Asbestos Fibers and Other Elongate Mineral Particles: State of the ...

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ased on counts made by the current PCM method, counts made with improved optical microscope resolution capabilities would not be directly comparable to current occupational exposure limits for airborne asbestos fibers. Additionally, the findings that asbestos fibers thinner than 0.1 µm are most associated with mesothelioma and that optical microscopes cannot resolve fibers
new RIB graticule on the precision of measuring fiber dimensions; and • to determine the interlaboratory variation of the proposed method for determining particle identities by observing morphological features of individual particles. Anticipated outcomes of these ongoing research projects include a measure of method precision, which will help to determine whether the method meets the requirements of regulatory and other agencies. Although EM may currently not be suitable for routine analysis of samples of airborne EMPs, EM techniques used to characterize and identify minerals (e.g., differentiating between asbestos fibers and other EMPs) should be further investigated and evaluated to determine whether results are reproducible by multiple microscopists and laboratories. 3.6.4 Develop Analytical Methods to Assess Durability of EMPs Although research has been conducted to determine the ability of biological assays to evaluate the biopersistence of EMPs in the lung, there is a need to consider how the assessment of EMP durability might be incorporated into the evaluation of air samples containing a heterogeneous mix of EMPs. Research with several types of glass fibers and some other SVFs indicate that they dissolve in media at different rates depending on the pH and that they dissolve more rapidly than chrysotile and amphibole asbestos fibers [Leineweber 1984]. Chrysotile fibers have been shown to dissolve at a rate that varies not only with the strength of the acid, but also with the type of acid. Amphibole asbestos fibers have been shown to be more resistant to dissolution than chrysotile fibers. Research suggests that the rate of dissolution in the lungs for most NIOSH CIB 62 • Asbestos EMPs appears to be strongly dependent on their chemical composition, surface characteristics, and dimension. The selective dissolution of EMPs might be a useful approach for eliminating specific types of EMPs or other particles collected on air samples prior to analysis (e.g., microscopic counting). The removal of interfering EMPs prior to counting could potentially eliminate the need for additional analysis to identify EMPs on the sample. Selective dissolution of samples to remove interferences is well established in NIOSH practice for other analytes. NIOSH Method 5040 for diesel exhaust has an option for using acidification of the filter sample with hydrochloric acid to remove carbonate interference [NIOSH 2003a]. Silicate interferences for quartz by infrared spectroscopic detection are removed by phosphoric acid digestion in NIOSH Method 7603 [NIOSH 2003b]. Although selective dissolution might be accomplished for some EMPs, research will be necessary to develop and characterize a procedure that would correlate residual EMP counts to the results of toxicity studies. 3.6.5 Develop and Validate Sizeselective Sampling Methods for EMPs For measuring airborne concentrations of nonelongate particles in the workplace, conventions have been developed for sampling the aerosol fractions that penetrate to certain regions of the respiratory tract upon inhalation: the inhalable fraction of particulate that enters into the nose or the mouth; the thoracic fraction that penetrates into the thorax (i.e., beyond the larynx); and the respirable fraction that reaches the alveoli of the lung. The thoracic convention is recognized by NIOSH and other organizations that recommend exposure limits, and NIOSH has 93
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CURRENT INTELLIGENCE BULLETIN 62 As
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CURRENT INTELLIGENCE BULLETIN 62 As
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Foreword Asbestos has been a highly
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Executive Summary In the 1970s, NIO
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NIOSH recognizes that its 1990 desc
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of exposure to various types of EMP
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xii 2.9.3 Biopersistence and other
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xiv List of Figures Figure 1. U.S.
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xvi MAPK mitogen-activated protein
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xviii Brooke Mossman, PhD Universit
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controlled, even when exhaustive lo
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2 Overview of Current Issues 2.1 Ba
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juxtaposition or matrixed together,
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A further source of confusion comes
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Figure 2. Asbestos: Annual geometri
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Figure 3. Number of asbestosis deat
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at home by playing in areas where a
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physician from an occupational and
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of airborne asbestos fibers was fir
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which the deposits have been report
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with the most pronounced excess of
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A limitation of the epidemiological
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CI = 1.8-6.7) was noted in the earl
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exposure to commercial asbestos, an
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of these populations should be purs
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affect only a small number of obser
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exposed to fibers considerably long
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the extent to which the material ha
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or statistical power to permit a co
Page 61 and 62: capillaries, whereas insoluble part
Page 63 and 64: mechanisms and increase the rate of
Page 65 and 66: can penetrate their interior to pro
Page 67 and 68: A review for the EPA by an internat
Page 69 and 70: 2.9.4.3.1 Reactive Oxygen Species A
Page 71 and 72: of different types of mineral parti
Page 73 and 74: secreted by mesothelial cells after
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Page 77 and 78: widths are greater for the prismati
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Page 85 and 86: is made of an area larger than a si
Page 87: data are needed to more fully asses
Page 90 and 91: 70 III. Develop improved sampling a
Page 92 and 93: the current paradigm because their
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Page 96 and 97: esponse, and time-course data would
Page 98 and 99: In the second phase of cellular res
Page 100 and 101: 80 • Investigate mechanisms of EM
Page 102 and 103: Research is needed to produce infor
Page 104 and 105: periods that characterize manifesta
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Page 108 and 109: 88 • Develop, validate, and promo
Page 110 and 111: elevant, then an exposure assessmen
Page 114 and 115: established precedence in applying
Page 116 and 117: the mechanisms by which asbestos fi
Page 119 and 120: 4 The Path Forward Developing an in
Page 121 and 122: surveillance investigations. By hav
Page 123 and 124: 5 References Aadchi S, Yoshida S, K
Page 125 and 126: Berman DW, Crump KS [2008b]. A meta
Page 127 and 128: mineral fiber number and epidemiolo
Page 129 and 130: the United States, 1968-81. J Natl
Page 131 and 132: Greim HA [2004]. Research needs to
Page 133 and 134: France: International Agency for Re
Page 135 and 136: millers in New York State. Arch Env
Page 137 and 138: Mandel J (mand0125@umn.edu) [2008].
Page 139 and 140: gpo.gov/2008/pdf/E8-3828.pdf]. Date
Page 141 and 142: Pneumoconioses to Digital Chest Rad
Page 143 and 144: Potter RM [2000]. Method for determ
Page 145 and 146: glass: pleural response in the rat
Page 147 and 148: Vianna NJ, Maslowsky J, Robert S, S
Page 149: Yano E, Wang Z, Wang X [2001]. Canc
Page 152 and 153: efficiency, regardless of sampler o
Page 154 and 155: Table 1. Definitions of general min
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Table 1. Definitions of general min
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Table 1. Definitions of general min
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Table 2. Definitions of specific mi
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safer • healthier • people tm D
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