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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 November 1978) THE DETECTION AND IDENTIFICATION OF ASBESTOS AND ASBESTIFORM MINERALS IN TALC Harold 0. Stanley Pfizer Inc., MPM Divisionl Easton, Pennsylvania 18042 Abstract Concern with the health hazards associated with the presence of chrysotile asbestos and/or the asbestiform minerals in talc has prompted widespread investigation of methods of analysis which would be consistent with good analytical practices. Of all the currently available techniques examined and evaluated, the two most reliable have been found by us to be Step Scanning X-ray Diffraction and Transmission Electron Microscopy (TEM), with Selected Area Electron Diffraction (SAED). The Step Scanning X-ray Diffraction technique allows quantitative detection and identification of tremolite and the asbestiform minerals down to 0.1 percent by weight_ In the absence of chlorite it can detect and quantitatively determine chrysotile asbestos at the 0.5 percent level. Chlorite, however, is often associated with talc ore bodies. When present, chlorite will mask most of the main x-ray diffraction peaks of chrysotile. Additionally, the x-ray diffraction technique cannot distinguish between fibrous and non-fibrous forms of the asbestiform minerals_ TEM is ideally suited to determinations of this type because of its high resolution and magnification capabilities, the morphological nature of the problem, and the mineralogical identification capability through SAED. Key Words: Asbestiform; asbestos; chrysotile; detection; fiber; identi- fication; light microscopy; selected area electron diffraction; talc; transmission electron microscopy; tremolite; x-ray diffraction. Introduction The pneumoconiotic and cancer-inducing health hazards of exposure to the asbestos and asbestiform minerals sometimes found associated with talc have been appropriately identified by recent research, the mass media publications [1-8]2, and the papers heard earlier today. Because of Pfizer's position as a supplier of talc to many industries, we felt that a reliable method of detecting and identifying asbestos and asbestiform minerals possibly present in talc had to be developed. Prior to 1970, we were looking for ,fust such a method. Previous investigators had addressed themselves to the problem of identifying asbestos in bulk form or in airborne samples. We concerned ourselves with detecting and identifying the various forms of asbestos in the bulk talc matrix. As we were to later discover, this is indeed a hostile environment for the analyst. 'Now with Degussa Corp., Rt. 46 at Hollistor Rd., Teterboro, N.J. 07608. 2Figures in brackets indicate the literature references at the end of this paper. Preceding page blank 325

Our goals were: 1. Identifying the mineralogy of our products, specifically, that of our talcs. 2. The unambiguous determination of the crystal habit and crystal structure of the mineralogical species present. Ideally, we were looking for a technique that would be simple and direct, but above all, it was mandatory that the technique be positive and unambiguous. The mineralogical and chemical nature of talc and that of the amphiboles or asbestiform minerals and chrysotile have been adequately described previously at this session. Currently available methods and methodology for detecting asbestos, tremolite, and the asbestiform minerals in the presence of talc were reviewed. Types of analyses which we tried included the following: 1. Infrared spectroscopy 2. Thermal analysis including TGA and DTA 3. X-ray diffraction 4. X-ray fluorescence 5. Adsorption from solution 6. Light microscopy including phase contrast, interference contrast, polarized light, and dispersion staining 7. Electron microscopy including transmission electron microscopy and scanning electron microscopy After initial investigation, the three most likely candidates were; 1. Light microscopy 2. X-ray diffraction 3. Transmission electron microscopy In order to determine which of the above would meet all criteria for the test, we secured samples of pure talc and tremolite from various deposits owned by Pfizer. Samples of pure and carefully characterized asbestos minerals were obtained from the International Union Against Cancer, (UICC), Pneumoconiosis Research Unit, Llandough Hospital, Penarth Glamorgan, United Kingdom. The talcs and asbestiform minerals were examined in the pure or as-received state, their characteristics noted and mixtures made to determine if detection of asbestos minerals was possible at low levels and, if so, what the minimum detection levels might.be. Experimental X-ray diffraction patterns were obtained for all the minerals and mixtures used in this study employing the conventional technique of scanning at rates of 0.5 to 1.0 degrees 2 theta per minute. The samples were then subjected to scrutiny by optical and electron microscopy. During this procedure it was discovered that certain mixtures and mineral species shown to be free of asbestiform minerals by the conventional x-ray diffraction and light microscopy techniques exhibited fairly large percentages (5% or more) of fibrous tremolite and/or asbestiform minerals when viewed by transmission electron microscopy. Oelineation of the reasons for this paradox enabled us to develop reliable techniques for detecting tremolite and the asbestiform minerals at the 0.2 percent level in most talcs by x-ray diffraction. Even lower levels of these minerals are detectable by transmission electron microscopy. Light Microscopy Techniques employing the optical microscope have been used to identify mineral speci- mens for a long time. Techniques that we have examined include polarized light microscopy, transmission light microscopy, phase contrast, and dispersion staining. The difficulty which we encountered in applying these techniques to the problem at hand is that while they work well with pure samples of fairly massive fiber length (3 to 5 microns 326

