Crystal-chemistry and reactivity of fibrous amphiboles of environmental and health interest

The present study is devoted to the investigation of amphibole fibers by means of a well tested multi-analytical approach. The studied speciments are tremolite fibers from ophiolitic outcrops at different Italian localities such as (from north to south): 1) Ala di Stura (Lanzo Valley, Piedmont); 2) Mt. Rufeno (Acquapendente, Latium); 3) Castelluccio Superiore (Potenza, Basilicata); 4) S. Mango (Catanzaro, Calabria). A sample of fibrous tremolite from the ophiolite complex outcropping in Montgomery County, Maryland (USA) was also studied. In addition, the nonregulated fibrous amphiboles from Biancavilla (Catania, Sicily) and Libby (Montana, USA) are studied for comparison. The detailed crystal chemical characterization was carried out by combining Inductively Coupled Plasma-Mass (ICP-MS) spectrometry, Electron Microprobe Analysis (EMPA), Scanning Electron Microscopy (SEM) with microanalysis system, parallel-beam X-Ray Powder Diffraction (XRPD), 57Fe Mössbauer spectroscopy (MS) and Fourier-Trasform Infra-Red (FT-IR) spectroscopy. Beside the mineralogical characterization, the surface chemistry and surface reactivity of some samples have been also investigated. The surface chemistry of the fibers was studied by X-Ray Photoelectron Spectroscopy (XPS) with specific attention to the surface iron content and its oxidation state. Electron Paramagnetic Resonance (EPR) Spectroscopy was used to characterize the HO° hydroxyl radicals and the measurement of their absolute concentration. In addition, tests of lipid peroxidation in the presence of hydrogen peroxide were performed to identify and distinguish their reactivity, and the degradation of linolenic acid in conditions similar to those found in pulmonary alveoli was monitored. The products of degradation of linolenic acid were studied by UV-visible spectroscopy. The surface chemistry and the reactivity of a sample of crocidolite UICC (Union Internationale contre le Cancer, Johannesburg, South Africa) and a sample of calcite (Iceland spar variety) were also investigated as positive and negative references, respectively. Finally, full characterization of fibrous amphiboles (morphology, crystal chemistry, crystal structure, cation site partitioning, Fe3+/Fetot ratio of the bulk and surface, surface 13 chemistry and reactivity) was coupled with cytotoxicity tests in vitro (MTT test on A 559 and MeT- 5A cells) performed on the same samples. The aim is to better understand the relationships between mineralogical features and biological activity in order to shed new light on the chemical, molecular and toxic-chemical processes in the interaction between fiber and organic environment. This work required the use of several complementary disciplines from mineralogy to chemistry and biology. Therefore, the collaboration between the Sapienza University of Rome and the University of Pierre et Marie Curie of Paris VI was the underlying framework of such a challenging and interdisciplinary work.

La caratterizzazione cristallochimica di fibre minerali, in particolar modo di anfiboli fibrosi, risulta di grande interesse, non solo per l’aspetto mineralogico, ma anche e soprattutto per quello ambientale e sanitario. I minerali fibrosi si presentano nelle rocce ospiti solitamente associati in fasci più o meno compatti, anche se in alcuni casi possono presentarsi sciolti nei materiali geologici, come per es. nel recente rinvenimento dell’anfibolo fluoro-edenite nei prodotti vulcanici di Biancavilla, CT, nei quali il minerale fibroso si presenta disperso nel materiale fine che lo ospita, e dal quale risulta alquanto difficoltosa la sua estrazione e separazione, necessaria per le successive analisi mineralogiche (Gianfagna et al., 2003; Gianfagna et al., 2007). Recenti studi a carattere ambientale, epidemiologico e tossicologico nell’area di Biancavilla hanno evidenziato che l’interazione tra la fibra minerale e l’ambiente organico è risultata strettamente correlata sia alla forma che alla cristallochimica delle fibre anfiboliche che entrano in contatto con il mezzo biologico (Paoletti et al., 2000; Comba et al., 2003; Soffritti et al. 2004). Anche se in questi ultimi anni particolare attenzione è stata rivolta alla cristallochimica degli anfiboli, sia prismatici che fibrosi, le difficoltà oggettive esistenti per lo studio mineralogico e strutturale delle varietà fibrose non hanno permesso di ottenere ad oggi una loro completa e dettagliata definizione in termini cristallochimici. Il presente dottorato di ricerca si prefigge quindi di studiare dal punto di vista mineralogico e cristallochimico le varietà fibrose di alcuni anfiboli presenti per la maggior parte in aree in cui si è manifestata maggiormente in passato ed è tutt’ora presente, la problematica di inquinamento ambientale da esposizione naturale a fibre.