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FILE NAME Talc TALC DATE 1974 Dec DOC TALC050 DOCUMENT DESCRIPTION Journal Article - Identification and Quantitation of Asbestos in Talc Environmental Health Perspectives Vol 9 pp 95-109 1974 Identification and Quantitation of Asbestos in Talc : by Arthur N. Rohl and Arthur M. Langer The currently used analytical methods for identification characterization and quantitation of asbestos fiber in consumer talcum products include polarized light microscopy ray diffraction analysis transmission electron microscopy with selected area electron diffraction and elec- tron microprobe techniques Light microscope methods have severe limitations imposed by the ultimate size resolution of the optical system Small particles go unresolved those marginally resolved may possess optical properties different from those properties cited in the literature most optical properties e.g. indices of refraction are difficult to measure on small particles In addition to these difficulties talc fibers often possess optical properties different from those of talc plates which further confound analysis Light microscopy is recommended for use only as a preliminary tool on limited large samples Transmission electron microscopy is a good standard technique for visualization of contaminant asbestos fibers Together with selected area electron diffraction talc fibers may be easily differentiated from amphibole asbestos fibers on the basis of both morphological and structural characterization Chrysotile fibers are easily distinguished on this basis as well The amphibole asbestos minerals require chemical characterization to differentiate among the different fiber types Probe analysis is mandatory for such fibers The major drawbacks to electron beam instrumentation for the mineralogical characterization of talcum products are the time and effort required for data acquisition These techniques do not lend themselves to routine study ray diffraction analysis utilizing the scan method offers a relatively rapid quantitative technique for gross fiber analysis Based on comparison with standard specimens the fiber content of talcs may be quantitatively determined It is essential to employ a specimen preparation technique which yields homogeneously dispersed particles Tremolite may be determined at levels as low as 0.10 by weight chrysotile 0.25 and anthophyllite at 2.0 by weight occurrence in talc The variance of these values depends upon many factors including the mass absorption coefficient of the fiber types as compared to talc and selected diagnostic reflections and their relative intensities Each of the above techniques is described in detail A method for routine analysis of consumer talcum products is suggested Introduction The mineral talc is a monoclinic occasionally triclinic hydrated magnesium sheet silicate with the ideal formula Mg6Si8O20 Although a magnesium silicate it frequently contains small amounts of iron and other trace metals in the structure It can occur in several crystal habits from plates to fibers 1 2 In most talc deposits plates tend to be far more Environmental Sciences Laboratory Mount Sinai School of Medicine of the City University of New York New York 10029 common than fibers The term fibrous talc im- plies mineralogically talc occurring with a fiber habit form As used in the medical literature fibrous talc is synonymous for tales containing any fiber including asbestos Geologically talc occurs in rock masses often coexisting with a large number of other hydrated magnesium silicate mineral species 3 4 This latter observation is based on mineralogical analysis of naturally occurring talc deposits and laboratory studies of tale crystallization Frequently these coexisting mineral phases are asbestos Table 1 95 December 1974 Table 1. Talc and its associated asbestos minerals Empirical formula Common chemical substitutions Structure and habit Crystal system Talc Mg6Si8O20 Fe for Mg Al for Si Tremolite Ca2Mg5Si8O22 Fe for Mg Mn for Mg Na for Ca Anthophyllite Mg6Fe Fe for Mg Al for Si Chrysotile Mg6Si4010 Fe for Mg Ni for Mg Sheet silicate plates common fibers com- mon forms massive foliated aggregates intergrowths on submicron scale many tale fibers observed in platy tales on submicron scale Chain silicate fibers common often as massive aggregates forms intergrowths in some tales on submicron scale fibers tend to short and stubby size ranges from visible by eye to sublight microscopic Chain silicate fibers common columnar or fibrous aggregates forms intergrowths in some talcs fibers tend be long and thin size ranges from visible by eye to sublight microscopic Sheet silicate curved sheets form fibers often as compacted fibers in pseudo foliated masses especially in serpentine rock forms interplanar interlaminar contaminant in talc plates fibers in talc tend to be sublight microscopic in size Monoclinic triclinic Monoclinic Orthorhombic Monoclinic orthorhombic Cleavage Optical properties nx Nz Parallel perfect nations to plate 001 prism termi- Parallel and across fiber axis 110 perfect Parallel and across fiber axis perfect Parallel to fiber axis 001 for clino variety 1.539-1.550 1.589-1.600 Indices fibers higher 1.581-1.615 1.601-1.641 for 1.596-1.654 1.625-1.666 1.532-1.549 1.545-1.556 Indices lower for low- iron chrysotiles Mass absorption coefficients Cuka = 1.542 a Occurrence 1032 1335 1072 y a . 