Although asbestos is no longer mined in the United States, prior and ongoing exposures to asbestos continue to contribute to respiratory diseases, including mesothelioma, lung cancer, and asbestosis. Asbestos exposures are estimated to have contributed to 18,068 deaths from mesothelioma in the United States from 1999–2005; asbestos-related diseases continue to be diagnosed due to the long latency period for their manifestation. U.S. workers and residents, for example, may continue to undergo hazardous exposures due to unremediated asbestos-containing materials, imported asbestos-containing products, and natural environmental occurrences of asbestos. 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.
To examine ongoing issues and concerns in this field, the National Institute for Occupational Safety and Health (NIOSH) drafted a research roadmap, Asbestos Fibers and Other Elongated Mineral Particles: State of the Science and Roadmap for Research (hereafter called the Roadmap), that provides an overview of the state of the science and a plan for future research in areas including toxicology, mineralogy, epidemiology, and exposure assessment. The focus of the proposed research is on clarifying the relationship between human health effects and the physical and chemical characteristics (e.g., mineralogy, morphology, dimension, surface properties) of a wide range of elongate mineral particles (see definition of elongate mineral particles below). In 2008, NIOSH asked the
Institute of Medicine (IOM) and the National Research Council (NRC) to form a committee to provide a review of the scientific and technical quality of the January 2009 draft NIOSH Roadmap document. This report provides the committee’s assessment of the Roadmap and recommendations for strengthening its utility for NIOSH, other federal agencies, the private sector, and other stakeholders.
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. The current regulatory definitions used by the Occupational Safety and Health Administration (OSHA) and the Mine Safety and Health Administration (MSHA) define six recognized minerals1 as varieties of asbestos.
NIOSH recognized the need for a term to encompass a broad class of mineral particles of specific size and dimension that are the primary focus of the proposed research in the Roadmap and introduced the term elongated mineral particles2 to attempt to capture this broad range of mineral particles. The committee considers the dimensions described in the NIOSH Roadmap definition (“longer than 5 μm with a minimum aspect ratio of 3:1”) as a good starting point for research. The term elongate mineral particles is a convenient, neutral, and unified means of describing various minerals across different professional disciplines but
is not a rigorous mineralogical classification or one to which regulatory significance is assigned.
The committee makes suggestions regarding improving the scientific rigor of the glossary definitions and use of terminology and nomenclature and believes that this increased specificity will aid in clarifying the central focus of the Roadmap, which is to determine which elongate mineral particles (specific types of minerals or specific physical or chemical characteristics) have potential negative impacts on human health.
Throughout this report, the committee notes the value of the Roadmap document in bringing together a substantial body of research across several varying disciplines. 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 exposures, epidemiology, and sampling or analytical methods? Should any of the content of this section be modified, based on the state of scientific understanding of these issues? Are there any significant studies that have been overlooked?
Finding 1: The NIOSH Roadmap is generally consistent with the state of scientific understanding of the toxicity, occupational exposures, epidemiology, and sampling or analytical methods. The committee identified several areas that could be strengthened and references those areas in the narrative and in the committee recommendations. The Roadmap would be made more coherent and useful if it included or refined four key components: vision or purpose, rationale, goals, and framework (systematic plan for conducting the research).
Statement of Task Question 2: Does the document clearly and adequately explain the scientific rationale for research on the mineralogy, morphology, dimensions, and surface characteristics of elon-
gate mineral particles, and is its treatment of this issue consistent with the state of scientific understanding of the toxicity, occupational exposures, and epidemiology of elongate mineral particles?
Finding 2: The Roadmap explains the scientific rationale for research on the mineralogy, morphology, dimensions, and surface characteristics of elongate mineral particles. This is presented primarily through discussions of toxicological studies of asbestos and of synthetic fibers that provide the background on why research is needed to examine mineral particle characteristics and their impact on toxicity. However, the mineralogical discussions were found lacking in many areas. Adding more information on the occupational and environmental health rationale for research in this area would be helpful, including available data on the types of occupations and environmental situations likely to result in exposure to more specific types of elongate mineral particles. As noted in its recommendations the committee urges that the Roadmap include a clear statement of the overarching vision for the research. The committee 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? Should any of the discussed issues be omitted or revised, based on the state of scientific understanding of these issues? Are there any significant issues that should be added?
