A Review of the NIOSH Roadmap for Research on Asbestos Fibers and Other Elongate Mineral Particles (2009) / Chapter Skim
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Internationally, asbestos continues to be mined and used in manufacturing in a number of countries because of its desirable commercial properties such as strength and heat resistance. Ongoing issues include potential health effects in workplaces and in situ environmental settings as well as exposures to mineralogical mixtures that may contain asbestos and exposures to nonasbestiform elongate mineral particles of similar size and shape to asbestos particles.
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TERMINOLOGY: ASBESTOS AND OTHER ELONGATE MINERAL PARTICLES One of the major challenges faced in conducting research in this field is the terminology. Because the term asbestos does not denote a single mineral but rather is used to encompass a set of minerals with specific industrial characteristics and commercial value, there have been challenges and controversies in determining both what specific set of minerals and what set of characteristics should be included in a definition of asbestos.
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The committee was charged with providing a review of the Roadmap document and answering five specific questions detailed below. Statement of Task Question 1: Is the document consistent with the state of scientific understanding of the toxicity, occupational expo sures, epidemiology, and sampling or analytical methods?
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The commit tee also believes that since the term elongate mineral particle covers a broad range of mineral particles of interest in this research, its use should be limited to research efforts and emphasizes that this term is not a rigorous mineralogical term. Statement of Task Question 3: Does the document discuss the most significant issues regarding mineralogy, morphology, dimensions, and surface characteristics of elongate mineral particles?
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Statement of Task Question 4: Is the research proposed likely to ef fectively address the most significant issues regarding mineralogy, morphology, dimensions, and surface characteristics of elongate mineral particles? Should any of the discussed research be omitted or revised, based on the state of scientific understanding of these is sues?
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Further, it is the committee's hope that a more systematic and tiered approach to the research agenda will allow research to be conducted in a manner that will answer the questions regarding which physical and chemical characteristics of elongate mineral particles are primary determinants of toxicity to humans, thus allowing unambiguous identification of specific types of mineral particles that would be of concern to human health. Recommendation 1 Clarify the Vision and Rationale NIOSH should revise the Roadmap to clearly state the overarch ing vision and rationale for the research program.
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The umbrella term elongate mineral particles provides an important starting point for discussions on the broad range of mineral particles under investigation. However, because considerable uncertainty remains regarding the range of potential toxicities within the spectrum of elongate mineral particles, it is the committee's view that at this time the term elongate mineral particles should not be used for regulatory purposes.
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A key piece of this research plan is the development of well-characterized reference mineral samples that could then be incorporated in toxicological studies to assess the variability in the toxicity of different types of elongate mineral particles. The identification, classification, and characterization of unknown mineral particles from workplace or environmental exposures require knowledge of and comparison to similar, well-characterized mineral particles and associated geological locales.
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Improved efforts on characterizing the elongate mineral particles used in toxicological research could go a long way toward ensuring that study results can be compared. Additionally, using a tiered systematic process to study the toxicity of various types of particles would assist in bringing clarity to the range of toxicities and help to identify any specific mineralogical properties of concern to human health.
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The strategy should include the following: • Characterizing the chemical and physical properties of the elongate mineral particles beginning with petro graphic analysis and proceeding through X-ray diffrac tion, transmission and scanning electron microscopy, and other techniques; and • Using tiered panels of in vitro and in vivo assays of in creasing complexity to identify and characterize biologi cal responses and categorize the potential hazards. Recommendation 8 Emphasize Additional Research Areas NIOSH should revise the Roadmap to include an emphasis on the following: • Incorporating petrographic analysis and developing new exposure assessment tools using electron microscopy methods that are mineralogically and toxicologically relevant and that minimize reliance on phase contrast microscopy methods; • Toxicological mechanisms of action of a range of well characterized elongate mineral particles with attention to early biomarkers of human health effects; • Additional opportunities for epidemiological research in cluding studies of Libby, Montana, worker and resident populations, as well as cohorts exposed to elongate min eral particles in other countries; and • Statistical methods for addressing analytic variability and determining the relationships between mineralogical and exposure variables and health outcomes.
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and private-sector and nonprofit organizations with a focus on developing a research strategy that details the resources, priorities, responsibilities, and commitments needed to accomplish and evaluate this research effort. Many of the issues that require additional research to better understand the relative disease-causing potential of various types of elongate mineral particles are common both to the fields of occupational health, as pertaining to work-related exposures, and environmental health, as related to exposure of the general public.
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