Biosolubility of high temperature insulation wools in simulated lung fluids

Abstract

Objective Biosolubility is an important parameter in the understanding of mechanisms involved in pulmonary toxicity of fibrous materials. It can be studied in vitro using models of simulated lung fluids and observing the loss of structural molecules, expressed as dissolution constant (K dis ). The aim of this paper was the study of dissolution behaviour of four wools belonging to high temperature insulation wools (HTIW) in saline solutions simulating lung fluids. Methods Four HTIW were studied in saline solutions at pH 7.4 (representative of the extracellular environment) and 4.5 (representative of the intracellular conditions): refractory ceramic fibers (RCF), two alkaline earth silicate wools (AES1 and AES2 with high calcium and magnesium content respectively), and polycrystalline wools (PCW). Size, morphological and chemical changes of fibers were observed by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Results RCF, AES2 and PCW did not show statistically significant diameter changes. AES1 size distribution shifted to a larger mean diameter suggesting that through dissolution there was a preferential loss of thin fibers at acid pH after 14 days of treatment. Both AES wools showed selective leaching of alkali/alkali earth oxides (incongruent dissolution) at pH 7.4: a fast and extensive selective leaching of calcium for AES1 with complete dissolution of fibers already after 14 days of treatment and a moderate selective leaching of magnesium for AES2. PCW showed some transversal breakage of the fibers in both pH environments (low congruent dissolution). For RCF, the treatment produced uncorroded fibers in both pH environments without chemical changes and fiber fragmentation (no dissolution). The estimated K dis at physiological pH followed the sequence: AES1 > AES2 > PCW > RCF. All wools had a low K dis at acid pH suggesting a low dissolution rate of short fibers. Conclusion The leaching process and transverse fragmentation play an important role in the biopersistence mechanisms and pathogenicity of fibers and the K dis estimate is undoubtedly useful as a preliminary toxicological screening of fibers, especially for developing fibers.

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).…”

“…For example, Fe dissolution was minimal in the neutral Gamble's solution and high in acidic AM culture (Luoto et al 1994). Cannizzaro et al (2019) assessed RCF and two alkaline earth silicate (AES) wools incubated in Gamble's solution at pH 7.4 and a lowered pH of 4.5. RCF were found to be unaffected during the 14-day exposure of either fluid.…”

“…For AES, the acid solution was found to cause dissolution of thin fibres only, in neutral solutions dissolution patterns were specific to fibre composition. 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).…”

“…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.…”

“…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.…”