717 Generally present as the major mineral in commercial tale Common contaminant in many tales in carbonate rocks Often a contaminant in tales in carbonate and serpentine rocks Occasional contaminant in talcs especially in serpentine rocks Other minerals commonly in tale Carbonates e.g calcite micas e.g. phlogopite clays e.g. montmorillonite chlorite feldspars e.g. andesine quartz serpentine e.g. antigorite spinels e.g. magnetite a All coefficients calculated on the basis of the empirical formula for each Talc rocks those commercially worked for ore material may form as the result of two major geological processes hydrothermal alteration of preexisting mafic rich rocks and lowgrade hydrothermal metamorphism of siliceous dolomite bearing rich rocks These processes are geologically referred to as steatitization and serpentinization They involve slightly different original bulk chemical compositions and end mineral products Both may produce significant amounts of asbestos minerals chrysotile in serpentinization and amphibole asbestos minerals in steatitization The metamorphism of siliceous dolomites almost invariably results in the formation of the asbestos mineral tremolite 2 During geological alteration of rocks new mineral phases are frequently created from preexisting ones Most commercial talc deposits are formed as the result of such processes These deposits may consist of grained intimate mixtures of minerals especially talc and asbestos In addition to the mineral complexities of tale deposits these ore bodies are often zoned That is the mineral composition and assemblage reflecting changes in bulk 96 Environmental Health Perspectives chemistry varies over short distances several feet to several inches This invariably means that the mined talc ore consists of mineral mix- tures since mineral phase separation is difficult if not impossible to achieve during mining The complexity of mineral deposits may be illustrated by a recent paper on the mineralogy and mineral paragenesis of the New York State talc deposits in the Gouverneur district 5 Because commercial talc deposits consist of natural admixtures of minerals a number of mineralogically different materials have been used as commercial talc The mineral talc is naturally soft and may be physically reduced in size with little mechanical effort because of the weak bonding forces between adjacent unit sheets The material possesses a number of properties making it useful in hundreds of applications 6 Many of these applications however require small particle sizes high surface areas and good surface sorption characteristics Therefore many of the talc products must be grained but need not be pure The result is a requirement for a talclike rock rather than pure tale Therefore talc as used in industry does not refer to the mineral species talc but rather to a property 7 A number of materials have been used as syn- onyms for tale asbestine talc steatite soapstone tremolite talc French talc fibrous talc All of these materials may contain quantities of asbestos fiber In 1973 there were 38 major tale producers in the United States talc was mined in 10 states The geological rock types from which these materials were mined covered the entire spec- trum of geological possibilities For example in St. Lawrence County New York State 30 or less of the materials recovered as talc is the true mineral talc 5,6 In this deposit the amphibole asbestos minerals tremolite and anthophyllite as well as serpentine including the mineral chrysotile occur throughout 5 Therefore the purity of any commercially available talc in the United States is related to both the nature of the original talc deposit and the extent to which the rock is upgraded to eliminate contaminant minerals This latter process is often referred to as beneficiation Some mineralogical analyses have been made of commercial talcs One such study showed of the 51 tales studied none was 100 tale 7 The asbestos content of these materials ranged from 0 to 87 Studies of New York State talc deposits and their asbestos contents have been carried out Mineralogical analyses of these materials indicated all samples were predominantly asbestos 8 In another study in which 22 available consumer talcum products were examined it was found that fibrous constituents were present in all of the samples 9 Biological Consequences of Talc Dust Exposure Exposure to tale dust in intensity equivalent to an occupational exposure has been shown to be associated with a diffuse interstitial lung scarring which has been termed talcosis 10-16 However even in these studies some questions were raised as to the specific pathogenic agent in the talc itself For example asbestos bodies were frequently observed in the lung tissues of individuals who died of talcosis 11 13 17 clinical and radiological similarities existed between the disease asbestosis and talcosis 12 13 18 and fibrous talc appeared to be more pathogenic than platy talc 19 Several investigators using the individual mineral components of fibrous talc made up of mixtures of tremolite asbestos and platy tale observed different biological responses to the components in animals They observed that the asbestos component induced a greater fibrogenic response in the animals 20 One investigator has also reported an increased incidence of neoplasia amongst talc miners and millers exposed to containing talc dusts 21 Lung tissues from workmen exposed to talc dust have been analyzed in our laboratory Both amphibole and chrysotile asbestos fibers were observed in these tissues by electron microscopy 22 Several recent studies involving experimen- tal animals and observations on human materials have shown that exposure to asbestos and talc may be associated with tumors of the ovary and cervix 23 24 In addition the use of such talcum products as lubricants drying agents and excipients in a number of food and food packaging products may pose a hazard in terms of an increased neoplastic risk in the gastrointestinal system through ingestion 25 December 1974 97 Asbestos Content of Consumer Talcum Products Because the mining of talc almost invariably includes the mining of asbestos as well this natural asbestos contaminant in tale may be carried over into the consumer product Since asbestos has been suspected as the pathogenic agent in tale workmen low levels of asbestos in consumer talcs have been the focus of many recent studies These data and observations lead to an important public health question is asbestos present in consumer tales and if present which fiber type and in what concen- trations Instrumental Methods of Identification of Asbestos in Talc There are a number of standard mineralogical techniques which may be used for identification and quantitation of asbestos fibers in talc These include light optical methods electron optical techniques and ray diffraction techniques Light Microscopy The most widely used and inexpensive instrumental technique for the analysis of mineralogical specimens is optical microscopy A microscope which employs polarized light optics has been a standard technique for identification of minerals for the past century When used with immersion oils not only may phases be identified but the bulk chemistries of the phases may be determined with remarkable