Document g65Yry5KwXqDmyER7GpZLJM9

FILE NAME Talc TALC DATE 1990 DOC TALC200 DOCUMENT DESCRIPTION Journal Article - Asbestos Standard TEM Procedure for Identification and Quantitation of Asbestiform Minerals in Talc a The Tenth In a recent 1 piece about the test diatom Nitzschia firthii Fuge I quoted Spitta's comments 2 which includ- ed the meter in reference to the wavelength of light 4700 meters recommended to best resolve the lines striae on the diatom valve face I feel an explanation of this term as used by Spitta is owed to readers of this column In a footnote on p 267 of his text I find It should be mentioned here perhaps although hardly in logical sequence that even the or micron is not small enough a unit for the physicist when dealing with the measurement of the wavelengths of light In this case the German savants employ what is called the double mu written which is the thou- sandth part of the micron but the English scientist adopts a smaller unit still called the meter which is the ten thousandth part of the micron the raison d'^'treof the term being that 10 10 at the tenth power go to a meter From this then we realize that the meter is equivalent to the Angstrom Unit named after A.J. Angstr^m1814-74 a Swedish physicist and defined as thousandth of a micron However in this age of enlightenment after great strides in clarifying scientific terminology we have dropped the micron in favor of the micrometer and the millimicron in favor of the nanometer and so since the Angstrom is one ten thousandth of a micron micrometer Spitta was recommending light of 470 nanometers Got that References McLaughlin 1. R.B. Nitzschia firthii Fuge A Test Diatom The Microscope 1990 38 2. Spitta Edmund J. Microscopy The Construction Theory and Use of the Microscope E.P. Dutton and Company New York 1920 JNL61_076 456 MICROSCOPE JNL61_07 chrysotile.amosite crocidolite anthophyllite actinolite tile amosite crocidolite anthophyllite tremolitechrysotile tremolite crocidolite anthophylite ASBESTOS ASBESTOS ASBESTOS crocidolinth ASBETOS ASBESTOS croci- ASBESTOS dolite ASBESTOS ASBETOS ASBESTOS ASBESTOS ASBESTOS crocido- lite anthophyllite chrysotile anthophyllitetremo- lite chrysotile amosite anthophyllite A Standard TEM Procedure for Identification and Quantitation of Asbestiform Minerals in Talc Thomas Kremer McCrone Associates and James R. Millette Ph.D. Millette Vander Wood Associates Inc / Keywords Asbestiform asbestos MSHA OSHA talc TEM amphiboles mineral fibers microscopy electron microscopy ABSTRACT A standard method for the preparation of powdered talc for transmission electron microscope TEM analysis has been developed to identify and quantify small quantities of asbestos and related minerals The method utilizes an aqueous suspen- sion treated with methyl cellulose Particles are mounted by transferring a drop of the water suspension to a TEM grid bearing a formvar film which has been coated with evaporated carbon Once dry two grids per sample are examined in the TEM at magnifications of 5,000X and 20,000X for elongate and 850 Pasquinelli Drive Westmont IL 60559 5500 Oakbrook Pkwy Suite 200 Norcross GA 30093 457 fibrous particles Morphology crystal structure and elemental composition are used to identify and characterize particles of interest Calculations are included to determine a detection limit and determine concentration in weight percent INTRODUCTION The regulatory definition of asbestos was established in 1972 when the National Institute of Occupational Safety and Health NIOSH published its definitions and analysis methods for asbestos 1 Under their method asbestos was defined as any fiber of chrysotile crocidolite amosite anthophyllite tremolite or actinolite What has come to be known as a federal fiber was defined as a particle with a length to width aspect ratio of at least 3 and a length greater than 5 micrometers m1 Although NIOSH has set forth phase contrast microscopy PCM as the analytical tool for regulating airborne asbestos it has acknowledged the need for and has used analytical electron microscopy AEM to identify asbestos in air samples and bulk talc samples 2,3 Both the Occupational Safety and Health Administration OSHA and the Mine Safety and Health Administration MSHA refer to NIOSH methods As regulatory agencies OSHA and MSHA are responsible for monitoring the safety of workers in the work and mine environments respectively which includes setting limits on the levels of hazardous materials to which a worker may be exposed The primary route of asbestos exposure is inhalation therefore air concentration