Meral Došan
Department of Geological Engineering, Hacettepe University, Ankara
e-mail: doganme@hacettepe.edu.tr
Epidemiological studies have demonstrated strong correlations between exposure to mineral
fibers and a variety of pulmonary diseases, including fibrosis, lung carcinoma, and a type of
pleural and peritoneal cancer known as mesothelioma. The incidence of cancer is increasing in a
number of industrialized countries. Within a few years in the U.K., for example, mesothelioma will
be a 1% cause of death in men (Peto et al. 1995, 1999). Mesotheliomas are the most important primary
pleural neoplasms. Incidence of mesothelioma is extremely high in Turkey. There are crucial
questions to ask:
I-Why is the cancer rate is extremely high in Turkey ?
II-What is the source of exposure ?
III-Why do some families in Turkey have more incidence of cancer than average ?
IV-Can sensitive sub-populations be identify ?
V-Are there confounding factors ?
VI- Why do we not have similar cancer rates reported from other regions in the world where people
may be exposed to the similar type mineral dusts ?
VII-Are there differences between Turkish and other mineral dust occurrences ?
VIII-What is the route of exposure-inhalation or transplacental ?
IX-What can be done to reduce or eliminate mineral dusts related diseases ?
Item II, III, VI, VII and IX are directly related with minerals.
Vast amount of mineral dust are produced by erosion of natural deposits at the surface of soil due to heavy fracturing, poor vegetation, and climatic conditions in various parts of Turkey. Rural exposure was enhanced by various human activities including agriculture and exposure to indoor sources such as white stucco, wall paint, insulation material, and mining. Type, dose factors, concentration, duration of exposure and morphology of mineral dust may be associated with several diseases including cancer.
Mineral dust related diseases, and tremolite and erionite depending upon the area were reported as major cause from different parts of Turkey over the years. However, environmental and mineralogical studies in various parts of Turkey indicate that high levels of mixed fibers such as chrysotile, tremolite, anthophyllite, crocidolite, erionite, and silica particles in the environment, either as a result of natural comminution of rocks, mining or other activities, are inevitable unless particular care is taken.
Complete characterization and identification of minerals in dust form are problem and lacking in air and tissue samples in Turkey. There is no fiber burden study of lungs. In addition to fiber type, dose, size and shape factors, analytical handicaps and analytical errors must be taken into consideration. For example, lung burden studies indicates that chrysotile is often inhaled as a shorter fiber than amphiboles and it is very difficult to identify chrysotile fibers in the tissue samples under optical microscope because of their smaller size. It is also very difficult to observe through electron microscope because of its beam sensitivity. Analysts tend to analyze fibers, which are more stable under beam conditions. Therefore, in a tissue with both tremolite and chrysotile, it is possible to make misjudgement unless fibers are identified individually. Chrysotile is also known to split apart longitudinally and dissolve in the lungs, whereas amphibole remains in the lungs for years without significant dissolution. For laboratory experiments, it is hypothetical that a chrysotile fiber of 1mm in diameter would completely dissolve in the human lung in 9±4.5 months.
Another problem is the form of a mineral and identification of the mineral. Tremolite, for example, occurs naturally in three distinct morphological forms or mineral habits. It may occur as asbestos, splintery fibers, or in massive crystalline deposits. Any mechanical manipulation of asbestos rocks rapidly produce many long, thin fibres/fibrils. Asbestos fibrils are easily separable, because of translocation along a twin plane, which produces a much reduced cohesion. Other defects in the structure are thought to contribute to this property. A lot of data has accumulated, which suggest that amphibole asbestos, and its non-asbestos analoques, possess very different biological potential. Selective inhalation of the particles with different weight, density, size and shape in such an environment may be another factor to consider.
In countries such as Turkey with high levels of durable mineral dust especially in fiber form in the environment, either as a result of natural comminution of rocks, mining or other activities-building with fiber-rich stone or painting houses with fiber-rich stucco, considerable environmental exposure is inevitable unless particular care is taken. If this is not performed properly, then the cumulative fiber doses experienced by the exposed population will be associated with an increased in mortality.