accuracy The field of optical mineralogy has been properly termed optical crystallography in that the information obtained may be elegant and quantitative The analyses of the light visible mineral phases within tales may be made with this method We have examined numerous tales by means of light microscopy Powders from different sources ca. 0.5 mg both natural and man- made were placed on precleaned glass slides and immersed in mounting nD = 1.500 1.550 1.600 Several splits from each sample were examined for their optical properties The microscope employed in all cases was equipped with bright field illumination and polarized light optics An overall view of various proper- ties of the material was obtained at this level of investigation relative relief birefringence gross morphology and extinction angles of fibers were observed or measured The relative purity of each sample was observed and the general size distributions of the mineral phases were determined Fig 1 The identified mineral phases tended to be grained However when the talc samples are grained and contain talc fibers some problems are encountered Specifically the normal birefringence characteristics may not be present for the fibers indices of refraction are difficult to measure differentiation of internal reflec- tance and Becke line when viewed with central illumination talc fibers have higher indices of refraction than talc plates and may be confused with amphiboles especially small fibers of tremolite fibers are difficult to routinely resolve from tale plates when the latter are oriented on edge especially at high magnifications many fibers are too small to see by light microscopy , In summary light microscopy employing polarized light optics has severe limitations for critical analysis of talc specimens for asbestos fibers The inherent limitation of optical microscopic resolution may so restrict the analysis that large numbers of small fibers may go undetected It is a paradox however that op- tical microscopy is well suited for determining the presence of other contaminants in talc e.g. the carbonate minerals and other silicate phases quartz feldspar micas etc. Also it is remarkably sensitive for the determination of trace mineral phases if they are present in sizes resolvable by light optical systems This method although limited is recommend as a preliminary tool of investigation 26 Ray Diffraction One of the standard mineralogical techniques used in the analysis of solid crystalline phases is ray powder diffractometry With this method those phases with crystallite sizes greater than 2000 ^ may be subjected to ray bombardment and made to reflect from their atomic planes an ray spectrum characteristic of their interatomic distances and chemical makeup This in effect is a structural fingerprint and serves to identify in most cases uniquely the nature of the phases present in the sample Additional information may be obtained by ray powder dif- 98 Environmental Health Perspectives FIGURE 1. Photomicrographs of a tale sample from New York State A talc in plane polarized light shows granularity and small size of pulverized sample D consecutive photos of pulverized samples between crossed polars show the presence of prismatic crystals Several edge plates may be confused with fibers Some of the larger crystals on the basis of their optical properties were identified as tremolite fractometry including quantitation of the individual phases present in a crystalline matrix and their average particle size 27 ray diffraction is considered to be a more sophisticated tool than the polarizing microscope Although less sensitive the electron microscope for the detection of trace quantities of materials present in a matrix this instrumental technique is commonly used for the analysis of talcs The difficulties and nuances involved in the ray analysis of talc for trace asbestos fiber are many We describe these below and outline what we consider to be an acceptable analytical technique This technique consists of the preparation of tale standards talc matrices admixed with known quantities of fiber the selection of characteristic ray reflections to be scanned sample preparation to insure homogeneity and reproducibility and instrumental technique Preparation of Standard Dilution of Asbestos Minerals in Talc for the Purpose of Quantitative Ray Analysis The identification and quantitation of asbestos fiber in talc by ray diffraction techniques may be achieved by comparison of known dilutions fiber type and quantity of asbestos in a tale matrix with unknowns The preparation of standard known dilutions of asbestos minerals in talc for quantitative analysis requires 1 a talc matrix completely free of contaminating asbestos minerals 2 pure asbestos fiber as the sought contaminant phase 3 a preparation method for insuring homogeneity and reproducibility of the standard dilution material i.e. identical aggregate December 1974 99 geometry 4 selection of diagnostic ray reflections with no superimposed interferences Selection of the Talc Matrix Mineral Various types of talc were tested for possible use as pure reference material including pharmaceutical excipient and additive tales acknowledged high purity grade Screening of tales was made by ray powder diffraction analysis For each of the talc samples a continuous scan from 3 to 60 at the rate of min was made in order to rapidly identity the major mineral phases particularly asbestos minerals If no asbestos phases were detected the material was examined in the scan mode with a scanning rate of 0.02 20 in the diagnostic asbestos reflection regions Table 2 If no asbestos was detected by this method the absence of asbestos was further verified by transmission electron microscopy Typically specimens were scanned at 42,000 direct screen magnification to insure the detection of chrysotile fibrils By using these screening techniques a tale which was apparently free of asbestos was selected as the matrix material During the course of this screening it was found that many tales contain varying amounts of the hydrous magnesium silicate mineral chlorite The presence of this mineral interferes with the detection of small amounts of chrysotile The presence of chlorite is indicated by strong ray basal reflections 14.2 ^ 001 7.1 ^ 002 This latter reflection occurs in the same general area as