Response to RE: Gordon R, Fitzgerald S, and Millette J. Asbestos in commercial cosmetic talcum powder as a cause of mesothelioma in women. Int J Occup Environ Health. 2014;20(4):318-332

Inhalation Toxicity of Talc

Respirable talc powder (RTP) is a complex mineral mixture of talc along with accessory minerals, including tremolite, anthophyllite, quartz, magnesite, dolomite, antigorite, lizardite, and chlorite. The industrial mining, milling, and processing of talc ore is associated with elevated incidences of fibrotic and neoplastic diseases, which are also seen among workers exposed to RTP in secondary industries and individuals using processed cosmetic talc for personal use. There is controversial evidence of a link between the talc-induced lung diseases and a potential contamination with asbestos fibers. This controversy is fueled by inadequate exposure data and the complex mineralogy and terminology of the accessory minerals. Talc aerosols exhibit a wide range of mineral habits, including particulates and fibrous structures that have dimensional and compositional characteristics related to the development of asbestos-related lung disease. The inhalation toxicology of RTP is based on the analysis of occupational hygiene and animal inhalation studies conducted between the 1940s and the 1990s and more recent mechanistic studies conducted both in vivo and in vitro. The review of talc toxicity studies reveals that the occupational studies provide only equivocal links between any of the components of the aerosols and the development of pulmonary cancer; however, there is substantial evidence of an association between the aerosols and pleural and pulmonary fibrosis and the development of nonmalignant respiratory disease. The animal inhalation and implantation studies appear to be less than optimal, which also appears to be true for the in vivo and in vitro studies. The mechanistic studies have identified the key pathogenic characteristics of asbestos to be long and thin fibers that are durable in lung tissues and fluids. Talc toxicity studies show that talc particles and fibers are durable and can remain in the lung for up to 40 years after the end of exposure. This extended tissue residence is considered to constitute a continuing tissue exposure that is capable of inducing the documented inflammatory and proliferative response. There is less consensus as to whether there is a threshold fiber length effect, as long, thin fibers (>5 μm) form only a small fraction of talc aerosols and the possible role of fibers >5 μm in the translocation from the lung to the pleura and their association with pleural fibrotic and carcinogenic lesions. Long, thin fibers are preferentially deposited in hot spots in the lung, such as airway bifurcations, areas typically associated with the development of lung cancer. The platy structures typical of talc can form oblate structures behaving more as fibers in the air stream, and these have also been shown to deposit preferentially in such locations. The review of the inhalation toxicity of talc provides a plausible explanation for the carcinogenic potential of RTP.

Anthophyllite asbestos: state of the science review

Anthophyllite is an amphibole form of asbestos historically used in only a limited number of products. No published resource currently exists that offers a complete overview of anthophyllite toxicity or of its effects on exposed human populations. We performed a review focusing on how anthophyllite toxicity was understood over time by conducting a comprehensive search of publicly available documents that discussed the use, mining, properties, toxicity, exposure and potential health effects of anthophyllite. Over 200 documents were identified; 114 contained relevant and useful information which we present chronologically in this assessment. Our analysis confirms that anthophyllite toxicity has not been well studied compared to other asbestos types. We found that toxicology studies in animals from the 1970s onward have indicated that, at sufficient doses, anthophyllite can cause asbestosis, lung cancer and mesothelioma. Studies of Finnish anthophyllite miners, conducted in the 1970s, found an increased incidence of asbestosis and lung cancer, but not mesothelioma. Not until the mid-1990s was an epidemiological link with mesothelioma in humans observed. Its presence in talc has been of recent significance in relation to potential asbestos exposure through the use of talc-containing products. Characterizing the health risks of anthophyllite is difficult, and distinguishing between its asbestiform and non-asbestiform mineral form is essential from both a toxicological and regulatory perspective. Anthophyllite toxicity has generally been assumed to be similar to other amphiboles from a regulatory standpoint, but some notable exceptions exist. In order to reach a more clear understanding of anthophyllite toxicity, significant additional study is needed. Copyright © 2016 John Wiley & Sons, Ltd.