S45 and larder), observations by transmission electron microscopy have shown that naturally occurring asbestiform minerals often lie below the working resolution of the light microscope. While massive fiber bundles can often be observed by either light or electron microscopy, the observation of individual fibers smaller than approximately 1 micrometer long by 0.02 micrometers wide requires the high resolution capability of the transmission electron microscope. In addition, the limit of detection is confounded by the presence of "apparent fibers" formed when thin talc plates curl up at the edge and roll into a cylindrical morphology. The limit of positive detection and identification of fibers is felt by us to be too high to be of any commercial value. X-ray Diffraction The d-spacings for talc, chlorite, tremolite, and the asbestiform minerals are seen in Table 1. The values given in Table 1 are averaged for pure materials and can shift as much as ±0.02 to ±0.03 nanometers depending upon sample preparation, the level at which the constituent is found in the parent matrix, and the specimens conformity to the idealized chemical composition. While attempting to detect tremolite and the asbestiform minerals in talc at concentrations of two to five percent or below, we found that the normal scanning rate of 0.5 to 1 degree 2 theta per minute was not satisfactory for the following reasons: 1. The noise level was too high providing a detection limit of only a few percent. 2. It was difficult to accurately quantify data from the high noise tracing obtained. Table 1. Principal lattice spacings of talc and related minerals by x-ray diffraction Cu K alpha. - - - - Principal d-spacings in angstroms - - - - Mineral Species 1 2 3 4 5 6 Talc - 9.51 4.73 3.14 2.61 2.50 4.62 Chlorite 14.00 7.03 4.70 3.53 2.82 Tremolite 8.38 3.38 3.12 2.94 2.71 3.27 2.81 2.59 2.53 Chrysotile 7.38 4.55 3.66 2.45 1.54 Amosite 8.26 3.27 3.07 2.77 Anthophyllite 9.50 8.40 4.58 3.25 3.13 3.06 Crocidolite 8.43 4.51 3.43 3.11 2.72 In order to avoid these difficulties, an automated step-scanning method was employed in which the diffractometer was moved in increments of 0.05 degrees 2 theta, and the intensity of x-ray radiation at each step measured for-a total of two minutes. An intensity versus degrees 2 theta plot over the area of interest of 9 degrees to 11 degrees 2 theta was made. Figure 1 shows this step-scan method plotted for a talc which showed no evidence of any asbestos or asbestiform content. Calibration curves were established by integrating the area under the appropriate x-ray diffraction peak of mixtures of I to 10 percent of the species under investigation, the remainder being a sample of talc shown to be tremolite and asbestiform mineral free by the method of transmission electron microscopy to be outlined below. Figure 2 shows this step-scan plot for the one and five percent addition of tremolite to the base talc matrix. Figure 3 shows the calibration curve obtained by this technique for asbestos in talc, and figure 4 shows the same type of plot 327 2063105120

