Asbestos Fiber-type and Mesothelioma Risk in the Republic of South Africa

This report focuses on identifying the important asbestos fibertype(s) in the etiology of the asbestos-related cancer mesothelioma. In the last century all three of the commercial fiber types grunerite (amosite) asbestos, chrysotile asbestos and riebeckite (crocidolite) asbestoswere mined, milled and used to fabricate asbestos-containing products in South Afiica. The cases are a consecutive series of occupational and environmental mesotheliomas referred to South Afiica's National Institute for Occupational Health. The authors recovered the inorganic particles from the lung parenchyma in 43 human mesothelioma cases and used analytical transmission electron microscopy to determine the types and concentrations of fibrous minerals present. The predominant, often the only asbestos fiber-type, found in the pulmonary tissues was riebeckite (crocidolite) asbestos. The highest concentration of riebeckite (crocidolite) asbestos found was 10,500,000 fibers per gram of dned lung tissue. The mean concentration was 0.27 million fibers per gram of dned lung tissue which is between 4 to 59-fold below the concentration of chrysotile asbestos in general population where asbestos is found without asbestos-related disease. The results are consistent with the epidemiological reports indicating mesothelioma can develop in individuals with exposures to riebeckite (crocidolite) asbestos described as brief and/or slight.