This project is aimed at investigating both the surface and bulk modifications occurring on fibrous erionite, a Group 1 Human-Carcinogen, during leaching in a mimicked Gamble's solution (MGS) at pH of 4.5 and T = 37 °C, up to 1 month of incubation. This formulation is selected to reproduce in a simplified way the lung fluid where such fibres may persist upon inhalation. Samples will be characterized by using a multi-analytical approach: field-emission scanning electron microscopy will be employed to investigate the morphological features of both pristine and reacted fibres, inductively coupled plasma optical emission spectrometry will be used to measure the concentration of released cations, X-ray diffraction (XRD) will be applied for investigating the structural state of the fibres after incubation. Our results are potentially crucial at disclosing, under such experimental conditions, the process of leaching of erionite-K fibres and should provide, as well, an estimation of erionite biodurability. This piece of information is of relevance considering the primary role played by biodurability in inducing pathogenicity. Besides, the ions released by erionite when immersed in MGS may trigger biological effects, because, as example, Ca ions are able to induce opening of the permeability transition pore of the inner membrane leading to a possible cytotoxic effect due to the release of apoptotic factors normally localized in the mitochondrial intermembrane space, whereas Mg ions may have different effects on lipid packing and membrane permeability.
In this study we plan to investigate, by applying a multianalytical approach, the chemical structural modifications occurring on fibrous erionite during incubation in MGS at pH of 4.5 and T = 37 °C, up to 1 month of incubation. Our results are expected to disclose, under such experimental conditions, the process of leaching of erionite-K fibres which is expected to produce an ionic-exchange process of the extra-framework cations by Na+ ions present in the solution, leading to a significant modification of the chemical composition of erionite (potentially passing from erionite-K to erionite-Na). The interaction between erionite and MGS could produce a surface amorphous layer similarly to what observed in the case of SLF. The expected results should allow a more accurate estimation of erionite bio-durability. This piece of information is of relevance considering the primary role played by bio-durability and bio-persistence in inducing pathogenicity. Besides, the ions released by erionite when immersed in MGS may trigger biological effects, because Ca ions are able to induce opening of the permeability transition pore of the inner membrane leading to a possible cytotoxic effect due to the release of apoptotic factors normally localized in the mitochondrial intermembrane space, whereas Mg ions may have different effects on lipid packing and membrane permeability. The multidisciplinary approach proposed in this research project is perfectly suited to deal with tangled issues like those involving fibrous erionite. On this basis, it is exportable to the study of other mineral fibres and inorganic dusts of environmental and health interest. The description of the dissolution process might provide useful information for interpreting the chemical reactivity of fibrous erionite, sheding new light on the comprehension of its toxic action. This will allow the mechanism related to the carcinogenic action of erionite to be understood in greater detail by the biomedical community. The mesothelioma cases identified in North America led to consider the erionite natural occurrence as an emerging national public health concern. Notably, the occurrence of fibrous erionite was also reported in the North of Italy. However, epidemiological studies are still extremely scarce and no mesothelioma cases have been evidenced so far. Further advances to the understanding of the mechanisms by which toxicity of fibrous erionite originate are of significant importance in developing plans designed to the protection of the public health. Besides, results from the present research could be integrated with those previously obtained, using a similar multi-disciplinary approach, by the research group on amphibole asbestos of environmental and health relevance. The comparison will disclose the similarities and differences between fibrous erionite and amphibole asbestos physico-chemical parameters, including their toxicity potential. Notably, regulations on erionite are not present in the United States and in Italy so far and, therefore, this work it is expected to be an invaluable scientific support for the policy makers.