements. Median length does not, however, provide information of the entire length distribution. Therefore, it is worthwhile to consider what variations if any exist for the entire length distribution of fibers measured in an occupational exposure and in an environmental exposure. Figure 1 summarizes length data for both chrysotile and amphibole fibers. Figure la compares the length distribution of 300 environmental samples of fibers measured in air and water environments by this laboratory to the length distribution of UICC amosite and chrysotile measured by this laboratory and to surface and underground mine dusts compiled from du Toit [9]. Figure lb compares fiber tailings from Lake Superior to UICC amosite analysis and to occupational exposures fram du Toit, and figure lc compares the distribution of the longest chrysotile sample measured in urban air in Ontario to UICC and occupational measurements of du Toit. All three cumulative length plots show that distributions for occupational exposure converge with environmental distributions at the 50 percentile level and that the fiber length from occupational exposures are greater than that from environmental exposures at the 99 percentile level. 50 95 99 g9,g Figures la and lb. (caption on the next page). 22

C 5 Figure 1. Oistribution curves showing the difference in asbestos length and other fiber length. (a) About 600 analyses of elongate fibers compared to length distri- bution of UICC samples and from underground (U) and surface (S) dusts from South African Mines. (b) Comparison of amphibole in taconite tailings from Lake Superior to UICC amosite and surface and underground mine dust from South Africa. (c) Comparison of UICC chrysotile and surface and underground mine dusts with sample from atmospheric environment containing largest fibers. See figures lb and lc for figure la labelling of individual distributions. Occupational and environmental samples show a broad length distribution over almost three orders of magnitude, and the only apparent differences in the length distributions are for the longest fraction. Therefore, characterization of the entire length distribution is mandatory for all studies. Campbell, et al. [6, p. 44 ff] have carried out a similar analysis for aspect ratios. They show a great deal of overlap of aspect ratio for the milled asbestos form and the milled non-asbestos form of anthophyllite and tremolite. Furthermore, they show a distinct difference for a commercial milled chrysotile sample and an ambient air sample. In both cases, the distributions overlap, but the milled asbestos form has a small distribution of large length/width aspect ratios that is not found in the milled non-asbestos form, and the commercial milled chrysotile has a small distribution of larger aspect ratios that is not found in the ambient air sample. The aspect ratio distribution of hornblende is very similar to the aspect ratio distribution of the non-asbestos amphiboles. The difference in the aspect ratios between milled asbestos and milled non-asbestos minerals is found for the upper five percent or less. This difference in aspect ratio parallels the difference in length distributions of the largest percentile discussed above for occupational and environmental samples. In fact, the very large aspect ratios would be measured on the fibers of largest length. It may well be that the differences in aspect ratio and of length of the longest fibers will be most significant in health studies. Figure 2 shows the morphology of six different samples of cummingtonite-grunerite from the Wabush Lake, Labrador, area. The bulk composition and the mineralogy are the same for all six samples, and all of the samples were taken within about 500 meters of each other. Figure 2a is clearly an asbestiform sample and figure 2f is clearly equidinensional. The detailed morphology of these samples may show some significant toxicological differences. They are now being studied in detail .ineralogically, and for hemolytic and cell activity responses. 23 0 a w r+ 0 ~ N U

a IIF Mf 4 I5 R A: d r. i~ • a ~ ii ~ • ~ ,,. .~ ,• S• ~ ~ FA Figure 2. Asbestiform and equidimensional cummingtonite-grunerite from Labrador. (a) Asbestiform cummingtonite scale units are in cm. (b) - (f) Variations in fibers, cleavage fragments, and equidimensional cummingtonite-grunerite sampled within 500 meters of each other and the asbestiform variety. Each numbered scale unit is 0.1 cm. fm . 24

