Preface

In the twenty‐first century, asbestos remains a serious occupational and environmental hazard. First, asbestos is still produced in different countries and widely used in China, Latin America, and other regions. Second, asbestos is present in numerous buildings, equipment, and the environment as a legacy from the times when it was most actively utilized. Third, naturally occurring asbestos (NOA) is present in soil and rocks as a contaminant presenting a possible hazard for various human activities worldwide. It has been long recognized that human exposure to multiple types of unregulated fibrous minerals, which sometimes do not fit the traditional definitions of asbestos, may have similar potential health consequences as commercial asbestos itself. Some examples of asbestiform minerals include erionite, fluoro‐edenite, and balangeroite, among others. Also, various minerals, when affected by mechanical force, can produce so‐called cleavage fragments that may resemble asbestos fibers by chemical composition, but they typically do not have the same size distribution, rigidity, lung penetration rate, and biopersistence as asbestos fibers.

In quantitatively and qualitatively estimating the degree of potential adverse effects from exposure to asbestos and other fibrous minerals, health risk assessment allows for evaluation and prioritization of potential control and other related actions. This book is intended to summarize approaches for quantitative risk assessment in applications to asbestos and its analogs, using the most recent mineralogical assessment, epidemiological data, and toxicological concepts. The book also aims to fill in voids in the scientific literature on asbestos and other fibrous mineral risk assessment methodologies and to demonstrate practical applications of risk quantification and characterization.

The science of health risk assessment involves integration of epidemiological, toxicological, industrial hygiene, medical, and environmental evaluation expertise to identify hazards, measure or estimate exposure levels, determine dose–response relationships for various health effects, and characterize risks of specific diseases. Thus, authors of the book chapters have multidisciplinary backgrounds. Our intention was to invite among the most advanced scientists working in the area of asbestos research, aiming to update the major works published in this area and suggest future research needs.

The past decades brought better understanding of the significant differences in various characteristics of fibrous minerals. Erionite fibers from Cappadocia, Turkey, became a confirmed factor in the local mesothelioma epidemic in a magnitude never observed for other types of fibers. Chrysotile fibers were convincingly demonstrated to have biopersistence in human lungs in the range of several months versus amphiboles with half‐life in lungs of several decades. It was shown that asbestiform mineral fibers can be distinguished from non‐asbestiform varieties, or cleavage fragments, by characterizing size distribution. Many epidemiological studies found deviations in cancer potency not only between mineral types of fibers but for varieties of the same mineral type (for example, between textile and non‐textile chrysotile). While all types of asbestiform mineral fibers are potentially carcinogenic, the difference in potency factors for various minerals can reach the magnitude of several thousands. The quantitative risk assessment is a valuable tool to apply the knowledge about characteristics of fibers to specific exposure levels, not to achieve universal “100% safety” goals but to compare realistic predictions of the health outcomes for various scenarios and types of fibrous and nonfibrous agents and help determine priorities for interventions.

It should be noted that differences in cancer potency between various types of mineral fibers are still rarely considered in the regulations. For many of the fibrous minerals (like erionite), there are no established regulatory exposure limits. However, quantitative risk assessment becomes a tool of choice for many regulators internationally. The readers of this book will see how different approaches to asbestos risk assessment can be reconciled if better understanding of the available mineralogical, toxicological, epidemiological, and other relevant information about asbestos would be employed by regulators. We will demonstrate that attempts to equalize the regulatory limits for all types of asbestos would sometimes cause under‐protection of workers in various industries. Application of quantitative risk assessment should help environmental and occupational health professionals evaluate health hazards related to various mineral types of fibers realistically, based on the most recent scientific results and approaches.

In our book, we followed the structural paradigm of the risk assessment procedure as described by the National Research Council (National Academies of Sciences) (NRC/NAS).1,2 Based on the paradigm, Stage 1 of risk assessment is considered “planning”, and Stage 2 consists of the following:

• Hazard Identification
• Exposure Assessment
• Dose–Response Assessment
• Risk Characterization

Accordingly, this book is also organized into four sections representing the four steps of the risk assessment process by NRC/NAS. Each section contains chapters describing relevant scientific achievements and developed methodologies for the risk assessment.

An attempt has been made to focus our narrative on important and complex issues such as defining terms of asbestos, asbestiform, cleavage fragments, and elongate mineral particles; major mechanisms of asbestos toxicity along with potential health effects of exposure; pathological indications of asbestos exposure and disease; historical asbestos testing methods and comparability with current techniques; exposure assessment methodology and validation; comparison and utilization of various meta‐analytical data for risk assessment purposes; mathematical modeling of risk; and practical adaptation of scientific results for retrospective, current, and perspective risk characterization. Several case studies of asbestos risk assessment will be demonstrated.

This book was not intended to cover every possible aspect of asbestos risk assessment. Further studies are needed to improve our understanding of specific mechanisms for asbestos carcinogenicity. There is a need for further epidemiological studies in the cohorts exposed to commercial and naturally occurring asbestos. The issues of the role of fiber size distribution in carcinogenic potential of asbestos as well as deep exploration of the differences between asbestiform and non‐asbestiform minerals in their toxic effects probably deserve a separate book to be developed. There are obvious limitations in the scope of this book: for example, we focused on the carcinogenic asbestos risks, though additional steps can be suggested to develop similar methodology for nonmalignant health outcomes such as pleural plaque and pulmonary asbestosis.

We anticipate that dose–response science for asbestos will continue its development in the future. Further studies are needed to fully clarify the issues of possible nonlinearity for asbestos risks as a function of exposure. At some level of low cumulative exposure, a threshold model for asbestos risk may appear to be quite realistic for noncarcinogenic, but also for carcinogenic outcomes. Scientific exploration of the risk assessment paradigm requires understanding of uncertainties and limitations in the methodology, which may define areas of future research.

The editors are grateful to the contributors of the book chapters, but also to the wide group of scientists who helped our better understanding of the risk assessment methodology. We especially appreciate our discussions with Professor Julian Peto, Dr. D. Wayne Berman, John Hodgson, Dr. Victor Roggli, and many others. It should be noted that our coauthors, Dr. Ann Wylie, Dr. Bruce Case, Dr. Brooke Mossman, Dr. Garry Burdett, Lucy Darnton, Dan Hall, and Arseniy Korchevskiy, not only worked on their own chapters but also helped us organize all the process of work and review various materials included to the book. At the same time, the editors acknowledge that the opinions of the authors for different chapters may not always reflect the position of the editors. Also, the authors are responsible for the accuracy of their references and quotations, as well as for the quality of data used in their studies.

The editors appreciate the work of Debbie Vaughan who processed the entire book, helping with the editing, proofreading, and organization of the chapters.

The editors especially thank Wiley for the support in the preparation of this book and for recognizing the potential scientific need.

The editors also dedicate the book to the memory of Sue Rasmuson, the wife, the mother, and the friend, who was the inspiration for this project when it only started. We also are grateful to our entire families for their support and love.

Notes

1. 1 National Research Council (US) Committee on Improving Risk Analysis Approaches Used by the U.S. EPA. (2009). Science and Decisions: Advancing Risk Assessment. Washington (DC): National Academies Press (US). https://doi.org/10.17226/12209.
2. 2 The National Academies of Science, Engineering, Medicine. (2017). Using 21st Century...