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f DETECTION OF ASBESTIFORM AMPHIBOLE MINERALS IN COSMETIC GRADE TALC Introduction The method which has been adopted for the detection of amphi bole minerals in cosmetic talc is the generally accepted method of x-ray diffraction. Methods which appear in the literature for the detection of fibrous amphibole, such as, transmission electron microscopy with selected area diffraction-*- and electron xnicroprobe^, have also been considered since they are capable of a lower level of detection than by x-ray diffraction. How ever, they have not been adopted since they suffer from the drawbacks, that the amount of material under examination is quite small (less than a microgram) and the time for analysis, expertise required, and expense of equipment eliminates them as routine methods. Enrichment or concentration techniques using flotation cells have been tried as a means of improving the detection level; however, all efforts so far have been unsuccessful. Principle The x-ray diffraction method is based upon the principle that when a crystalline material is placed in an x-ray beam, a portion of the x-rays are diffracted by each set -of atomic planes with in the crystal. The diffracted rays strike a scintillation counter as the sample is scanned through a prescribed angle with the resulting dev< of peaks corresponding to each inter- planar distance (d). A peak with d value in the range of.c S.04 to 8.85A0 for a sample talc is strong evidence for the presence of amphibole in that talc. The level of detection of amphibole by this method is 0.5% and above. The variability of detection is caused by such factors as age and manufacturer of x-ray diffractometers, sample homogeneity, specific amphibole mineral present, morphology o amphibole, particle size, preferred orientation, etc. For these reasons the 3evel of detection should be reported for levels above 0 .5%, since below this level the data has been found to be not reproducible. If a peak is found in the d range for amphibole, described above, then the sample must be put through the following confirming scheme: (+) (-) X-ray Diffractometry----- y Optical Microscopy------- ^ Stop (Acid and Leach) Dispers ion-S taining (ainuhibole ` X. absent) sy Stop (amphibole absent) Color v/-(+) Fibrous Morphology \` (+) -Cl.)__ ^ s t o p (a.sbestifo::n atup_ __J ludo "jr . Stop absent (asbesti form ampliioo1e present) Part I Detection of Amphibole Minerals by X-ray Diffractometry Apparatus 1. X-ray diffractometer, employing nickel-filtered copper K-alpha radiation, horizontal or vertical goniometer with variable scan speed capability, suitable talc pellet sample holder, variable speed recorder, elec tronic panel including ratemeter and variable atten uation and time constant settings. 2. Hydraulic press, capable of attaining a pressure of 15,000-24,000 lb. calculated on a 3" ram. 3. Mortar and pestle or grinding mill (Note 1). o ) M 4. , or equivalent blender. o>^ 5. [*, or equivalent mechanical mixer. .6 Sieve, 325-mesh. 7. Optical microscope. (Note 2) . 8 . 1-1/4" pellet press. Reagents 1. Standard talc sample, containing no detectable amphibole minerals. 2. Standard tremolite sample, at least 95% pure. 3. Denatured ethanol. 4. Boric acid. Procedure The procedure consists of slow-scanning, under previously deter mined conditions, a compressed pellet of the sample talc in the 11.0-10.O20(8.85-8.04A) region for the presence of an amphibole peak. There are times when it is difficult to discriminate a possible peak for amphibole over the background noise level. ^Registered Trademark Should the presence of a small amphibole peak above the background "noise" be in question, it will be necessary to statistically evaluate the scan. A timer/scaler is required on the electronic panel of the x-ray diffractometer. In order for a peak to be statistically signifi cant, the peak intensity must equal or exceed three standard deviations (3iS) above the average background intensity (N): N + 3G = minimum peak intensity, where N = average background count, and & = t J T Procedure 1. First, determine the region of the scan in question: in the above scan a peak appears to be present in the 10.40 - 10.60 20 region. 2. Slow scan with cumulative pulse counting through the peak region three separate times and average the number of counts. 