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

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70 III. Develop improved sampling and analytical methods for asbestos fibers and other EMPs [3.4]. • Reduce inter-operator and inter-laboratory variability of the current analytical methods used for asbestos fibers [3.4.1]; • Develop analytical methods with improved sensitivity to visualize thinner EMPs to ensure a more complete evaluation of airborne exposures [3.4.2]; • Develop a practical analytical method for air samples to differentiate between exposures to asbestiform fibers from the asbestos minerals and exposures to EMPs from their nonasbestiform analogs [3.4.3]; • Develop analytical methods to assess durability of EMPs [3.4.4]; and • Develop and validate size-selective sampling methods for EMPs [3.4.5]. 3.2 An Approach to Conducting Interdisciplinary Research Within each of the goals and objectives laid out in this framework, a more detailed research program will have to be developed. Research to support these three goals must be planned and conducted by means of an interdisciplinary approach, incorporating toxicological, epidemiological, exposure assessment, medical, analytical, and mineralogical methods. The research must also be integrated to optimize resources, facilitate the simultaneous collection of data, and ensure, to the extent feasible, that the research builds toward a resolution of the key issues. An aim of the research is to acquire a level of mechanistic understanding that can provide the basis for developing biologically-based models for extrapolating results of animal inhalation and other types of in vivo studies to exposure conditions typically encountered in the workplace. The information gained from such research can then be used by regulatory agencies and occupational health professionals to implement appropriate exposure limits and risk management programs for monitoring worker exposure and health. Much of this research may be accomplished by NIOSH, other federal agencies, or other stakeholders. Any individual research project undertaken should be designed to ensure that the results can be interpreted and applied within the context of other studies in the overall program and lead to outcomes useful for decision-making and policy-setting. 3.3 National Reference Repository of Minerals and Information System To support the needed research, a national reference repository of samples of asbestos and related minerals will be required, and a database of relevant information should be developed. Minerals vary in composition and morphology by location and origin, and differences within the same mineral type can be significant. Currently, no national repository exists to retain, document, and distribute samples of asbestiform and nonasbestiform reference minerals for research and testing. These reference samples should be well-characterized research-grade materials that NIOSH CIB 62 • Asbestos
are made available to the research community for testing and standardization. This will allow minerals with matching properties (e.g., morphology, dimension) to be chosen for study. To accomplish this research, exhaustive characterization of the samples, including contaminants, is necessary. Detailed characterizations of minerals should include their ability to affect biological activities and properties such as (1) purity, (2) particle morphology (range of dimensions and sizes), (3) surface area, (4) surface chemistry, and (5) surface reactivity. The particle characteristics identified by Hochella [1993] should be considered for particle characterization. The use of these samples in research would facilitate meaningful comparisons and reduce uncertainties in the interpretation of results between and among studies. Care must be taken to ensure that a sufficient amount of the studied material is available, not only for current studies, but also as reference material for possible future studies. The repository should accept and store samples from researchers conducting EMP studies so that further testing and characterizations can be performed. The information developed from all of these efforts should be entered into a database, which can serve as a tool for selection of minerals for testing and validation of toxicological tests, as well as to assist in identification of worker populations for possible epidemiological studies. The development of a comprehensive, publicly available information system incorporating all studies of the toxicity, exposures, and health effects of asbestos and related minerals could help enhance the development of the research programs, avoid duplication of effort, and enhance interpretation of the data generated. The system should include all pertinent information about methods, doses or exposures, minerals, particle characteristics, and other topics. NIOSH CIB 62 • Asbestos 3.4 Develop a Broader Understanding of the Important Determinants of Toxicity for Asbestos Fibers and Other EMPs To address this objective, one of the first steps will be to identify the range of minerals and mineral habits needed to systematically address the mineral characteristics that may determine particle toxicity. Care must be taken to ensure that mineralogical issues in a study are adequately addressed. Information on both crystalline lattice structure and composition is needed to define a mineral species, because information on either alone is insufficient to describe the properties of a mineral. For example, nonasbestiform riebeckite and asbestiform riebeckite (crocidolite) share the same elemental composition but have different expressions of their crystalline lattices. EMPs from nonasbestiform riebeckite are not flexible. Crocidolite fibers generally have chain-width defects, which explain their flexibility. These chainwidth defects also affect diffusion of cations and dissolution properties, both of which can explain greater release of iron into surrounding fluid by crocidolite than by nonasbestiform riebeckite [Guthrie 1997]. In addition to elemental content and crystalline habit, the particle characteristics identified by Hochella [1993] should be considered for particle characterization. For example, the current paradigm for fiber pathogenicity does not discriminate between different compositions of biopersistent fibers, except insofar as composition determines biopersistence. Two biopersistent fiber types, erionite [Wagner et al. 1985] and silicon carbide [Davis et al. 1996], show a special proclivity to cause mesothelioma, for reasons that are not easily explained by 71
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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
Page 39 and 40: of airborne asbestos fibers was fir
Page 41 and 42: which the deposits have been report
Page 43 and 44: with the most pronounced excess of
Page 45 and 46: A limitation of the epidemiological
Page 47 and 48: CI = 1.8-6.7) was noted in the earl
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Page 51 and 52: of these populations should be purs
Page 53 and 54: affect only a small number of obser
Page 55 and 56: exposed to fibers considerably long
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Page 59 and 60: 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
Page 79 and 80: concluded that asbestos fibers
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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
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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
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Page 114 and 115: established precedence in applying
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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
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Pneumoconioses to Digital Chest Rad
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Potter RM [2000]. Method for determ
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glass: pleural response in the rat
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Vianna NJ, Maslowsky J, Robert S, S
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Yano E, Wang Z, Wang X [2001]. Canc
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efficiency, regardless of sampler o
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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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