Sources and types of mineral dust in regions of Turkey with endemic malignant mesothelioma

It has been proposed that the observed high incidence of fibre-related diseases, particularly malignant pleural mesothelioma (MPM), in Turkey can serve as a surrogate indicator of exposure to natural mineral fibres. Environmental exposure to the amphibole tremolite and the zeolite erionite are almost certainly the cause of this disease in the areas of Turkey where these minerals are found. In this study, field reconnaissance and mineralogical investigations were conducted to provide information to evaluate the environmental impacts of minerals in these endemic MPM regions. Some published data has also been re-evaluated and correlated with the current study. The results help to confirm that prolonged out-door and in-door exposure to these various mineral fibres may be the cause of MPM. Mixed fibres of tremolite-actinolite, anthophyllite, crocidolite, chrysotile and silica have been found in the asbestos-rich-regions where the disease is endemic. Fibre dimension is known to be a critical factor in the development of MPM and other mineral fibre-related diseases and so in addition to other studies the type and form of these minerals was examined. In the locations where non-fibrous tremolite and chrysotile-like minerals were present instead of endemic MPM, a high incidence of calcified pleural plaques (CPP) and pleural thickening (PT) was observed. Although examples of the zeolite group of minerals have been found in various locations throughout Turkey, only in Central Anatolia is erionite found in a fine fibrous form. This is the only area of Turkey where MPM is considered to be endemic through exposure to that form of the mineral. The studies also indicate that beside erionite, other fibres such as actinolite, tremolite, crocidolite, chrysotile, crystalline silica (cristobalite) and volcanic glass shards are present in the environment, and are found in human and sheep lung tissue samples.