Assessing the bioactivity of crystalline silica in heated high-temperature insulation wools

Abstract

High-Temperature Insulation Wools (HTIW), such as alumino silicate wools (Refractory Ceramic Fibers) and Alkaline Earth Silicate wools, are used in high-temperature industries for thermal insulation. These materials have an amorphous glass-like structure. In some applications, exposure to high temperatures causes devitrification resulting in the formation of crystalline species including crystalline silica. The formation of this potentially carcinogenic material raises safety concerns regarding after-use handling and disposal. This study aims to determine whether cristobalite formed in HTIW is bioactive in vitro. Mouse macrophage (J774A.1) and human alveolar epithelial (A549) cell lines were exposed to pristine HTIW of different compositions, and corresponding heat-treated samples. Cell death, cytokine release, and reactive oxygen species (ROS) formation were assessed in both cell types. Cell responses to aluminum lactate-coated fibers were assessed to determine if responses were caused by crystalline silica. DQ12 α-quartz was used as positive control, and TiO2 as negative control. HTIW did not induce cell death or intracellular ROS, and their ability to induce pro-inflammatory mediator release was low. In contrast, DQ12 induced cytotoxicity, a strong pro-inflammatory response and ROS generation. The modest pro-inflammatory mediator responses of HTIW did not always coincide with the formation of cristobalite in heated fibers; therefore, we cannot confirm that devitrification of HTIW results in bioactive cristobalite in vitro. In conclusion, the biological responses to HTIW observed were not attributable to a single physicochemical characteristic; instead, a combination of physicochemical characteristics (cristobalite content, fiber chemistry, dimensions and material solubility) appear to contribute to induction of cellular responses.

Simulated biological fluids – a systematic review of their biological relevance and use in relation to inhalation toxicology of particles and fibres

“…Unlike RCF, AES have been shown to demonstrate a low biopersistence in vivo (Bernstein et al 1996), due to the presence of alkaline earth oxides, such as Ca and Mg (Brown and Harrison 2012). This behaviour has been reproduced using in vitro dissolution studies involving modified Gamble's solution (Boyles et al 2018;Cannizzaro et al 2019).…”

“…AES containing CaO dissolved rapidly and completely within 14 days through leaching of Si and Ca [as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES)], while fibres not containing CaO were shown to release moderate levels of Mg and Si (Cannizzaro et al 2019). In a study which examined a similar panel of high-temperature insulation wools (HTIW), Boyles et al (2018) Cannizzaro et al (2019). Still based on Gamble's solution, the Mg-and Ca-contributing salts had been excluded, to improve detection of low level releases from the fibres (Boyles et al 2018), this may have contributed to the differences observed between these two studies.…”

“…In a study which examined a similar panel of high-temperature insulation wools (HTIW), Boyles et al (2018) Cannizzaro et al (2019). Still based on Gamble's solution, the Mg-and Ca-contributing salts had been excluded, to improve detection of low level releases from the fibres (Boyles et al 2018), this may have contributed to the differences observed between these two studies.…”

“…also demonstrated a high dissolution of AES when compared to RCF Cannizzaro et al (2019). tested calcium magnesium silicate wool (CMS) and magnesium silicate wool (MS), whereasBoyles et al (2018) tested calcium silicate wool (CaS) in addition to CMS and MS. Boyles et al found dissolution to be greater in pH 4.5 solutions compared to pH 7.4 solutions, and fibres containing Mg and Ca were shown to release these components at almost equal levels. The dissolution tests conducted by Boyles et al (2018) used a fluid composition which differed from that of…”

In vitro assessment of the pulmonary toxicity of particulate matter emitted during haze events in Chiang Mai, Thailand via investigation of macrophage responses

“…In this study, the murine J774A.1 macrophage cell line was used as a surrogate of alveolar macrophages as they have been extensively used in in vitro investigations assessing the pulmonary toxicity of various particles (e.g. Brown et al 2004, Zhou and Kobzik 2007, Rothen-Rutishauser et al 2010, Clift et al 2011, Yue et al 2012, Ma et al 2015, Boyles et al 2018. All particles were evaluated for their ability to induce cytotoxicity, changes in cellular morphology and pro-inflammatory responses in macrophages in vitro as a measure of their toxicity.…”