limits were established 4 A primary source of airborne dust is fine particle bulk materials Consequently manufacturers have been concerned with the potential presence of these minerals in their products in any measurable quantity In February 1990 OSHA promulgated a Hazard Communication Standard HCS 5 The HCS requires producers to label as a carcinogen bulk materials and bulk minerals and products which contain 0.1 or more of asbestos and pending supplemental rulemaking to be completed November 1990 asbestiform anthophyllite tremolite and actinolite To meet this standard a more sensitive method to detect asbestos is needed Such low levels are not quantifiable by polarized light microscopy and the morphology of fibers is not discernible by ray diffractometry Transmission JNL61_017 458 MICROSCOPE JNL61_07 THOMAS KREMER et al electron microscopy is capable of detecting these low levels and has been recognized by both government and industry for sev- eral years 3,6 Given the NIOSH definition of asbestos and the low levels to which it must be detected the need arose for quantitative TEM analysis of powdered talc To meet this need McCrone Environmental Services developed the following method which , has been in use since 1985 Standard Operating Procedure Analysis of Powdered Talc for Asbestiform Minerals by Transmission Electron Microscopy 1. Scope and Purpose This method is applicable to the identification and quantitation of small typically 1-20 micrometer elongate minerals in powdered talc and was designed for chrysotile and the elongate forms of tremolite actinolite and anthophyllite Samples may be previously screened by light microscopy or ray diffraction . techniques 2. Principle of Method The combined techniques of transmission electron microscopy TEM selected area electron diffraction SAED and energy dis- persive ray spectrometry EDS permit the detection of asbestiform minerals based on morphological characteristics followed by a definitive mineralogical identification of each fiber These techniques are currently the best analytical tools for the determination of fine asbestos minerals in talc matrix 3. Interferences Interferences caused by other fibrous particles must be distin- particle guished from positively identifiable asbestos Large or particle aggregates may obscure fibers Positively identified asbestos fibers include enrolled talc ribbon talc Figures 1A and B antigorite Figures 2A and C talc fragments Figures 3A and B silica and oxide fibers Organic additives such as perfumes may crystallize as fibers or shaped crystals in 459 THOMAS KREMER et al Figure 1a Talc platelets and attached ribbon Figure 2a Antigorite rectangular lath with its superimposed electron diffraction pattern Figure 1b SAED pattern of a talc ribbon with its 001 face oriented approximately parallel with the electron beam JN L61_0 0178 JNL61_0178 460 MICROSCOPE JNL61_0 78 Figure 2b SAED pattern with a diagnostic 35 to 40 A spacing in the crystallographic direction 461 Cursort 1.250kV = 63 57531-781 BSS 57531-781 1918 THOMAS KREMER et al Cursor 1.240k@V = 489 SK 1.778 _ Figure 2c The elemental composition determined by EDXRA is characteristic ofa serpentine mineral pattern of talc showing the typical 001 zone axis oriented Figure phylosilcate SAED of a phyllosilicate mineral with the 001 face oriented perpendicular perpendicular to the electron beam JN L61_0 0179 JNL61_0179 462 MICROSCOPE JNL61_0 79JNJNL61_000179 i=l rR _ i iw at Figure 3b EDXRA spectrum characteristic of talc finished cosmetic products In the absence of positive identifica- tion all other fibers must be classified as unidentified 4. Instrumental Conditions Instrumental are examined in the TEM at an acceler- The talc specimen grids of 5,000X and ating voltage of 120 kV and at magnifications 20,000X 5. Sensitivity This method can detect a single fiber as small as 1 micrometer ...mlong by 0.075 ...mwide in the entire TEM field which results in a theoretical detection limit of 105 weight percent Such fibers usually can be identified readily by SAED and EDS The mass of a fiber with the above dimensions is about 1.1 x 10-14 g for chrysotile and about 1.9 ^ 10-14 g for amphiboles 6. Limit of Quantifiable Detection quantifiable The detection of five or more asbestiform minerals of one vari- level of detection ety in an analysis constitutes a When no asbestiform minerals are detected a representative fiber size is used to calculate a detection limit A representative fiber size is 3 mlong by 0.2 mwide by 0.06 mthick which is to considerably larger than the smallest fiber than can be