3. Next, a background count is determined by scanning a region equal to 1/2 of the 20 region covered by the peak, immediately before and after the peak. The counting time for each of these background regions will equal 1/2 the total counting time used for the peak. Each background region is counted three times. Each region is then averaged and the two averages are added to obtain the background count (N). Example: In the above diagram, Peak Background Region A Region B Peak 10.40-10.60 26 time secs. counts 120 60,332 120 59,870 120 60,105 Average 60,102 Region (20) ro 40-10.60" Time (sec.) ---- I2 10.30-10.40 60 10.60-10.70 60 Background Region A Region B 10.30-10.40 20 10.60-10.70 26 time secs. counts time secs. counts 60 28,784 60 28,506 60 28,943 60 28,368 60 28,634 60 28,204 28,787 28,359 N = 28,737 + 28,359 = 57,146 & =27746 = 239 3 Q = 717 N+ 36 = 57,146 + 717 = 57,863 The actual number of counts obtained for the integrated peak intensity was 60,102; therefore, the "suspect" peak is statistically present in the scan. 1 Standard Preparation Optimal instrument conditions must first be determined with the use of tremolite standards - 1.0%, 0.75%, 0.5% tremolite by weight, prepared in a standard talc which is free of interfering peaks in the 11.O-1O.O20 region. The tremolite standards are prepared in the following manner: a. Weigh out appropriate amounts of standard talc and tremolite both of which have been ground to pass a 325-mesh sieve. Transfer to a Waring Blendor*. Add 100 ml. of ethanol to the blender and blend at low speed for 5 minutes. b. Carefully transfer, with repeated ethanol washings, the contents of the blender into a large beaker. Evaporate the ethanol on a steam bath. c. Shak^thesample in a plastic vial for 5 minutes on a to remove clumps and caked sample resulting trom the evaporation of ethanol. d. Determine by microscopy the homogeniety of the pre pared standard previous to the x-ray diffraction analysis. e. Press the homogeneous standard into a 1-1/4" pellet with a backing of boric acid. 2 (jl0 .2) gram of standard is transferred to the die-holder and evenly distributed on a polished, scratch-free die. Distri bute 4(+ 0.2) grams of boric acid evenly on the talc layer. Press the mixture into a pellet under condi tions suitable for obtaining a smooth planar surface (for example, a pressure of 15,000-24,000 lb. calcu lated on a 3" ram was found to produce suitable pellets) . The resulting pellet must have a talc face which is free of flaws; if not, the pellet must be discarded. (Note 3). Two acceptable pellets are prepared from each standard. ^Registered Trademark 2 Sample Preparation Prepare two pellets from each sample in the manner described for the standard pellets (1., Step e.). Make a qualitative scan from 4-502Q on one of these pellets to ascertain the presence of amphibole above the 27o level or the presence of mineral impurities having interfering peaks in the 11.0-10.028(8.858.04A) region of the scan. The presence of such interference will eliminate use of the x-ray dif fraction method for the sample, and one will have to proceed directly to the microscopical procedure. 3 Instrumentation Instrumental variables are optimized on the 1% standard. Lower standards are then analyzed under the optimun con ditions to determine the lower level of detection. Of major importance in obtaining maximum instrument sensi tivity are a slow diffractometer speed combined with compatible recorder speed, and high attenuation combined with a statistically acceptable time constant on the ratemeter. Under appropriate instrumental conditions the peak obtained for the 0 .5% standard' should be detect able above background noise as per the scan on the fol lowing page. Typical instrumental conditions employed for the Siemens Diffractometer (Model No. M386-X-A4), and Counter and Recorder Unit (Type T) are: Radiation : Divergence slit: Goniometer speed: Recorder speed: Attenuation : Time constant: Cu with K-^ filter at 40KV and 24 ma 1 Receiving slit: 0.2 mm 1/1020/minute 300 mm/hour 1 x 10^ impulses/second T (s) = 4 Statistical error of 1.1% under these conditions 100 - 90~ 80 706050- 0.5 % Tremolite Intensity 40 ~ 30- 20 - 10- 0 - * i 0 I 8 B f ff f I 9.6 10.0 10.2 10.4 10.6 10.8 11.0 .11.4 20 .CTFA Method Rise Time = 0.18 Attenuator = 20 4 - X-Ray Diffraction Scans The standard or sample pellet is placed in a suitable holder and slowly scanned between 11.0 and 1O.O20. The pellet is then rotated 90 with respect to its original position in the goniometer and