does the 002 reflection of chrysotile 7.3 ^ Therefore a higher- order reflection was chosen for the purpose of resolving these mineral phases Selection of the Asbestos Fibers In addi- tion to selecting a tale of high purity it was necessary to obtain asbestos mineral samples which were themselves free of contamination This would ensure a high quality asbestos dilution The reference asbestos minerals of the International Union Against Cancer UICC were found to be generally suitable for this purpose 28 The reference anthophyllite and tremolite were micropulverized and analyzed for purity by scanning ray analysis and by transmission electron microscopy in accordance with the procedures previously described for talc The fibers were found to be free of in- terfering contaminants The chrysotile specimen used in making the chrysotile dilutions was a triple air jet milled sample from the Jeffrey Mine Quebec provided chrysotile Manville Corp. Sample Preparation Among the problems of specimen handling for diffractometer analysis are the effects of particle size pre- ferred orientation and surface flatness In the preparation of the asbestos standards par- ticular care was taken to ensure that the samples had a uniform size distribution and an effective crystallite dimension on the order of five microns or less This was done in order to reduce the mean deviation of reflection inten- sities to a value of about % 29 The reproducibility of reflection intensities is strongly influenced by the degree of cleavage of crystalline powders Talc which possesses perfect cleavage parallel to its basal plate Fig 2A will tend preferentially to orientate parallel to this direction when the sample is packed into the holder Fig 2C This will occur even when crystallite size has been greatly reduced by grinding 27 29 In addition to plate orientation one can easily envisage how admixed fibers can orient with their fiber axis parallel to the plates Figs 2B 2D FIGURE 2. Preferred orientation A talc plate 001 and B anthophyllite fiber 210 C prepared talcs tend to align themselves parallel to their basal plates the 001 cleavage D anthophyllite fibers in tale matrices tend to align themselves with their 210 surfaces parallel to talc 001 cleavages Crystallographic axes marked a b c C and D looking parallel to talc plates A number of techniques have been developed for reducing preferred orientation orientation effects in- cluding binder and slurr red methods sifting and backloading rs and 100 Environmental Health Perspectives various other techniques 27-31 Several such preparation methods were tested for use in the present study None were found to give satisfactory reproducibility as indicated by the variation deviation of reflection intensity of duplicate dilution standards which had been uniformly prepared and mounted The lack of success in this regard was taken to indicate that in mixtures of minerals with platy or fibrous habit a statistically random distribution of orientations is extremely difficult if not impossible to achieve Accordingly a technique was developed which was intended to obtain a high degree of sensitivity for substances present in minute quantities and more important which had a greater degree of reproducibility of reflection intensities Binary systems of chrysotile tremolite and anthophyllite in tale were prepared at varying levels of dilution on a weight per weight basis The following per cent concentrations of fibers in talc were initially prepared for each binary system 5.0 4.0 2.0 1.0 0.5 0.25 0.20 0.10 The standard weight of the total sample was 50 mg The weighed asbestos mixtures were prepared in 10 ml of filtered water to avoid any possible contamination utilizing a surfactant and ultrasonic energy to disperse the phases homogeneously This slurry was poured immediately into a 30 hypodermic syringe and filtered through a mm diameter 0.22 ...m effective pore size membrane filter A standard filter holder for attachment to a hypodermic syringe is available Fig 3 from the Millipore Co. In the course of filtering the syringe is held in a horizontal position and is frequently rotated and shaken This action helps to prevent size and density separation of the suspended particles The residue forms a cake of uniform thickness of about 0.5 mm on the membrane filter and the resulting surface of the filter cake is flat The cake is allowed to dry and then is glued to a glass microscope slide for ray powder diffraction analysis ray analysis of the dried cake on repeated preparations shows that the mineral phases are homogeneously distributed throughout This technique has the advantage of uniformly preparing mounting and measuring the asbestos dilutions under identical conditions The reproducibility and sensitivity of the technique is demonstrated by a comparison of the measured areas of index reflections for a number of samples Table 3 FIGURE 3. Device used to prepare filter cakes of standard dilutions of asbestos fibers in talc A holder which accommodates the membrane filter B holder and gasket attachment to syringe C syringe D plunger Selection of Ray Reflections In order to detect the weak reflections of dilution components it was necessary to scan in a stepwise manner across a preselected area of the ray profile Because of structural similarities in the minerals under examination there was much overlapping or interference in many reflections Table 2 Fig 4 The similarities in crystal structure and the consequent overlapping and interference of the ray diffraction reflections of talc chrysotile anthophyllite and tremolite have been mentioned This condition made it necessary to select a reflection or set of reflections for each mineral component which could be used unambiguously as an index or indices of Table 2. Diagnostic reflections of asbestos minerals used in standard dilutions Mineral ^ Anthophyllite 8.26 Chrysotile 3.66 Tremolite 8.38 hkl 210 004 110 / 55 80 100 20 'Scan 20 10.65 10.1-11.1 24.31 23.5-27.5 10.55 10.0-11.1 For each characteristic interplanar spacing given the Miller Index relative intensity Bragg reflection angle and scan interval are included December 1974 101 Table 3. Replicate measurements of areas of diagnostic peaks of chrysotile in chrysotile dilutions Specimen Peak areas in. A B 99.5 Talc chrysotile Avg 2.20 2.17 2.18 2.18 2.19 2.17 2.19 2.18 99.75 