Finding 3: The NIOSH Roadmap provides a reasonable discussion of some of the significant issues regarding mineralogy, morphology, dimensions, and surface characteristics of elongate mineral particles as related to their potential to cause disease, but
as noted in response to Question 4 below, the committee urges a greater emphasis on the relevant mineralogical research, in particular on mineralogical characterization. The committee notes significant inconsistencies and deficiencies in mineralogical terminology and nomenclature and provides a series of recommendations to clarify and make more rigorous, consistent, and complete the terminology used in the text and the glossary in the Roadmap.
Statement of Task Question 4: Is the research proposed likely to effectively 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 issues? Is there any significant research that should be added?
Finding 4: The research effort proposed is likely to address some of the most significant issues regarding mineralogy, morphology, dimensions, and surface characteristics of elongate mineral particles. However, as noted throughout this report and in its recommendations, the committee calls for more details to be included on mineralogical research, with an emphasis on a systematic approach to characterization of the minerals that is integrated in a meaningful way into toxicological and other studies to better understand the relative disease-causing potential of a range of elongate mineral particles relevant to human exposures. This effort is part of a consistent strategy for characterizing and testing the relative toxicities of elongate mineral particles and mixtures. Exploration of additional opportunities for epidemiological research is needed as well as careful examination of the exposure assessment methodologies. The effort is likely to be more successful if it involves interdisciplinary collaboration and integration.
Statement of Task Question 5: Was the process that was used to develop and revise the document and that is described in the Foreword,
including the mechanisms for input from the scientific and stakeholder communities, appropriate from a scientific perspective?
Finding 5: The process used by NIOSH to develop and revise the document that is described in the Foreword was, in the opinion of the committee, generally appropriate in being open and transparent with multiple opportunities for input into the Roadmap document. The process would have benefited from greater involvement of the mineralogical community throughout its formulation. An interdisciplinary approach may have been better applied in the development process.
Clarify Roadmap Structure and Vision
Because the NIOSH Roadmap brings together a great deal of information and a wealth of ideas on future directions for research, it is necessary for the document to have a clearly stated vision and rationale. The details of the Roadmap can all too easily overtake the view of the larger objective, and therefore the committee urges that the vision and rationale be clearly laid out in the early part of the Roadmap. 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 overarching vision and rationale for the research program.
The overarching vision should point toward research that will differentiate effects from exposure to a range of elongate mineral particles and help determine the influence of size, shape, and other physical and chemical characteristics of these particles on human health. This
research would identify which elongate mineral particles, or what characteristics of those particles, should be included in recommendations to protect the public and workers from hazardous occupational and environmental exposures.
The rationale for the Roadmap should clearly articulate the influence that ongoing and future research can have on improving public and occupational health.
A clearer vision and purpose would help strengthen the goals that the research is intended to support. The research should be prioritized as to the hazard and exposure.
Recommendation 2 Include Key Components
NIOSH should ensure that four key components are included or refined in the Roadmap: (1) vision, (2) rationale, (3) goals, and (4) framework.
Terminology and nomenclature have been an ongoing challenge for this area of research. Because of the ambiguous and confusing terms for asbestos and other mineral particles used in the past, it is important for the Roadmap to place strong emphasis on specificity in its use of terminology and nomenclature and on providing references to definitions from standard reference texts in each field. The Roadmap needs definitions for all technical terms, given the interdisciplinary nature of the research. 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.
Recommendation 3 Improve Terminology
NIOSH should revise its Roadmap with careful attention to consistency in the use of nomenclature and terminology. The goal is
that authoritative terminology should permeate research and regulatory efforts, specifically:
For research purposes, the term elongate mineral particles is useful for encompassing a broad category of mineral particles of a certain dimension and aspect ratio; more specific mineralogical terminology would be needed for regulatory purposes;
Revisions should be made to the Roadmap glossary using accepted mineralogical terminology or nomenclature from the current American Geological Institute’s Glossary of Geology or other standard texts; citations should be provided for each definition; nonstandard terms should be removed from the glossary and the main text; and
Terminology used in sections referring to epidemiology and toxicology should also use definitions from current standard texts and be included in the glossary with citations.
