Mineralogical study of the fibrous zeolites erionite and offretite and hazard assessment

The exposure of erionite fibres to humans has been unambiguously linked to malignant mesothelio-ma, and in vivo studies have demonstrated that, at present, erionite is the most carcinogenic mineral in the world. Recently, a growing concern has developed regarding the potential risks associated with environmental and occupational exposures to erionite in different Countries, such as Turkey, U.S.A., Mexico and Iran. Despite of the great number of researches, the relationships among miner-alogical features and biological activity of erionite have not been fully understood and there are no systematic studies on the distribution of erionite or other similar fibrous zeolites in the environment. Moreover, there is another zeolite, named offretite, which is closely related both structurally and chemically to erionite. Despite commonly occurring as prisms, offretite has also been found under asbestiform habit, meaning that the morphology of its crystals has not yet been fully known and many mineralogical aspects are still to be discovered. Due to these similarities and to the possible in-tergrowth, the distinction between erionite and offretite can be hampered. To date, there are no studies regarding a potentially hazard of offretite fibers and it is unclear whether the mineralogical distinction between erionite and offretite has any health implications. The gap of knowledge of the fibrous zeolites erionite and offretite has been the starting point for the development of the present PhD project. A multi-methodological approach, based on field investigation, morphological characterization, SEM/EDS chemical analysis and structure refinement through X-ray powder diffraction was ap-plied to different samples of potentially carcinogenic erionite and offretite from Italy. These investi-gations were performed on representative samples with variable morphologies, ranging from pris-matic, through acicular and fibrous, to extremely fibrous asbestiform habits. In the investigated samples, fibrils of inhalable size are present. Considering that the toxicity and the carcinogenic po-tential of erionite are associated with its size parameters, together with its in vivo durability and very high surface area, most of the investigated fibers may also be potentially carcinogenic. Despite of the lack of epidemiological information on populations exposed to natural asbestiform minerals oth-er than asbestos and erionite, results acquired in the present investigation suggest that other mineral fibres of similar size, habit, and biopersistence may carry a risk for humans. Successively, morpho-chemical characterization and surface properties determinations were per-formed on a selection of different asbestiform zeolite fibers: two erionite samples (from USA and Turkey), one offretite sample (Italy) and, for comparison, one scolecite sample (India). These sam-ples have been used to carry out in-vitro experiments to assess the level of reactivity and transfor-mation that such fibers may induce to micelles and membranes in contact with them, and therefore, indirectly the possibility of leading to asbestos-related lung diseases. With this aim, specific surface area determinations coupled with EPR analysis and TEM images in the presence of model mem-branes are performed. This type of study has allowed me to obtain informations on the fiber inter-nalization in the membranes and the interactions occurring at a molecular level that mimicked the at-tack of the fibers at the cell membrane. The carcinogenicity of the zeolites may be nicely related to the structural modifications of the model membranes when interacting with these zeolite fibers. These results helped to clarify the chemical properties and the surface interacting ability of these ze-olite fibres which may be related to their carcinogenicity.