Tale chrysotile Avg 0.84 0.88 0.84 0.84 0.88 0.88 0.88 0.88 99.9 Talc chrysotile Not detected Not detected a Measured with compensating polar planimeter peaks plotted on same scale on scan runs under constant settings 2 ^ 10cps 0.02 20 45 kV mA ( 12 FIGURE 4. ray diffraction tracings of fibrous talc samples from New York State in the 8-16 20 region of reflections S serpentine includes the minerals chrysotile lizardite antigorite A anthophyllite Tr tremolite T talc M mica phlogopite C chlorite Note that the anthophyllite peak at 8.9 ^ 020 is often masked by a strong talc peak at 9.3 002 the anthophyllite 8.26 ^ 210 peak is often masked by the tremolite 8.38 A 110 peak The tremolite peak in this figure masked almost % anthophyllite I intensity the amount of that mineral present in a mixture This was done by a comparison of the ASTM Ray Powder Data File for each of the minerals and by indexing the diffractograms of each of the UICC asbestos minerals and the reference talc When this data was assembled and compared it was possible to select reflections unique in d spacing and strong enough in intensity to be used as quantitative indices Table 2 In this way certain diagnostic or in- dex reflections for each of the dilution com- ponents were selected and these angular intervals were ray scanned at 0.01 and 0.02 20. A digital printout of elapsed time in a fixed- count determination was used to prepare precise positions and profiles of the diagnostic reflections In the fixed count mode the diffractometer scans equal angular intervals 0.02 20 accumulating fixed counts at each point with equal accuracy Although weak reflections require longer times than higher intensity reflections all points are determined with equal precision In this method the statistical accuracy of any measured count depends only on the total number of counts recorded The number of counts was calculated by taking the reciprocal of counting times The counting rates were selected to give a uniform percentage probable error of about 2.0 When the number of counts is plotted as a function of 20 a profile of the diagnostic reflection is found Fig 5 The area above background determined with a compensating polar planimeter is taken to be proportional to the reflection intensity Factors Affecting the Limits of Detectability of Substances by Ray Diffraction In a mixture of powders the resulting ray diffraction pattern consists of the superposition 102 Environmental Health Perspectives 3.633.63"" 80 CHR 004 6 COUNT COUNT COUNTCOUNT 000 COUNT 000 9 3.53 RAY 00 000 CHL 004 X Pe -- ---- -- ---- 20 25 26 FIGURE 5. Step profile obtained on a standard dilution of % chrysotile in a 99 talc matrix Note the contamination of talc with a trace of chlorite 3.53 reflection scan obtained at 0.05 20 for 2000 counts of diffraction patterns of the constituent com- pounds Fig 4 The intensity of each com- pound's pattern is proportional to but not necessarily a linear function of its concentration 29 Aside from instrumental factors e.g. change in ray output from target tube which may influence the profiles of diffraction max- ima there are a number of other factors to be considered These are related primarily to the material including sample homogeneity chemical makeup particle size preferred orientation sample thickness and flatness and ab- sorption characteristics ' General Factors The components of a mix- ture and their relative amounts may be deter- mined by the intensity measurements of the dif- fraction patterns if all these factors are con- sidered However it is necessary that certain conditions be satisfied The component sought must be homogeneously mixed in its matrix and consist of randomly oriented small particles to insure that a large proportion of them will satisfy the Bragg geometry for reflection It has been shown that with materials of intermediate atomic number 12-30 particle sizes in the range of 2-10 ...mwill give a reproducibility of greater than % 27 29 A uniformly small particle size will also help to minimize particle orientation and microabsorption effects Comparative intensity measurements also require that the porosity of the specimen is constant and that the specimen is thick enough to diffract xrays with maximum intensity The powdered materials used in this study and the mounting technique of specimen preparation were selected in order to fulfill these basic requirements of quantitative ray diffraction analysis Special Factors An important factor which affects the ability to detect small amounts of material by ray diffraction analysis is specimen ray absorption This oc- curs when two substances with different mass absorption coefficients are mixed The mass absorption coefficient ... is a measure of the fraction of the energy in the incident ray beam absorbed when a beam of unit cross section traverses a unit mass of material It is useful because it is characteristic of the chemical elements in the absorbing material and is essentially independent of their chemical or physical aggregate state It is a function only of the wavelength of the absorbed radiation and the atomic number of the absorbing element The sensitivity of detection of a component may vary considerably depending on / for the component relative to that of the matrix The mass absorption coefficients of talc chrysotile anthophyllite and tremolite for the wavelength of copper radiation 1.542 A ) are given in Table 1. Chrysotile has the lowest / of the four minerals about 717 which is about 7/10 that of talc 1032. Thus the sensitivity of detection of chrysotile in talc is greater than that of the other two asbestos minerals neglecting the effects of such variables as particle size and degree of crystallinity which may have equal or greater influences on the sensitivity of detec- tion The precision reproducibility of intensity measurements obtained in ray diffraction analysis can be optimized by a suitable counting strategy If an accumulated count of December 1974 103 105-5 is obtained the precision of the relative intensity measurement due to counting statistics alone is N 1/2 The determination is also related to specimen preparation reproducibility With specimens having an average particle size of 1-2...m the range in intensity measurements is from 0.1 to 0.5 The overall precision of quantitative ray analysis will probably lie in the range