Strengthen the Emphasis on Mineralogy
The Roadmap outlines a set of studies to improve knowledge on the potential health effects of elongate mineral particles and the ways in which human exposures could best be studied. 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. Similarly, toxicological experiments require well-characterized reference mineral samples to allow systematic intra- and interlaboratory comparisons of results. While the Roadmap notes the need for standardized reference minerals, the committee believes that there is a need for a more detailed approach for developing a central repository of these samples. Priorities for the repository should focus on those minerals with the greatest potential for human exposures. Although the epidemiological and toxicological dis-
cussions in the Roadmap were generally thorough, greater depth and rigor is needed in the mineralogical discussions.
Recommendation 4 Strengthen the Emphasis on Mineralogical Research
NIOSH should revise the Roadmap to give greater attention to the mineralogical foundations of the proposed research. Discussions of mineralogy in the Roadmap should be strengthened by incorporating current understanding in this field using accepted terminology and by proposing research on the fundamental mineralogical properties relevant to toxicology, epidemiology, and exposure assessment. Specifically, mineralogical research is needed on physical and chemical properties, biopersistence, and mineral source characterization, including the development of standard sets of tests and methodologies.
Recommendation 5 Develop a Reference Mineral Repository
NIOSH should work with other federal agencies and organizations to develop a repository of well-characterized and standardized reference minerals for use in research.
Focus the Research Efforts
NIOSH has put together a comprehensive and broad-based research Roadmap that could be improved through further emphasis on implementing a systematic and interdisciplinary approach to the outlined research. 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. Because asbestosis, lung cancer, and mesothelioma likely have different mechanisms of pathogenesis, attention must be given to selecting an array of in vitro assays capable of detecting cellular events thought to be involved in pathways leading to each outcome of concern.
A wider focus in epidemiological studies and new approaches to exposure assessment will also be of great benefit in addressing these issues.
Recommendation 6 Emphasize Interdisciplinary Efforts
NIOSH should revise the Roadmap to emphasize the need for collaboration and integration of research among the mineralogical, toxicological, epidemiological, and exposure assessment disciplines.
Recommendation 7 Develop a Systematic Strategy for the Toxicological Assessment of Elongate Mineral Particles
NIOSH should revise the Roadmap to describe a systematic tiered strategy for characterizing and testing the relative toxicities of elongate mineral particles and/or their mixtures. The strategy should include the following:
Characterizing the chemical and physical properties of the elongate mineral particles beginning with petrographic analysis and proceeding through X-ray diffraction, transmission and scanning electron microscopy, and other techniques; and
Using tiered panels of in vitro and in vivo assays of increasing complexity to identify and characterize biological 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 including studies of Libby, Montana, worker and resident populations, as well as cohorts exposed to elongate mineral particles in other countries; and
Statistical methods for addressing analytic variability and determining the relationships between mineralogical and exposure variables and health outcomes.
STEPS TOWARD A RESEARCH STRATEGY
A research roadmap is one component of a larger research strategy. The final section of the NIOSH Roadmap notes that the research agenda “will require a substantial investment of time, scientific talent, and resources by NIOSH and its partners to formulate research programs and prioritize research projects to achieve the proposed goals.” The committee urges NIOSH to continue its work with other federal agencies (e.g., the U.S. Environmental Protection Agency, the National Institute of Environmental Health Sciences, the U.S. Geological Survey, the Occupational Safety and Health Administration, the Mine Safety and Health Administration, and the Agency for Toxic Substances and Disease Registry) 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. Too often research programs present broad goals for important research but do not back them up with a concrete and realistic plan for accomplishing the goals.
Such a strategy might contain, in addition to the research framework and goals elaborated in the NIOSH Roadmap, the following elements:
An interdisciplinary system for prioritizing research activities to ensure maximum efficiency in an environment in which not everything possible can reasonably be undertaken at once and multiple disciplines need to work together to determine the priorities;
An approximation of the resources needed to carry out high- and middle-priority efforts; and
A plan for review, evaluation, and accountability for those receiving support for research contained in the Roadmap.
As NIOSH and other partners move forward in implementing the Roadmap, discussions are needed on successful models of establishing effective partnerships and management of research efforts to ensure a coordinated approach to address specific information gaps.