Biosolubility of high temperature insulation wools in simulated lung fluids

Annapaola Cannizzaro,Elena Barrese,Federica Angelosanto,Antonella Campopiano

doi:10.1186/s12995-019-0235-z

Abstract

ObjectiveBiosolubility 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 (Kdis). 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.MethodsFour 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).ResultsRCF, 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 Kdis at physiological pH followed the sequence: AES1 > AES2 > PCW > RCF. All wools had a low Kdis at acid pH suggesting a low dissolution rate of short fibers.ConclusionThe leaching process and transverse fragmentation play an important role in the biopersistence mechanisms and pathogenicity of fibers and the Kdis estimate is undoubtedly useful as a preliminary toxicological screening of fibers, especially for developing fibers.

Highlights

Asbestos was used widely in Italy until its use was banned in 1992 leading to the development of other fibrous materials [1,2,3]
We studied the behaviour of four wools belonging to high temperature insulation wools (HTIW) (RCF, two types of alkaline earth silicate (AES) and polycrystalline wools (PCW)) in saline solution simulating physiological fluids
Three amorphous wools: refractory ceramic fibers (RCF), a traditional wool used for very high temperature insulation applications and two AES wools that differ in the chemical composition

Summary

Introduction

Asbestos was used widely in Italy until its use was banned in 1992 leading to the development of other fibrous materials [1,2,3]. RCF fibers have been classified by the International Agency for Research on cancer (IARC) as possibly carcinogenic to humans (Group 2B) [5]. AES wools are materials that are designed to have low biopersistence and low hazardousness [3, 6]. Fibers can be designed to be inherently less hazardous. The development of alkaline earth silicate (AES) wools, with alkaline oxides and alkali earth oxide content less or equal to 18% by weight, determined the birth of a new class of fibers a low biopersistence. AES wools are materials that have been designed to be rapidly cleared from lung tissue [2]

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Conclusion