Erionite, Offretite and Stellerite: Solubility Assay

Erionite is a well known carcinogenic fibrous zeolite being one of the most carcinogenic mineral fibre (IARC, 1987). In the last years other fibrous zeolites, such as offretite and ferrierite, assumed a growing interest in the scientific community, because of their probably carcinogenic effects to human after inhalation (Mattioli et al., 2018; Gualtieri et al., 2018).

The toxicity of these minerals is mainly defined by two important parameters: biodurability and biopersistence. Solubility plays a key role on these parameters; however, to the best of our knowledge, the experimental determination of the solubility of erionite and offretite is still missing. The lack of these data for natural zeolites, even in the most simple system (i.e. water), represents a severe limitation for the understanding of the complex interaction with the biological environments. The aims of this study is to be a starting point for further detailed studies on the dissolution kinetics of zeolites. Our experimental setup for low temperature kinetic studies could allows to figure out (I) the behaviour in pure water and then (II) the effect of inorganic and organic additives (e.g. in Simulated Lung Fluids). The assessment of the individual role of each component is fundamental to better understand the observed processes, and could be a starting point for the comprehension of the risks associated to human health.

Natural samples of erionite, offretite and stellerite (more abundant zeolite used as reference material) were used to perform dissolution experiments, at 25° C, to assess their aqueous solubility under the effect of atmospheric CO₂ concentration.

To obtain a relatively homogeneous crystal particle in the range 64 µm - 250 µm, the natural crystals were ground and sieved. The selected fraction was added to ultrapure H₂O (previously equilibrated with air for 30 minutes under stirring, i.e. in equilibrium with atmospheric CO₂ at pH 5). The dissolution process was followed over time with a conductivity probe equipped on a Metrohm OMNIS system. After several hours (days) under vigorous stirring (a floating stirrer was used to avoid a milling effect on the crystals), the samples were filtrated and the amount of Ca, Na, K, Mg, Al and Si was determined by ICP-OES (Agilent Varian, 700 ES). The powders were characterized before and after the interaction period. X-ray powder diffraction was used for the mineralogical characterization. The morphological characterization of the grains and the determination of the elemental formula were obtained by means of SEM-EDS and EMPA, respectively.

 

IARC. 1987. IARC Monographs on the Evaluation of the Carcinogenic Risk to Humans; Overall Eval. Carcinog. Updating IARC Monographs Vol. 1 to 42; IARC: Lyon, France.

Mattioli, M., Giordani, M., Arcangeli, P., Valentini, L., Boscardin, M., Pacella, A. and Ballirano P. 2018. Prismatic to Asbestiform Offretite from Northern Italy: Occurrence, Morphology and Crystal-Chemistry of a New Potentially Hazardous Zeolite. Minerals, 8, 69.

Gualtieri, A.F., Gandolfi, N.B., Passaglia, E., Pollastri, S., Mattioli, M., Giordani, M., Ottaviani, M.F. Cangiotti, M., ... and Gualtieri, M. L. 2018. Is fibrous ferrierite a potential health hazard? Characterization and comparison with fibrous erionite. American Mineralogist, 103(7), 1044-1055.