Release of Si from silicon, a ferrosilicon (FeSi) alloy and a synthetic silicate mineral in simulated biological media.

Gunilla Herting,Tao Jiang,Inger Odnevall Wallinder,Carin Sjöstedt,Christophe Egles

doi:10.1371/journal.pone.0107668

Abstract

Unique quantitative bioaccessibility data has been generated, and the influence of surface/material and test media characteristics on the elemental release process were assessed for silicon containing materials in specific synthetic body fluids at certain time periods at a fixed loading. The metal release test protocol, elaborated by the KTH team, has previously been used for classification, ranking, and screening of different alloys and metals. Time resolved elemental release of Si, Fe and Al from particles, sized less than 50 µm, of two grades of metallurgical silicon (high purity silicon, SiHG, low purity silicon, SiLG), an alloy (ferrosilicon, FeSi) and a mineral (aluminium silicate, AlSi) has been investigated in synthetic body fluids of varying pH, composition and complexation capacity, simple models of for example dermal contact and digestion scenarios. Individual methods for analysis of released Si (as silicic acid, Si(OH)4) in synthetic body fluids using GF-AAS were developed for each fluid including optimisation of solution pH and graphite furnace parameters. The release of Si from the two metallurgical silicon grades was strongly dependent on both pH and media composition with the highest release in pH neutral media. No similar effect was observed for the FeSi alloy or the aluminium silicate mineral. Surface adsorption of phosphate and lactic acid were believed to hinder the release of Si whereas the presence of citric acid enhanced the release as a result of surface complexation. An increased presence of Al and Fe in the material (low purity metalloid, alloy or mineral) resulted in a reduced release of Si in pH neutral media. The release of Si was enhanced for all materials with Al at their outermost surface in acetic media.

Highlights

Silicon is the second most abundant element found in the Earths crust and is commonly found as silica (SiO2) or as silicates, the latter being the most abundant mineral group [1,2].The silicon surface is, unless modified, covered with a few nm thick layer of amorphous silica [3,4]
Release data after 168 h of exposure will in the following be used to illustrate these effects as the short-time periods in many cases reveal released amounts of Si close to, or below the limit of detection for the given fluid, exemplified for SiHG in phosphate buffered saline (PBS), Figure 3
To assess the influence of test media pH on the amount of released Si, Si HG was exposed in PBS for 168 h and compared with parallel measurements in pH adjusted PBS solutions. These pH levels were selected based on acidity of artificial sweat (ASW), artificial lysosomal fluid (ALF) and gastric juice (GST)

Summary

Introduction

Silicon is the second most abundant element found in the Earths crust and is commonly found as silica (SiO2) or as silicates, the latter being the most abundant mineral group [1,2].The silicon surface is, unless modified, covered with a few nm thick layer of amorphous silica [3,4]. Silicon possess desirable properties applicable for semiconductors and solar cells, but it is widely used in glasses, ceramics and refractory materials and as an alloying element for many steel grades and aluminium alloys. This may cause human exposures to a wide variety of silicon containing powder particles at e.g. occupational settings. Airborne particles are associated with adverse effects on human health [4] and several studies using both in-vitro and invivo approaches have been performed to evaluate how humans may be affected by for example silica and asbestos [6,7,8,9,10,11]. Only few studies have addressed silica dissolution in synthetic biological solutions [4,11]

Methods

Results

Conclusion