of 0.5 to 1.0 27 The accuracy of ray analysis depends in large measure on the degree of preferred orientation of particles in the sample The materials used in this study sheet silicates and fibers can be expected to have a high degree of preferred orientation This inescapable physical limitation is the main factor in controlling the level of ac- curacy Standard Dilutions Chrysotile in Talc The presence of chlorite in the talc standard used in preparation of chrysotile dilutions may preclude the use of the 002 reflection of chrysotile as a diagnostic reflection The chlorite reflection at about 12.6 20 overlaps and masks the latter reflection When the intensities of these two reflections are about the same the peaks can be resolved with a scanning rate of 0.01 per degree 20. Except for this special condition the peak background ratio of the chrysotile 002 does not permit it to be measured with precision If chrysotile and chlorite are both present in the sample but chrysotile predominates then the 002 peak of chrysotile can be used as an indicator of the relative amount of chrysotile pre- sent Another mineral which may interfere with the detection or quantitation of chrysotile is kaolinite This mineral is the most common member of the kaolin group of hydrous aluminum silicate clay minerals Although kaolinite has not been reported in talc or serpentine rock particularly because the modes of formation and geochemical environment are quite dissimilar this fact does not preclude the presence of kaolinite in industrial or consumer talcum by admixing The mechanical and physical properties of kaolinite would be in harmony with those of talc In fact it has been identified as component of some cosmetic talcum products Because there are close struc- tural similarities between chrysotile and kaolinite their ray diffraction patterns are similar in many respects The order basal reflection of kaolinite at 7.15 ^ may thus overlap or mask the chrysotile 002 reflection at 7.24 ^ . Depending on the relative amounts of these two minerals present chrysotile may be neither detectable nor quantitatively deter- mined with precision by use of the 7.24 ^ reflec- tion It has been found that the 3.63 004 reflection of chrysotile at 24.3 20 is more useful than the 002 reflection for detecting the dilutions of that mineral in tale matrices This chrysotile reflection is better resolved from reflections of associated minerals particularly from the 3.53 ^ 004 reflection of chlorite at 25.1 20. The background ratio of the chrysotile 004 line which has an intensity of about 8/10 of the 002 reflection is thus used to determine the minimum detectable amount of chrysotile in tale standard samples The samples are scanned at a rate of 0.02 per degree 20 from an angle of 23.0 to 27.0 20 in order to achieve maximum peak and minimum background intensities in the same region of the spectrum A minimum of 0.25 by weight of chrysotile in standard talc has been detected consistently Chrysotile at lower levels of dilu- tion cannot be detected Tremolite in Talc A few specimens labeled as tremolite were prepared for ray powder diffraction analysis and continuously scanned from 3 to 60 20 at a rate of min When these spectra were indexed it was found that only one tremolite sample was free of contaminants That is the positions and relative intensities of all of its reflections compared exactly with the data given for an ASTM reference tremolite American Society for Testing Materials standard powder diffraction file 13437 As indicated in Table 2 the 8.38 reflection of tremolite which has a relative intensity of 100 was selected as the diagnostic reflection for the tremolite dilution series The 3.12 ^ tremolite reflection which also has a relative in- tensity of 100 was not used because it overlaps with the 3.12 ^ reflection of talc Dilution levels from 99.0 talc tremolite through 99.95 0.05 tremolite were prepared and step- scanned under constant instrumental con- ditions The diagnostic reflection of tremolite was detected at all levels of dilution up to and 104 Environmental Health Perspectives including the 99.9 talc tremolite level Less than 0.1 tremolite was not detected above background Replicate dilution mixtures at the 0.1 and 0.05 tremolite levels were prepared and scanned to confirm these observations The results were consistent and reproducible Anthophyllite in Talc The anthophyllite used in preparing dilution mixtures of fiber in talc was from the UICC standard asbestos reference mineral collection previously characterized 28 A specimen of this material was continuously scanned by ray diffraction from 3 to 70 20 at min When the peaks on the diffraction pattern were assigned d spacings it was found that the anthophyllite was contaminated by talc chlorite and phlogopite However these intrinsic contaminants do not preclude use of the material as a dilution standard A more serious limiting condition pertains to the similarities between the diffraction patterns of pure anthophyllite and talc see Fig 4 Among the most intense reflections of anthophyllite are the 3.05 ^ obscured by the superposition of the tale 3.12 ^ I = 40 the 4.50 ^ obscured by the 4.53 ^ I = 12 and the 4.56 ^ I = 45 both of tale and the 3.23 ^ obscured by the 3.33 ^ mica contaminant of talc I = 100 Since the background ratio of the most intense reflections of the powder pattern is the most important single factor in determining the minimum detectable amount of a substance the interference between similarly spaced strong reflections of talc and anthophyllite significantly diminishes the possibility of detecting minute amounts of anthophyllite asbestos in talc The 8.26 ^ reflection of anthophyllite with the relative intensity of 55 was selected as the most useful diagnostic reflection for the anthophyllite dilution series Dilution mixtures ranging from 95.0 talc anthophyllite through 99.5 tale anthophyllite were prepared When stepscanned under constant conditions anthophyllite was not detected at concentrations below 2.0 in repeated samples With continuous scanning anthophyllite was not detected at or below the 4.0 dilution level when the 8.26 reflection was used as an index see Fig 4 Preparation and Analysis of Chrysotile Dilution Samples by Electron Microscopy Aliquot portions of various chrysotile dilution levels which had been analyzed