Historical state of knowledge of the health risks of asbestos posed to seamen on merchant ships

Abstract

We examined the development of knowledge concerning the risks posed by asbestos to seamen working aboard merchant ships at sea (i.e. commercial, rather than naval vessels). Seamen were potentially exposed to “in-place” asbestos on merchant ships by performing intermittent repair and maintenance tasks. We reviewed studies measuring airborne asbestos onboard merchant ships and health outcomes of merchant seamen, as well as studies, communications, and actions of U.S. organizations with roles in maritime health and safety. Up to the 1970s, most knowledge of the health risks of asbestos was derived from studies of workers in asbestos product manufacturing and asbestos mining and milling industries, and certain end-users of asbestos products (particularly insulators). We found that attention to the potential health risks of asbestos to merchant seamen began in the mid- to late 1970s and early 1980s. Findings of pleural abnormalities in U.S. seamen elicited some concern from governmental and industry/labor organizations, but airborne asbestos concentrations aboard merchant ships were found to be <1 f/cc for most short-term repair and maintenance tasks. Responses to this evolving information served to warn seamen and the merchant shipping industry and led to increased precautions regarding asbestos exposure. Starting in the 1990s, findings of modest increases in lung cancer and/or mesothelioma in some epidemiology studies of seamen led some authors to propose that a causal link between shipboard exposures and asbestos-related diseases existed. Limitations in these studies, however, together with mostly unremarkable measures of airborne asbestos on merchant ships, preclude definitive conclusions in this regard.

• Asbestos
• historical state of knowledge
• lung cancer
• merchant marine
• mesothelioma
• U.S. Coast Guard
• OSHA
• seamen

Acknowledgments

The authors wish to thank Tom Lewandowski for his technical assistance, and Jasmine Lai and Jessica Goldstein for their assistance with manuscript preparation.

Declaration of interest

Both authors have served as experts in asbestos litigation. The underlying research and collection of documents for this paper was, for the most part, performed during preparations of experts in anticipation of litigation and this effort was funded by law firms for defendants. Neither the law firms nor defendants, however, asked that this paper be written or published. The preparation of this manuscript was supported only by the authors and their employer (Gradient), and its conclusions are exclusively those of the authors. Aside from the authors and internal Gradient reviewers, no one has commented on or revised this manuscript prior to its submission.

Notes

¹ Case reports describe the experience of a single individual or group of individuals with a similar disease, and may be useful for generating hypotheses for epidemiology studies. Because they tend to focus on the exposed with disease, however, and do not include appropriate comparisons to the exposed without the disease or the unexposed with or without the disease, they are not reliable for identifying new etiological associations (Olsen et al., 2014).

² Methods and metrics for measuring or estimating asbestos concentrations have varied over time. An early impinger method expressed total fiber/dust concentrations as million particles per cubic foot (mppcf). Since the 1960s, a membrane filter method has been commonly used; it expresses sampling data in units of fibers per cubic centimeter (f/cc). The most widely used conversion factor has been 1 mppcf ≅ 6 f/cc, but other conversion factors, ranging from 1:1 (mppcf to f/cc) to 1:10, have also been used (Williams et al., 2007).

³ Lagging is a material, such as cloth, millboard, and finishing cement, that is applied over insulating materials to provide support and protection from damage (Hollins et al., 2009).

⁴ We are not aware of any studies exploring other cancer types or other non-cancer diseases (i.e. health endpoints less directly associated with asbestos) in seamen explicitly as a potential consequence of asbestos exposure.

⁵ While lack of complete knowledge of prior occupational or nonoccupational asbestos exposures of a particular population is a limitation in many studies, a concern in studies of seamen is that prior land-based occupations (e.g. work in shipyards) may have provided relatively greater contributions to cumulative asbestos exposure than working aboard ships.

⁶ The study by Roggli et al. (2002) may have included US merchant seamen, but does not provide information regarding the number and outcomes for such cases. As noted earlier, Kelman & Kavaler (1990) presented no data on the smoking status of its study subjects.

⁷ The evidence with regard to seamen in the U.S. is relatively sparse.