CS Fiber Composition Asbestos and other fibers vary in major element composition due to the substitution of octahedral coordinating cations (typically Mg, Fe2 , Fe3 , Al), tetrahedrally coordinated cations (Si, Al), and coordination of larger cations (Ca, Na, K). Chrysotile is a silicate sheet structure of nearly fixed composition, Mg3Si20s(OH)*, but the amphibole asbestos minerals show more substitution of ma~or ions. Hsnce the anthophyllite-gedrite series develops with substitution of Mg for Fe2 , Al for Fe2 , and Mg with substitution of Al for Si makp the charge balance; the cummingtonite-grunerite series with supstitution of Mg for Fe2 ; the tremolite-actinolite series with substitution of Mg for Fe2 and substitution of Fe3+ for Al. "Amosite" is an asbestos acronym for a cummingtonite-grunerite of variable composition, and crocidolite is the asbestos variety for a glaucophane-riebeckite of variable composition. There are other less common amphiboles With asbestiform habit. In addition, there is substitution of trace elements and in some cases other elements (for example, Mn) may substitute in the amphibole structure to a large extent. Therefore, one may not conclude that there is any fixed composition for one asbestos mineral, and it is possible to have variations in composition within one sample depending upon the history of formation of the mineral. In addition, other asbestos minerals and other mineral impurities can and do often occur in asbestos samples. Normally a fibrous sample from an occupational setting or known single source can be identified and characterized quite well even at the micrometer size range. This is possible because there would generally be a limited number of minerals to consider. An environmental sample, however, poses a most difficult analytical task if available in small amounts. There can be many common minerals, each of which may have a variable composition, and the net result is that many minerals may occur with overlap in composition, gross crystallographic properties and optical properties. Health researchers often use well characterized samples from specific locations for their experiments. These samples have been chemically analyzed in bulk, but often individual fibers and variations in composition along a fiber have not been analyzed. UICC samples of amosite and crocidolite as well as one sample of tailings from Lake Superior and one asbestiform cummingtonite-grunerite sample from Labrador (fig. 2a) were subjected to analysis using energy-dispersive fluorescence spectroscopy in conjunction with a transmission electron microscope. The analytical procedure is similar to that of Beaman and File [2]. Isolated fibers between 0.2 - 0.8 pm in width were subjected to analysis with an excitation voltage of 80 kV and a take-off angle of 36 degrees. The excited area was estimated to be about 0.2 pm when considering scattering effects. Counts were recorded and areas under peaks were estimated using a computer routine which also adjusted for background. Ratios of peak area of Mg, Fe, Na, and Ca relative to Si were calculated, and these ratios were adjusted for areal ratios determined on an adjacent blank portion of the grid. This later correction was normally negligible. In the following discussion, ratios of areal peaks to Si corrected for background of analyzer and grid background are reported. Champness et al. [7] have noted that the use of intensity ratios should correct for fluorescence variaTtTons due to specimen thickness variations. Figure 3a shows elemental intensity ratios relative to Si for UICC amosite for 58 analyses on 15 fibers, whereas figure 3b shows similar results for 51 analyses on 15 fibers of UICC crocidolite. In both figures, the results are given for increasing Fe/Si intensity ratios, and the values between horizontal lines represent the intensity ratio value for the particular element. Both samples show a marked variation in elemental intensity ratios with between 30-60 percent variation about the mean f+or the corrected values. With reference to amosite, assuming all of the Fe is structural Fe2 , there should be a parallel decrease in the Mg/Si ratio as Fe/Si increases. This is obviously not apparent for the bulk analysis. Although the surfaces of all fibers were examined prior to analysis for optical density continuity so that surficial material such as Fe-oxides might be excluded, it is possible that some of the variation in the Fe/Si ratio is due to surface oxidation of Fe. But this would not explain the variation in Mg/Si ratios for amosite which, with the exception of two extreme analyses, varies about 20 percent about the mean of the ratio. 25

AmOSiT E (UICC) Mg 9 0.8 Fe FIBERS y O H a -J a ~ z w 2 w -J W CROCIDOLITE (UICC) 1.9 1.8 1.7 6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 n ni u F. nj~ r't_I I U~I A IJ Y . n c B FI BERS Figure 3. Corrected intensity ratios for UICC amosite (a) and UICC crocidolite (b). Intensity ratios are cumulative with the value for each element depicted as the difference between adjacent horizontal bars. 26 I

,4 CS Crocidolite UICC. samples show similar variations with the Fe/Si ratios with a deviation of about 15 percent about the mean; Mg/Si varies about 15 percent about the mean, and Na/Si varies about 25 percent about the mean. There is no relationship between Mg or Na ratios and Fe ratios, but there is an apparent correlation between Na/Si and Mg/Si. This correlation could be due to radiation from Na, Mg, and Al. Figure 4 shows elemental intensity ratios for one fiber of UICC crocidolite (4a) and oqk fiber of UICC amosite (4b). Variation of intensity ratios along the fiber length is between 5-10 percent, and this is much less than for the range in variation for all mineral fibers. This is true for all of the eight mineral fibers tested at multiple locations. CROCIDOLITE (UICC) Ti • K Ca • • • • L • • • ANALYZED SPOTS (CROCIDOLITE FIBER 14rm. diameter 0.3Nm.) Figure 4a. Variation along a fiber of UICC crocidolite. 27

l 1-- Coz F- w zcn ww Cn w a- Ti K Na ~ o_ w Ca ~ Q Mn 0.050 / i 0 !0 ~ ~ 01S ~ M 0090 z Si 0080 w 2 Fe/ 1.000 LL! i AMOSITE (UICC) • • • • I • • • ANALYZED SPOTS (AMOSITE FIBER 16rm dia. 03rm.) Figure 4b. Variation along a fiber of UICC amosite. • d Figure 5 shows the results of 64 analyses on 14 fibers of asbestiform cummingtonite from Labrador. There is an approximate 50 percent variation of Fe/Si intensity ratios about the mean, and there appears to be a decrease in the Mg/Si intensity ratio with increasing Fe/Si ratio with only a few exceptions. t 0 • 28