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There is no specific data on the in vivo toxicokinetics of ferrosilicon. However, in vitro studies on the release of the different ferrosilicon components from ferrosilicon particles in artificial biological fluids give us information on bioaccessibility, and therefore, also the possible bioavailability of the different ferrosilicon components. These dissolution studies have been made with different grades of ferrosilicon. Silicon is the main constituent in these tested ferrosilicon materials, being present in bulk material at concentrations of 15-76% (w/w %). These studies show that the release of silicon from ferrosilicon is low. When compared to synthetic amorphous silica, depending on the solution used, the silicon is released at similar or lower amounts from FeSi -materials than from synthetic amorphous silica particles. Thus, the bioavailability of silicon from ferrosilicon is likely to be similar or lower than from amorphous silica.

The release of iron from ferrosilicon alloy is restricted by the surface oxide layer. Regardless of the iron content of 20-84% of tested materials, the iron release measured, e.g., in FeSiSr was <0.3% (w/w %) of loaded material. This means that only 1% or less of the iron present in the bulk sample was dissolved. This resembles the release of iron from synthetic amorphous silica. Thus, even if FeSi contains significantly more iron than synthetic amorphous silica, its iron release is so low that it is unlikely to affect the toxicological properties of ferrosilicon, and read-across from synthetic amorphous silica is justified.

The release of other elements was also limited. FeSiBa samples containing 1.65 wt% of aluminium released at maximum 216μg Al/l in GST. This is, however, very close to the level of aluminium released from synthetic amorphous silica particles (128μg Al/l in GST, Herting et al.2009: report on synthetic amorphous silica). Also the release of zirconium from FeSiZr was very low: the maximum release was limited to 0.4μg Zr/l in GST, which was less than 0.01% of the zirconium present in the bulk sample (bulk content approximately 5%). Usually zirconium levels in test fluids remained below detection limits. Other elements, which were sparingly released, although present at significant bulk concentrations, included titanium, copper, manganese and zinc. Copper release from different grades of FeSi particles in PBS and GST varied from non-detectable to maximum 70μg/l, levels mostly staying below 10μg/l. Synthetic amorphous silica release copper 3μg/l in GST. Manganese is released from FeSi at levels remaining usually <5μg/l, the maximum release being 18.8μg/l. This is not significantly different from the release of manganese from synthetic amorphous silica particles (3.5μg/l in GST). Also titanium release from ferrosilicon is at non-detectable level. These results show that health hazards of ferrosilicon can be primarily based on health hazard data on silicon and synthetic amorphous silica. Since release of silicon, iron, aluminium, copper, manganese, titanium and zirconium from ferrosilicon and synthetic amorphous silica are similar, synthetic amorphous silica can be used for read-across to cover the toxicity of these components. However, strontium and barium are released from ferrosilicon particles containing Sr and Ba at higher levels than from synthetic amorphous silica. The impact of these elements on the toxicity should be further considered in the case of different end-points. Due to the poor solubility and low dissolution of metal components of ferrosilicon, no in vivo studies on the toxicokinetics of ferrosilicon are suggested. Based on in vitro dissolution data in artificial body fluids, hazard assessment of ferrosilicon can be based on the toxicity of silicon and silica, taking into account the impact of slightly soluble strontium and barium.

A subchronic inhalation study with silicon particles (MMAD 2.6 µm) was performed in Wistar rats according to OECD 413 (Fraunhofer ITEM 2014). The doses used in the test were 1, 4 and 16 mg/m3of silicon. The results showed that subchronic exposure by inhalation resulted in an overload effect in rat lungs at the highest dose level (16 mg/m3). The calculated half-times for silicon after exposure at 16 mg/m3were 128 days for male and 119 days for female rats.

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