8000 y i ~ ~ ~ ~ ~ 7000 ' , , , , ~ H 6000 p N z 0 5000 i 0 2000 : j 11° 10.50 10° 0.50 9° Degrees 2 Theta Figure 1. Step-scan plot of intensity versus degrees 2 theta for Pfizer, Inc. Montana Talc. 328

8000 s 7000 } 6000 i 5000 4000 3000 / . ~~ 2000 i 11° 10.50 / I / / ! / 1 1 J 1% additi/n of tremolite 11L_ 10.0° 9.5° 9.00 Degrees 2 Theta Figure 2. Step-scan plot of intensity versus degrees 2 theta showing the effect of adding 1% and 5% tremolite to talc. 329

38,000 34,000 30,000 26,000 22,000 18,000 14,000 10,000 6,000 2,000 0 1 2 3 4 5 6 7 8 9 PERCENT ASBESTOS 10 Figure 3. Percent asbestos as a function of intensity of diffracted x-rays. I / Figure 4. Percent tremolite as a E 000 / function of intensity L 4, ( / I fj of diffracted x-ra s. z 0 $ -3,000 330

e g 5 for t`remolite in talc. The minimum detection limit was calculated as that equivalent to three times the square root of the background. For tremolite in talc, the minimum detec- tion limit was found to be approximately 0.2 percent. For chrysotile and the other asbestiform minerals, the minimum detection level obtained by this method is approximately 0.5 percent. This can only be achieved in the absence of chlorite, however. Attempts to remove chlorite by careful acid wash succeeded only in rendering the chrysotile amorphous to the x-ray beam with the result that no x-ray spectrum was obtained in the chrysotile region. Further experimentation revealed that the presence of tremolite at fairly low levels tended to mask or interfere with the detection of some of the other asbestiform minerals. It was thus clear that another technique would be required in these special cases in order to be able to achieve the unambiguous analysis originally required. Electron Microscopy By virtue of its ability to examine individual particles in minute detail and at very high magnifications, the transmission electron microscope has been found by us to provide the technique, ancillary to x-ray diffraction, that is needed to complete the unambiguous detection and identification of asbestiform minerals in talc. The morphology of the asbestiform minerals and tremolite is generally described as acicular or fibrous. This immediately serves to isolate them from the platy talc matrix even in the presence of chlorite, since the chlorite morphology closely resembles that of the talc. If the sample, made into a specimen for the transmission electron microscope, is or can be made homogenous, and a careful examination of approximately 100 different fields of view fails to reveal any fibrous material, then that talc is felt by us to be free of tremolite, chrysotile, and the other asbestiform minerals. The lower detection limit of this technique is difficult to assess since one is often dealing with individual crystals. Figure 5 shows a typical field of view of thp fiber free Montana talc used as a basis of comparison in this study. In order to obtain some idea of the amount of fibrous material in a talc, we carefully counted the number of fibers present in each of 100 fields of view of samples contaminated with 0.1, 0.5, and 1.0 percent by weight of fibrous asbestos. The average number of fibers in each field of view is then plotted as a function of the weight percent of fibers added. A linear relationship is seen to exist between the average number of fibers and the weight percent, as illustrated in figure 6. Table 2 shows the results of the fiber count and the raw data for the calibration curve construction. In the range of 0.1 to 1.0 percent, the linear relationship shows an excellent correlation coefficient [9]. We have plotted data of other investigators up to as high as five percent and found that this linear relationship still holds. An interesting point to note at this time is that the standard deviation for 0.1 weight percent of fibers is more than half of the value of the average number of fibers in the same field of view. Further investigations in our laboratories have Table 2. Fiber count - calibration curve. Weight % fibers Total fibers/100 FOVa Avg. # fibers/FOV Std. deviation 1.0 1183 11.83 7.07 0.5 634 6.34 2.49 0.1 206 2.06 1.39 a FOV = field of view. y= mx + b 3~_b = 2.92 fibers/FOV m= 10.86 Correlation coefficient = 0.99997 b = 0.95 331 V