by ray diffraction were prepared for transmission electron microscopy by a rubout procedure 32 Standard weights 0.01 mg of each of the dilution standards are dispersed in a nitrocellulose film and mounted on Formvar electron microscope grids The dispersal is accomplished by mounting the sample in a drop of nitrocellulose acetate solution on a microscope slide and grinding it with the edge of a clean watch glass to reduce the sample into submicron particles This procedure breaks apart the fiber bundles of chrysotile already greatly comminuted by triple air milling and sonification into unit fibrils or into small fiber bundles At the same time large aggregates of talc particles are reduced in size and dispersed to allow all asbestos fibers to be seen and counted After dispersing the sample a drop of amyl acetate is placed on a second clean side The two slides are placed in contact and the ground residue and nitrocellulose solution is further dispersed The residue is typically spread over the slide for a length of 5 cm The two slides are then pulled apart leaving two films with the powder uniformly distributed in them The films quickly dry The edges of the slide with attached film are scraped with a scalpel blade then by dipping the slide into water the film can be floated onto the surface of the water Electron microscope grids are placed on top of segments of the film and covered with a strip of filter paper The grid is retrieved by lifting the filter paper out of the water After drying the grids can be picked off the filter paper and mounted in the electron microscope for scanning Typically three grids are prepared for each dilution level of chrysotile and six squares of each grid are scanned at about 10,000x magnification to obtain a number of representative fields for study A large number of fields are photographed and enlarged prints are then made From the photographic enlargements the number of long unit fibrils per field are counted December 1974 105 and the results are tabulated When multiple fibril bundles are encountered the number of unit fibrils in the bundles is estimated by counting the number of visible central capillaries and by judging the optical density of the fiber bundle The electron microscopic fiber counts showa fairly good correlation with levels of chrysotile dilution For example the average number of chrysotile fibrils per field scanned at 7100 magnification was counted at the following dilution levels % chrysotile talc 92 fibrils per field -10 % chrysotile talc 22 fibrils per field - %% 0.5 chrysotile talc 8 fibrils per field -10 0.25 chrysotile talc 6 fibrils per field -10 It is evident that there are considerable numbers of chrysotile fibers present in talc even at very low dilution levels By using the fiber count data for the various dilution levels it is possible to calculate the number of fibrils contained in a unit weight of sample The area of the nitrocellulose film is known as is the magnification factor From these and a measurement of the area of the photographs a conversion factor is calculated Allowing for an error as large as one magnitude the calculations show that there are 2N ^ 108 fibrils of sample the value N being the average number of fibrils per field Thus in a % dilution of chrysotile in talc there would be about 4 ^ 109 fibrils At the lowest level of detection of chrysotile by ray diffraction i.e. 0.25 there would be about a 109 fibrils It is clear that in issuing regulations specifying the absence or absolute limits of asbestos in talc close attention must be paid to the capabilities of the analytical technique used for determining whether or how much asbestos is present ray diffraction can provide positive answers to these questions only at the 0.25 level for chrysotile which has been shown to be a crude and inaccurate measure of the potential contamination and possible hazard involved In addition as much as 2.0 of anthophyllite in tale may not be detected by this method On the other hand electron microscopic analysis can be a sensitive tool for detecting extremely minute amounts of chrysotile and other asbestos minerals in talc Application of Transmission Electron Microscopy Methods Including Selected Area Electron Dif- fraction in Detection of Asbestos in Consumer Talcs Consumer talcs have been prepared and examined by means of transmission electron microscopy Representative sample aliquots were sonically dispersed in filtered water and pipetted onto Formvar mesh copper electron microscope grids After these preparations were dry they were again carbon coated to insure a thermally and electrically stable preparation Samples were scanned at magnification in excess of 20,000 and examined for their fiber content A representative platy and fibrous tale is shown in Figure 6. The asbestos content of talc may be directly estimated utilizing transmission electron microscopy Each fiber type may be identified For example chrysotile asbestos is morphologically unique Its internal capillary fibril dimensions susceptibility to electron beam damage and unique electron diffraction pattern all make the fiber easily recognizable 33 Fibers which are electron and which possess the morphological characteristics of amphiboles were examined by selected area electron diffraction for confirmation We have done this on many particles in numerous samples and are able to differentiate fibrous tale from fibers of asbestos quite easily Fig 7 33 However this method is not sufficiently sensitive to distinguish among the amphiboles Here microchemical characterization is necessary 34 Electron microscopy is an excellent qualitative tool for determining the presence or absence of asbestos fibers in tale Microchemical Analysis by Electron Microprobe Analysis By means of microchemical analysis it is possible to differentiate among the amphibole asbestos fiber types We have examined tale samples obtained from a mill in which anthophyllite and tremolite fibers occurred within the talc These samples were examined on an ARL electron microprobe analyzer equipped with crystal spectometers The instru- 106 Environmental Health Perspectives FIGURE 6. Transmission electron micrographs of A a platy tale and B a fibrous tale The platy talcs tend to be made up of a mixture of formed polygonal and ragged edged sheets Fibers visible are talc fibers The fibers