Crystalline silica

Surface silanols as key descriptor of the silica hazard – Experimental validation

The variability of quartz hazard stands as one of the most puzzling issues in particle toxicology. However, a few gaps are still present in the physico-chemical determinants and cellular pathways involved in the mechanisms of silica pathogenicity (Donaldson & Borm, 1998; Pavan & Fubini, 2017). In our recent investigations, we produced quartz crystals of respirable size, exposing intact crystal faces, which did not show a biological reactivity in a series of toxicologically relevant tests (Pastero et al., 2016; Turci et al., 2016). Mechanical grinding of these unique crystal samples largely increased their activity. By combining the knowledge acquired with these synthetic quartz crystals and with a large set of silica samples (both amorphous and crystalline) from previous studies (Pavan et al., 2013; Pavan et al., 2014; Pavan et al., 2017), we newly propose silica surfaces characterized by heterogeneous and disorganized silanol patterns available for H-bonding with external molecules, such as after fracturing, as the peculiar surfaces that can promote membrane damage and inflammation, a process at the origin of silica-related diseases. We hypothesize that characterizing these specific silanols through physico-chemical and in vitro analyses will allow identifying the pathogenic activity of silica materials. In this sense, the project aims to develop a set of assays to identify and predict the respiratory hazard of quartz particles based on the analysis of silanol distribution and to validate this approach in vivo.

Read more

A cooperative project of UCL, UniTO - funded by EUROSIL


Our bibliography on the subject:


Pavan et al., 2013 (DOI: 10.1021/tx400105f)
Pavan et al., 2014 (DOI: 10.1186/s12989-014-0076-y)
Pastero et al., 2016 (DOI: 10.1021/acs.cgd.6b00183)
Pavan et al., 2016 (DOI: 10.1093/toxsci/kfw101)
Turci et al., 2016  (DOI: 10.1186/s12989-016-0136-6)
Pavan & Fubini, 2017 (DOI: 10.1021/acs.chemrestox.6b00409)
Pavan et al., 2017 (DOI: 10.1016/j.colsurfb.2017.06.012)

Role of cristallinity in the silica toxicity

Silica related diseases have usually been associated with exposure to dusts generated by some crystalline silica polymorphs. As silicosis and lung cancer are also found among workers exposed to an amorphous silica form, incorrect named “quartz glass”, the question arises of whether crystallinity is the prerequisite feature that makes a silica dust toxic. A combined study on physico-chemical properties, in vitro cellular and in vivo tests by the Centre may evidence a possible hazard for silicosis and lung cancer in workers exposed to an amorphous silica form.

Our bibliography on the subject:

Ghiazza et al, 2010 (DOI 10.1021/tx900369x)


Diatomaceous earth

Diatomaceous earth obtained by processing natural fossil diatom deposits, are the major silica source on earth. The product mined from the deposits, mostly amorphous, before being commercialized undergoes a complex processing procedure which the main step converts amorphous diatomaceous earth into cristobalite (crystalline). The role of the Centre is to clarify the conditions in which the transformation to crystalline silica occurs, the modification of surface properties and cellular responses occurs at the dust and the possible implication of such modifications in silica toxicity.

Our bibliography on the subject:

Elias et al, 2000 (DOI 10.1016/S0887-2333(00)00039-4)
Elias et al, 2002 (DOI 10.1080/00984100290071360)
Elias et al, 2006 (DOI 10.1093/toxsci/kfj177)
Ghiazza et al, 2009 (DOI 10.1021/tx800270g)


Toxicity of different silica polymorphs

Silica is the term to describe different minerals with the same chemical composition and so the same chemical formula: in fact, silica consists of crystalline (polymorphs) and amorphous specimens. Among the silica polymorphs the degree of pathogenicity depends upon several physicochemical properties, mostly determined by the “origin” and the history of the particulate. The aim of the Centre is to evaluate the different surface properties of polymorphs implicated in the different pathogenicity.

Our bibliography on the subject:

Cerrato et al, 1995
Fubini et al, 1999 (DOI 10.1021/tx980261a)
Fenoglio et al, 2000 (DOI 10.1039/JM9950501935)


Evaluation of surface properties of quartz involved in silica toxicity

The inhalation of crystalline silica causes silicosis, lung cancer, autoimmune diseases and renal pathologies. Several properties have been recognized to influence the biological response towards silica particles (e.g. particle size and shape, hydrophilic character of the surface, the generation of free radical by particles, presence of metal impurities) causing a high variability in silica toxicity of different sources of quartz. The physico-chemical tests performed by our Centre, combined with bio-chemical cellular tests may help to highlights the role played by each property of the silica particles in the mechanism of pathogenicity.

Our bibliography on the subject:

Fubini et al, 2004 (DOI 10.1078/1438-4639-00277)
Bruch et al, 2004 (DOI 10.1078/1438-4639-00278 )
Cakmak et al, 2004(DOI 10.1078/1438-4639-00276)