Cp Figure 5. Pfizer, Inc. Platy Montana Talc. Bar is one micron. N O 01 332 W f.+ 0 ~ ..

w w 12 10 4 2 1 I I I I I I I I__ 0.1 0.2 0.3 0.4 0.5 0.6 0.9 0.8 0.9 1.0 Weight Percent - Fibers in Talc Figure 6. Fibers in talc. 9ZiS0i£90Z

convinced us that this linear relationship does not hold much below 0.1 percent. This is intuitively obvious upon an examination of figure 6 which, you will remember, does not pass through the origin. Somewhere below 0.1 weight percent of fibers in the talc, the linear relationship no longer holds, and the line curves down through the origin. Repeated examinations have confirmed the fact that the Montana talc used in this study is fiber free. Below 0.1 weight percent the data must become so scattered as to be meaningless on a statistical basis. A typical field of view of a Montana talc which was doped with 1.0 percent chrysotile fibers is seen in figure 7. A semi-qualitative estimate of the weight percent fiber content can be easily obtained by reference back to the calibration curve. It is mandatory, however, that the samples under investigation be prepared in exactly the same manner as the samples used in the original calibration curve construction. It is also mandatory that one be certain of the homogeneity of the calibration samples and the Figure 7. Commercial talc product with a 1% addition of chrysotile asbestos. Bar is one micron. 334

sample under investigation. Great care must be exercised in the sample preparation, or the results become totally meaningless. Figure 8 shows a commercial talc in which approximately one percent of naturally occurring chrysotile was obscured from detection by the method of x-ray diffraction because of the presence of chlorite. w Figure 8. Commercial talc with naturally occurring co-deposits of chlorite and chrysotile asbestos. The asbestos is present at approximately the 1% concentration level. Bar is one micron. 335

1 Selected area electron diffraction was used in conjunction with the examination of morphology. Using this combined method, a single crystal or particle can be selected and analyzed. Single particles usually yielded spot patterns, but if a group or bundle of fibers was found and would transmit electrons, a polycrystalline ring type pattern would result. The use of selected area electron diffraction is mandatory to prove that the pseudo fibers of talc caused by plate-edge curling and talc plates on edge were actually talc, and not tremolite or an asbestiform mineral. A comparison of selected area electron diffraction patterns of these pseudo-fibers to that of the talc platelets showed that the identical compound, talc, was the only species present. Table 3 lists the principle electron diffraction maximum for talc, tremolite, and the asbestiform minerals [10]. In almost all cases, many more spots or rings were observed than are reported here. In Table 3, only the strongest lines which are the ones most likely to be observed have been tabulated. Table 3. Selected area electron diffraction maxima for talc and related mineralsa (in angstroms). Talc Tremolite Chrysatile Amosite Anthophyllite 4.60 4.51 4.58 3.88 4.58 2.62 2.59 3.67 3.45 2.65 2.32 2.53 2.61 3.00 2.27 1.74 2.32 2.14 2.64 1.75 1.59 2.27 1.70 1.74 1.55 1.53 2.04 1.55 1.61 1.33 1.33 1.86 1.34 1.55 1.28 1.28 1.69 1.29 1.32 1.23 1.65 a The data for chrysotile, amosite, and anthophyllite were taken from reference [11]. Conclusions The present work has shown that properly prepared samples of talc can be examined by x-ray diffraction to detect tremolite at levels down to 0.2 percent and chrysotile at the 0.5 percent level in the absence of chlorite. In the presence of chlorite, and at concen- tration levels lower than those stated above, the transmission electron microscope was found to provide reliable detection and identification of fibrous tremolite and the asbestifors minerals. The transmission electron microscope is the most sensitive we have found, and appears to be a more or less referee technique since, when morphology observations are coupled with selected area electron diffraction studies, there are no known interferences. light microscopy was helpful only in screening samples with large particles and high concentrations of objectionable fibers. Using the above techniques, we have been able to screen large numbers of talc speci- mens. We have been able to detect chrysotile and/or tremolite and the asbestiform minerals at levels down to 0.1 weight percent of fiber. We have been able to detect the asbestiform minerals in low concentration specifically by transmission electron microscopy with selected area electron diffraction, when the presence of the asbestos was masked by the presence of chlorite (which was also present at less than 5% concentration). We, there- fore, feel that we have a technique that allows us to detect and identify chrysotile fibrous tremolite, and asbestiform minerals at concentrations down to 0.1 percent by weight. 336