rescanned between 11.0 and 10.02G since pellet orientation may affect peak intensity. The presence of a reproducible peak (or peaks) is due to the presence of amphibole minerals; the absence of peaks in this region indicares the absence of amphibole in the sample, within the limit of detection of this technique. Part II Detection of Asbestiform Amphibole Minerals by Optical Microscopy and Dispersion-Staining Apparatus 1. Polarizing microscope. Best results will be obtained if the instrument includes the following: O K h) a. Individually centering objectives lens c. High-intensity light source d. Centering condenser/substage 2. Dispersion-staining device. (Note 4) 3. Vacuum filtration equipment, including either a porce lain cone with glass fiber filter mat or a porous glass bottom cup.- Reagents 1. Hydrochloric acid, 10% v/v. D immersion liquid Series HD, ^ 5 =. 1.605 (Note 5) Acid Treatment Because of the interference caused by some carbonates (e.g. calcite) in the detection of asbestiform amphiboles in talc by optical microscopy/dispersion-staining, it is necessary to first remove these carbonates by a simple acid leaching procedure: CTFA Method Weigh out 2 g . of the talc into a 100 ml. beaker. Add 25 ml. of 10% v/v Hci slowly (to prevent excessive evolution of gas if carbonates are present) and heat, with occasional stirring on a steam bath for 30 minutes. 2. Filter with vacuum filtration equipment, and wash several times with hot water. Dry the talc. Optical Microscopy and Dispersion-Staining 1. Carefully disperse 0.2 mg. of talc in one drop of Cargille HD liquid n~c = 1.605 and cover with a clean cover slip. 2. Examine the sample in the dispersion-staining central stop mode. The substage diaphragm should be almost completely closed, the field diaphragm may be parti ally closed to enhance color contrast, and the polarizer should be in position. 3. Tremolite, actinolite and presumably other amphibole minerals, under these conditions, will show the following dispersion-staining colors: yellow changing to blue with rotation of the sample rela tive to the polarizer or yellow changing to orange with rotation. The variation of the color change is due to the fact that the tremolite may lie in one of two positions relative to its principal optical orientation. 4. In order for an amphibole mineral to be considered asbestiform or fibrous it must meet the following OSEA definition. (Reference 4) a. Particles must appear to be fibrous rather than as crystals or slivers. b. The maximum diameter of a fiber to be counted is 3 microns. c. The maximum length of a fiber to be counted is 30 microns. d. The length to width ratio must be 5 or more to 1, that is, 5 times or more longer than wide. e. The separate or individual fibers must contain fibrils or the "bundle of sticks" effect, unless they are at a non-divisible stage. A fibril cannot be subdivided and would be counted, if it meets the other criteria. The length to width ratio of 5 or more to 1 is not meant to imply that other particles are not hazardous. 5. It is imperative that both dispersion-staining color and fibrous morphology criteria be satisfied before identifying a particle as asbestiform amphibole, since other substances may show colors similar to those described. Notes 1. Talcs to be analyzed and the tremolite used to prepare standard samples must be -325 mesh (maximum particle size of 44 microns). The Tekmar Analytical Mill (Model A-10) is recommended. It is available from: Tekmar Company P. 0. Box 37202 Cincinnati, Ohio 45222 2. It is important that the homogeneity of the prepared talc-tremolite standard samples be verified by optical microscopy. 3. This requirement is critical since excessive surface scatter will cause abnormally high background counts. 4. The only commercially available dispersion-staining device is sold by: Walter C. McCrone Associates, Inc. 2820 South Michigan Avenue Chicago, Illinois 60616 5. Available from: R. P. Cargille Laboratories, Inc. Cedar Grove, N. J. 07009 - or from laboratory suppliers. References 1. Rohl, A . N . Langer,A.M., Environmental Health Perspectives 9, 95 (1974) 2. Rubin, I.B.Maggiore, C.J., Environmental Health Perspectives _9, 81 (1974) 3. L.S. Birks, X-Ray Spectrochemical Analysis, page 54-55 Interscience Publishers (1959) 4. "Tremolite and Talc". U.S. Department.of Labor, Occupational Safety and Health Administration, Field Information Memorandum #74-92, November 21, 1974.