in B are made up of tremolite anthophyllite and tale Fibrous components and non- fibrous objects are common Magnification for A and B as marked ment and technique elsewhere 30 31 have been described Tremolite may be easily differentiated from fibrous talc on the basis of its high calcium content and Mg ratio but anthophyllite depending on its iron content may not be Fig 8 These latter amphiboles may be differentiated from fibrous tale only on the basis of electron diffraction characteristics Also where fiber ends are visible it is possible to differentiate tale from anthophyllite morphologically Tale fibers tend to have prism truncation whereas anthophyllite does not Fig 7 Microchemical FIGURE 7. Selected area electron diffraction patterns obtained on A a talc plate and marked TF in B a talc fiber Talc fibers are not confused with amphiboles They are often curvilinear possess irregular diffraction contrast contours as do tale plates tend towards prismatic truncations and have identical diffraction patterns as compared with plates techniques may be of limited use because of the time involved in analysis Samples with a large number of fibers may be subjected to microchemical analysis to define the types of particles present This requires the definition of standards and the analyses of several hundred representative fibers in the sample The technique is excellent for characterization but is not recommended as a routine analytical method 34 Summary and Conclusions Talc because of its composition conditions of formation and geological occurrence is frequently contaminated with asbestos fibers The presence of fibers may be determined by a number of instrumental techniques Some in- December 1974 107 Co FIGURE 8. Electron microprobe analyses of 95 particles observed in a fibrous talc from New York State A represent scanning micrographs obtained monitoring backscattered electrons of a fibrous tale dust A an amphibole fiber in the dust B analyzed as tremolite and C a tale grain The complex intergrowth of many phases invariably yields an analysis outside of the ideal compositional fields D talc anthophyllite tremolite emission fields in the system Mg These analyses are scattered about these fields Chemical analysis based on elemental emission termed analysis by Rubin and Maggiore 34 show the presence of talc tremolite anthophyllite quartz feldspar and carbonate phases Differentiation between amphibole minerals is easily achieved talc and anthophyllite fibers generally require structural characterization by selected area electron diffraction as well struments provide direct visualization of the fibrous objects Although light microscopy and electron microscopy are excellent tools for qualitative analysis each has distinct disadvantages Use of light microscopy is restricted to analysis of objects larger than 1 ...mElectron microscopy requires extensive sample preparation and instrument time Both techniques require homogeneous sampling to achieve quan- titation or even estimates of fiber content Uni- que characterization of amphibole fibers by transmission electron microscopy anthophyllite and tremolite versus fibrous talc requires structural analysis selected area elec- tron diffraction characterization and microchemical Quantitative analysis for fiber may be achieved by ray diffraction techniques employing scanning modes of operation on selected characteristic reflections Preparation by slurry filtration yields cakes which provide homogeneous samples for analysis Samples thus prepared yield reproducible ray counting results Each fiber type has its own level of sensitivity related to matrix and ray sorbtion effects Anthophyllite may be detected at levels of 2.0 chrysotile 0.25 and tremolite at 108 Environmental Health Perspectives 0.10 by weight in a tale matrix Quantitative analysis of mineral systems more complex than two phases in composition may be compared with binary standards with limitations We recommend the use of both ray diffrac- tion analysis by scan mode of operation and transmissin microscopy with selected area electron diffraction for analysis of consumer talcs for their asbestos fiber content Acknowledgement The authors wish to acknowledge support under a NIEHS Center Grant ES 00928. One of us AML wishes to acknowledge support under a NIEHS Career Scientist Award ES 44812 REFERENCES 1. Ford W. E. Dana's Textbook of Mineralogy Wiley New York 1957 P. 851 2. Deer W. A. Howie R. A. and Zussman J. RockForming Minerals The Sheet Silicates Wiley New York 1962 3. Bowen N. L. and Tuttle O. F. The system MgOSiO2 Bull Geol Soc Amer 60 439 1949 4. Yoder H. S. The A1203 system and related metamorphic facies Amer J. Sci Bowen Memorial Vol 569 1952 5. Ross M. Smith W. L. and Ashton W. Triclinic tale and associated amphiboles from Gouverneur Mining District N. Y. Am Mineralogist 53 751 1968 6. Wells J. R. Soapstone and pyrophyllite In U.S. Bureau of Mines Bull 630 Mineral Facts and Problems U.S. Government Printing Office Washington D.C. 1965 p 919 7. Schulz R. Z. and Williams C. R. Commercial talc animal and mineral studies J. Ind Hyg 24:75 1942 8. Kleinfeld M. Messite J. and Langer A. M. 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Detection and identification of asbestos by microscopical dispersion staining Environ Health Perspect 9 57 1974 27. Bragg R. H. Quantitative analysis by powder diffraction In Handbook of Rays McGraw New York 1967 28. Timbrell V. Characteristics of the International Union Against Cancer standard reference samples of asbestos In Pneumoconiosis Proc Int Conf Johnannesburg 1969 H. A. Shapiro ed Oxford Univ Press London 1970 pp 28 29. Klug H. P. and Alexander L. E. Ray Diffraction Procedures Wiley New York 1954 30. Cullity B. D. Elements of Ray Diffraction AddisonWesley Reading Mass 1956 31. Brindley G. W. and Kurtossy S. S. Quantitative determination of kaolinite by Ray diffraction Am Mineralogist 46 1205 1961 32. Leineweber J. P. A method for determination of the fiber content of water Manville Research and Engineering Center Rept No. E404-37 1968 33. Langer A. M. Mackler A. D. and Pooley F. D. Electron microscopical investigation of asbestos fibers Environ Health Perspect 9 63 1974 34. Rubin I. B. and Maggiore C. J. Elemental analysis of asbestos fibers by means of electron techniques Environ Health Perspect 9 81 1974 December 1974 109