Ferrosilicon - reaction mass of iron and iron disilicide and iron silicide and silicon

Endpoint summary

Description of key information

The effects of repeated exposure to silicon particles were recently investigated in a subchronic inhalation study. The results showed no signs of systemic toxicity. The main findings were very mild, local inflammatory effects observed in the lungs and lung-associated lymph nodes. No severe exposure-related effects were observed. No other studies on repeated dose toxicity of silicon were available. 
Repeated dose toxicity data on synthetic amorphous silica and calcium silicate show that the silicon ion does not cause systemic target organ toxicity after oral exposure. The comparative in vitro data on the dissolution kinetics of ferrosilicon, and the read-across materials silicon and synthetic amorphous silica in different artificial biological fluids show that the dissolution from ferrosilicon particles in vitro is not markedly different from that of silicon or synthetic amorphous silica. Based on read-across, no systemic toxicity is expected from oral exposure to ferrosilicon.  No indications of endocrine disrupting effects have been observed.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Quality of whole database:

No studies available on ferrosilicon. Read-across to amorphous silicon dioxide and silicates is justified, and robust studies available on those substances.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

16 mg/m³

Study duration:

subchronic

Species:

rat

Quality of whole database:

No studies available on ferrosilicon. Robust guideline study on silicon available. Read-across justified.

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

4 mg/m³

Study duration:

subchronic

Species:

rat

Quality of whole database:

No studies available on ferrosilicon. Robust guideline study on silicon available. Read-across justified.

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No repeated dose studies were available on ferrosilicon, and therefore read-across to silicon, synthetic amorphous silica and silicates was applied.

The comparative in vitro data on the dissolution kinetics of ferrosilicon, silicon and synthetic amorphous silica in different artificial biological fluids show that the dissolution of silicon does not differ markedly. Therefore, the bioavailabity of silicon from ferrosilicon particles is likely to be similar or lower than that of silicon or synthetic amorphous silica.

A detailed description of the justifications for read-across is available in Section 13 of the Iuclid dossier.

Repeated dose systemic toxicity

No systemic effects were observed after subchronic exposure of rats to silicon particles by inhalation. Furthermore, repeated dose toxicity data on synthetic amorphous silica show that the silicon ion does not cause systemic target organ toxicity after ingestion. Also, repeated dose toxicity data on calcium silicate do not show any systemic toxicity. Calcium silicate can be used as a read-across substance for FeSi since it is a sparingly soluble silicon compound. Thus, based on read-across to silicon, synthetic amorphous silica and calcium silicate, no systemic toxicity is expected from oral exposure to ferrosilicon. 

Repeated dose local toxicity

No repeated dose studies were available on ferrosilicon. The main target organs for exposure to ferrosilicon by inhalation are the lungs. Repeated exposure to silicon particles in the alveolar size range at 16 mg/m3 resulted in very mild local inflammatory effects in the lungs and lung-associated lymph nodes. No statistically significant effects were observed at lower exposure doses.

Two epidemiological studies among the workers exposed to synthetic amorphous silica did not show any effects on lung function (Wilson et al. 1979; Choudat et al. 1990). Recent epidemiological studies from the silicon/ferrosilicon industry suggest the increased prevalence of COPD and decline in lung function (FEV1) of the exposed workers. The latest studies by Johnsen and co-workers (e.g., Johnsen et al. 2010) correlate these with cumulative dust exposure. The effect was seen both in FeSi/Si and FeMn/SiMn/FeCr plants. Increasing evidence has accumulated showing that COPD may be related to workplace exposure to dusts, fumes and gases in general. It has been estimated that for COPD a population attributable risk of 15-20% is caused by occupational dusts/fumes. Therefore, the increased risk of COPD reported in the metallurgical industry is likely to be a general dust/fume exposure-related phenomenon rather than a specific effect of silicon or silica fumes formed during the process. Since ferrosilicon particles are only a minor component of these dusts present in silicon/ferrosilicon factories, no firm conclusions on the inhalation toxicity of ferrosilicon can be made based on the epidemiological studies. However, colclusions can be drawn from read-across to silicon and synthetic amorphous silica.

Barium is known to cause baritosis, which is a form of benign pneumoconiosis causing no effects on lung function. Strontium and barium, even as soluble compounds, have caused systemic toxicity only at high dose levels in repeated dose/chronic toxicity studies.

No indications of endocrine disrupting effects have been observed in any of the studies.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Read-across to guideline study performed with synthetic amorphous silica (silica gel).

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
Read-across to OECD 413 guideline study performed with silicon.

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:
Read-across to OECD 413 guideline study performed with silicon.

Justification for classification or non-classification

Ferrosilicon has not been tested for repeated dose toxicity, and therefore read-across to silicon, amorphous silica and silicates was applied.

In a 90-day inhalation toxicity study with silicon particles, no systemic effects were observed. Very slight inflammatory effects in the lungs and lung-associated lymph nodes were reported at the highest dose tested (16 mg/m3). These findings were considered not to support classification of silicon since 1) the effects were rated as very slight in severity, 2) were only observed at a dose leading to increased retention of particles in the lungs (moderate lung overload), and 3) were clearly distinct from the severe progressive inflammatory effects observed with quartz (1 mg/m3). The findings following inhalation exposure to silicon particles are likely to be predominantly caused by general, non-substance-specific, effects of poorly soluble particles at lung burdens exceeding the capacity of the macrophage-mediated alveolar clearance.

Calcium silicate, which has also been found in the surface of ferrosilicon, has not caused any toxic effects after 12 months of inhalation exposure of rats at dose levels of 10 mg/m³.

Oral studies on amorphous silica show a lack of systemic toxicity. Also other components, released from some grades of ferrosilicon (strontium in the case of FeSiSr and barium in the case of FeSiBa) have shown systemic toxicity in repeated/long term toxicity studies only at high dose levels (>100 mg/kg/day).

Based on weight-of-evidence and taking into account the epidemiological data, data on the toxicity of silicon, amorphous silica and calcium silicate do not raise concerns about repeated dose toxicity of ferrosilicon.

Conclusion: No classification of ferrosilicon is suggested.