detected see Section 5 Sensitivity but it is more typical of small asbestos fibers that are detected in talc analyses The mass of five such fibers is calculated as follows 3 mx 0.2 mx 0.06 m= 0.036 mper fiber x 3.3 x 10-12 um= 1.2 ^ 10-13 g per fiber x 5 fibers = 6 x 10-13 grams The limit of quantifiable detection for most talc analyses is approximately 6 x 104 weight percent The theoretical and quantifiable detection limits assume homogeneity of the material being sampled 7. Quality Assurance Blank suspensions are routinely prepared and tested in order to monitor potential residual contamination from the sample jars Blank carbon grids are routinely tested to monitor the ambient fiber count If greater than 4 fibers per grid are present the jars are cleaned or new carbon grids are prepared respective of the test For each analysis one grid opening is examined by another analyst as a quality control check 8. Background Correction As of the time of this writing background correction has not been necessary Blank contamination is very rare and corrective steps are taken before the testing of material proceeds 9. Preparation and Analysis Time Preparation time per sample including preparation of related materials is one hour Analysis search time per sample is a maximum of two hours 10. Apparatus A. Analytical balance with 0.0001 gram sensitivity B. Weighing boats C. Narrow spatula JNL61_0180 464 MICROSCOPE JNL61_08 THOMAS KREMER et al D. Wide mouth polyethylene jars 125 mL E. Mild ultrasonic bath 50-60 watts F. Micropipette 5-10 Lrange with disposable tips G. Standard 3 mm diameter 200 mesh copper TEM grids cov- ered with carbon formvar film H. Transmission electron microscope TEM with an 80-120 kV accelerating voltage and energy dispersive ray analyzer 11. Reagents A. Methyl cellulose powder USP 4000 cps - Fisher Certified Reagent 352 or equivalent B. Water deionized particle free 0.2 ...mfiltered C. Methyl cellulose solution 0.002 wt 20 ppm Dissolve 20 0.5 mg of methyl cellulose in 500 mL of deionized particle- free water to make a 0.004 stock solution Dilute 1 to make a working solution aid maintain- Note Methyl cellulose acts as a wetting agent to aid in maintain- ing a uniform particle distribution as the sample dries 12. Sample Preparation 12-1 Transfer 30 to 50 mg of talc powder to a clean 125 mL polyethylene jar 12-2 Add 80 mL of 20 ppm methyl cellulose solution cap and shake vigorously for one minute 12-3 After shaking loosen cap and ultrasonicate for 10 minutes in order to disperse the finer particles Then shake again for one minute to produce a uniform suspension 12-4 Immediately after shaking uncap and remove 9.2 ...Lby micropipette 12-5 Transfer 9 ...Ldrop to a carbon film covered TEM grid Grid is first lightly anchored by 2 parallel strips of double tape mountedabout 2.5 mm apart on a clean glass microscope slide Repeat to make two sample grids per talc sample Note Do not expel the remaining 0.2 ...Lsuspension from the 465 THOMAS KREMER et al micropipette tip It tends to sputter and frequently destroys the stability of the sample drop the type of amphibole 14. Calculation of Results 12-6 Transfer slide with grids to a desiccator Drying time is 23 hours Do not leave the grids on the slide for more than one day as the double tape may adhere too tightly Note The water ratio may need to be varied for some sam- ples Preparation of talc samples with significantly finer or coarser particles results in large differences in particle coverage on the TEM grid 13. TEM Analysis 13-1 Definition of fiber an elongated particle with parallel sides and an aspect ratio Wh3en this definition is employed fibers which fit the OSHA 4 EPA 7 or client's definition can be selectively extracted from the total fiber data for each analy- sis 13-2 Scan sample at 120-150X magnification to check for even dispersion of particles and to locate grid squares with optimum particle density Optimum particle density is particle coverage over 15-35 of the field of view 14-1 where Mass of chrysotile fibers M M = xd r = fiber radius 1 = fiber length d = density of chrysotile = 2.55 x 10-12 ...m = 3.14159 14-1 Mass of asbestiform amphibole particles M 1xwx = length w = width th = thickness = 0.3 width approximation d = density of amphiboles = 3.3 x 10-12 ...m 14-2 Mass of talc deposited on each TEM grid step 12-5 M = Tx Tx H T = amount of talc sampled step 12-1 V = volume of aliquot transferred to TEM grid step 12-5 H = volume of methyl cellulose solution step 12-2 14-2 Total estimated talc mass examined M M = M x Nx Nx A 13-3 Scan three grid squares