c, S References [1] Cralley, L. J., Key, M. M., Groth, D. H., Lainhart, W. S., and Ligo, R. M., Fibrous and mineral content of cosmetic talcum products, J. Amer. Indus. Hyq. Assoc., 29, 350 (1968). [2] Hogue, W. L. Jr. and Mallette, L. S., A study of workers exposed to talc and other dusting compounds in the rubber industry, J. Indus. Ea. Toxical. , 31, 359 (1949). [3] Smith, K. W., Plumonary disability in asbestos workers, Arch. Ind. Health, 12, 198 (1955). [4] Schepers, G. W. H. and Durkan, T. M., The effects of inhaled talc-mining dust on the human lung, AMA Arch. Indus. Health, 12, 182 (1955). [5] Brodeur, P., The magic mineral, New Yorker Ma aZine, p. 12, October 1968. [6] Merliss, R. R., Talc-treated rice and Japanese stomach cancer, Science, 173, 1141- 1142 (1971). [7] Sax, N. Irving, Ed., "Talc", dangerous properties of industrial materials, Reinhold Publishing Corp., New York, 1963, p. 1217. [8] Sax, N. Irving, Ed., "Talc", dangerous properties of industrial materials, Reinhold Publishing Corp., New York, 1963, p. 469. [9] Stanley, H. D., The detection and identification of asbestos and asbestiform minerals in talc, 34th Annual Proceedings of the Electron Microscopy Society of America, p. 618-619, August, 1976. [10] Timbrell, V., Characteristics of the International Union Against Cancer Standard Reference Samples of Asbestos, Proc. Int. Pneumoconiosis Conf., Johannesburg, 1969. 337 w 0

Discussion ,1. SCHELTZ: As the spokesman for the Cosmetic, Toiletry, and Fragrance Association, I would like to make several comments. First: In a survey conducted recently by that organization among its member companies, some thirty-four hundred samples of cosmetic talc from both domestic and international sources were analyzed and not a single sample was found to contain chrysotile asbestos. We are aware that the spiking of chrysotile asbestos into talc can be analyzed effectively by x-ray diffractometry. These samples of talc are cosmetic which, by definition, means that they contain at least 90 percent of the actual talc mineral species. I would also like to comment on quantitative analysis of amphibole minerals, by x-ray diffractometry. While x-ray diffractometry is a good technique to detect amphibole minerals, one needs to be very cautious in attempting to perform a quanti- tative analysis. I think Dr. Haartz from NIOSH just pointed out that there are major differences based not only on compositional variations, but also morphological character- istics that make not only peak heights but also integrated peak intensity variable. So, while x-ray diffractometry is a good method for detection, it is not necessarily good for quantitative analysis. I would also like to point out that the Cosmetic, Toiletry, and Fragrance Association is currently undertaking an extensive analysis of consumer talcum products for the traces of amphibole minerals. H. STANLEY: As I understand it, your first point is that x-ray diffraction is not particularly quantitative for determination of amphiboles in talc. We haven't found that to be the case in our laboratory, and I think there are a number of people here that I have been talking to the last several days that have had the same experience. The x-ray diffraction is good if you want to know, for example, the total amount of tremolite present, but if you want to know if some of that tremolite is fibrous, then as I attempted to point out, you have to go to transmitted electron microscopy with selected area diffraction. SCHELTZ: That's exactly my point. ..... (rest inaudible) ..... As to the second point, we were talking about cosmetic grade talc of at least 90 per- cent purity, the purity of the Montana talc is in excess of 96 percent, so I understand your point. 338