Environmental asbestos exposure and risk of mesothelioma
Environmental asbestos exposure and risk of mesothelioma Center for Environmental Health Sciences, University of Montana, Missoula, Montana, USA
Correspondence to: Curtis W. Noonan, PhD. Center for Environmental Health Sciences, 32 Campus Drive, the University of Montana, Missoula, MT 59812, USA. Email: curtis.noonan@umontana.edu.
Abstract: Mesothelioma is commonly considered an occupational disease occurring as a result of asbestos exposure in the workplace. Several avenues for environmental asbestos exposures have been described and may be associated with asbestos related disease, including mesothelioma. Worker take-home asbestos, or para-occupational exposure, has been well documented and is the most commonly reported pathway for asbestos exposure among mesothelioma cases that
do not have history of occupational asbestos exposure. Observational studies have evaluated several communities with elevated mesothelioma incidence and environmental exposures attributed to local asbestos-related industries. Potential, but uncertain, mesothelioma risk also may be associated with general population asbestos exposure through contact with asbestos-containing commercial products, particularly housing materials that can be easily disturbed through
activity. Finally, studies have described elevated mesothelioma incidence in several areas where populations are exposed to naturally occurring asbestos materials. These various environmental asbestos exposure pathways are poorly understood, and further studies should be pursued to evaluate their respective importance for population mesothelioma risk.
Keywords: Asbestos; mesothelioma; environmental; para-occupational; naturally occurring asbestos
Malignant mesothelioma is an aggressive form of cancer that typically originates in the pleural but can also occur in the peritoneum, pericardium and around the testes. Asbestos exposure is the only established risk factor known to be causally related to mesothelioma. Mesothelioma and other asbestos related diseases are commonly attributed to occupational exposures. Even in countries that no longer extract asbestos and where commercial uses have
declined, past occupational exposures remain the predominant driver for mesothelioma mortality. However, in recent decades, numerous studies have focused on environmental (i.e., non-occupational) asbestos exposure pathways and risk of mesothelioma.
While occupational exposures are on the wane in some countries, it can be argued that these environmental sources of exposure will account for larger proportions of mesothelioma incidence. Thus, it is imperative to characterize these increasingly important and emerging environmental exposure sources with the likelihood that these pathways will be a growing feature of future mesothelioma risk.
Asbestos is a fibrous mineral with physical and chemical properties that make it resistant to heat and degradation. Such properties have resulted in asbestos fibers being used for a variety of industrial applications, and commercial asbestos is still extracted from open pits. Indeed, world production is expected to remain steady in the near future at approximately two million metric tons with the predominant sources being Brazil, China,
Kazakhstan and Russia (1). Regulated asbestos falls under two classifications: the amphibole group that includes anthophyllite, actinolite, tremolite, amosite and crocidolite and the serpentine group that includes chrysotile. These classifications serve a useful purpose for characterizing extraction products, fiber types used in industry, and, to some degree,
differences in disease risk by fiber type. However, as discussed in the section on naturally occurring asbestos (NOA), reliance on such classifications is limiting when considering environmental exposures and risk of mesothelioma (2). Thus, the term asbestos will be used in this review as the more general term that includes asbestos fibers and the non-regulated fibers that have physical properties similar to commercial asbestos.
In this review we will consider four main categories of non-occupational asbestos exposure (see Figure 1). We begin with exposure pathways that are most closely connected to occupational exposures and industrial practices. Specifically, we consider take-home exposures from asbestos workers, or para-occupational exposure, followed by environmental exposures to communities with large asbestos-related industrial operations. We then discuss the potential
for environmental exposure to asbestos containing products, focusing particularly on fixed-in-place products found in residential settings and vulnerable to disturbance. Finally, we explore the past decades of studies in communities, typically small, that have experienced extensive NOA exposures and opportunities for translating that knowledge to more recently
discovered NOA near large communities. Each of these exposure categories will be presented within the context of what we currently understand with respect to the associated risk for mesothelioma among exposed populations.