on each grid at 20,000X magnification and seven grid squares on each grid at 5,000X for asbesti- N = number of grid squares examined A = area of a single TEM grid square form minerals Each asbestiform mineral is recorded as to type chrysotile tremolite anthophyllite etc. structure bundle A = area of an entire TEM grid effective area over which a 9 ...Ldrop of suspension dries clump fiber and dimensions length x width 14-3 Weight percent 13-4 Questionable fibers are examined first by SAED The chrysotile SAED pattern is unique and diagnostic Amphibole sum total of M or M x 100 M SAED patterns are variable but usually characteristic 15. Calculation of a Detection Limit Additional analysis and measurement of amphibole SAED pat- terns are done if warranted 15-1 M = A minimum quantifiable mass of asbestos fibers based on the detection of 5 fibers 13-5 Ten percent of chrysotile fibers are checked by EDS for further confirmation If the SAED pattern is not clearly diagnos- approximately 6 x 10-13 grams from Section 6 tic or if it is consistent with an amphibole SAED pattern then it is examined by EDS to confirm the identification or to identify 15-2 Detection Weight Percent = dl x 100 M JNL61_081 466 MICROSCOPE 467 JNL61_08 ins eo =~ ee REFERENCES 1. National Institute for Occupational Safety and Health NIOSH Membrane Filter Method for Evaluating Airborne Asbestos Fibers by N.A. Leidel S.G. Bayer R.D. Zumwalde and K.A. Busch Technical Report No. 79-127 Cincinnati OH 1979 2. National Institute of Occupational Safety and Health Method 7402 NIOSH Manual of Analytical Methods Carter J.W. Baron P.A. and Taylor D.G. pp 7402-1-7402-7 1986 3. Dement J.M. Asbestiform Minerals in Industrial Talcs Commercial Definitions versus Industrial Hygiene Reality Proceedings of the Workshop on Asbestos Definitions and Measurement Methods National Bureau of Standards Special Publication 506 Washington D.C Government Printing Office pp 313-323 1978 4. Occupational Safety and Health Administration 29 CFR Part 1910 Occupational Safety and Health Standard Federal Register Special Publication Washington D.C Government Printing Office 1989 5. Occupational Safety and Health Administration 29 CFR Parts 1910 and 1926 Occupational Exposure to Asbestos Tremolite Anthophyllite and Actinolite Notice of Proposed Rulemaking Federal Register pp 4939 ff Vol 55 No. 29 12 February 1990 6. Stanley H.D. The Detection and Identification as Asbestos and Asbestiform Minerals in Talc Proceedings of the Workshop on Asbestos Definitions and Measurement Methods National Bureau of Standards Special Publication 506 Washington D.C Government Printing Office pp 325-337 1978 7. Environmental Protection Agency Containing Materials in Schools Final Rule and Notice Federal Register Vol 52 No. 210 30 October 1987 JN L61_0 0182 JNL61_0182 468 JNL61_082 MICROSCOPE > it {{ Book Reviews GOD BLESS THE MICROSCOPE A History of the Royal Microscopical Society over 150 years Gerald L'e Turner published by the Society 116 pages 48 figures On 3 September 1839 17 microscopists met at No. 50 Wellclose Square at the invitation of Edwin Quekett the owner They met to consider forming a society for the promotion of microscopical investigation and for the introduction and improvement of the microscope as a scientific instrument The timing was right because during that decade Joseph Jackson Lister had published his classic paper on the achromatization of microscope lenses Only then was the compound microscope able to perform the simple Leeuwenhoek microscope Note Brian Ford tells us that Antony only followed the directions of Hooke a Britisher who had earlier produced Leeuwenhoek micro- scopes In any case the Society was formed by Quekett and his guests among whom were Joseph Jackson Lister James S. Bowerbank and Nathaniel Ward These men had met informally over the previous several years and this culminated in the decision taken on 3 September 1839 to form The Microscopical Society of London Philologists will be interested to learn that Joseph B. Read one of the 17 advised the use of microscopical rather than microscopic to prevent the possibility of ourselves being mistaken for microscopic objects Dr. Turner's book covers little microscopical science but there is much biographical data and a complete and very readable account of the history of the after 1867 Royal Microscopical Society It is a great success story with many trials and tribu- lations all overcome with renewed and enhanced status The book is well written well illustrated and should be required reading for microscopists Walter C. McCrone