Reaction mass of calcium disilicide and calcium silicide

Endpoint summary

Description of key information

No human or experimental information is available on the repeated-dose toxicity of silicocalcium.
Read-across from amorphous silica and calcium silicate is used because the surface of silicocalcium is composed mainly of silicon and calcium rich oxides. The amounts of iron and aluminium released from the alloy do not affect the physiogical background concentrations, and their effects are negligible.
Amorphous silicon dioxide does not show systemic toxicity in oral repeated dose studies. Thus, silicon (silicic acid) released also from silicocalcium is unlikely to cause any effects. Also calcium silicate did not cause repeated dose toxicity in test animals. These facts support the conclusion that the repeated dose oral toxicity of CaSi is low.
While CaSi has not been subjected to inhalation toxicity studies, the effects of amorphous silicon dioxides have been widely studied. The respirable amorphous silica particles (MMAD <5–10 µm) have caused lung effects like inflammation, granulomatous lesions and interstitial fibrosis, which were, however, reversible. Since these effects are very much related to "general" dust effects, they might as well occur also in heavy CaSi particle exposures. Calcium silicate in a 224-day inhalation at the concentration of 10 mg/m3 did not show adverse effects in rats.
No classification is suggested because of the likely repeated dose nontoxicity of silicocalcium.

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

1.3 mg/m³

Study duration:

chronic

Species:

rat

Additional information

No human or experimental information is available on the repeated-dose toxicity of silicocalcium.

Read-across from amorphous silica and calcium silicate is used because the surface of silicocalcium is composed mainly of silicon and calcium rich oxides. Other relevant surface constituents include iron and aluminium oxides. Silicon is released from CaSi at similar or somewhat lower levels than from amorphous silicon dioxide. The release of iron from silicocalcium is very restricted and when compared to the physiological iron contents, it do not present any toxicological hazard.. Although calcium is released in significant amounts from CaSi this contribution is negligible when compared with the amounts ingested in food or water or present in tissues. Thus, amorphous silica and Ca-silicate is used for read-across in the assessment of the repeated dose toxicity of CaSi.

Oral repeated dose toxicity studies with amorphous silicon dioxide do not show systemic toxicity. Thus, silicon (silicic acid) released from silicocalcium is unlikely to cause any effects. Studies with calcium silicate have been reported: a 2-year study with rats, a 5-day sub-acute study with rats, and a 1-year study with dogs. These studies did not cause repeated dose toxicity in test animals which supports the conclusion that the repeated dose toxicity of CaSi is low.

Small amounts of aluminium are released in acidic conditions from silicocalcium in synthetic biological fluidsin vitro. The use of aluminium silicates as food additives and in cosmetics does not, however, indicate appreciable repeated-dose toxicity. In addition, the release of Al from CaSi has been detected only in very acidic fluids (gastric juice). 

While CaSi has not been subjected to inhalation toxicity studies, the effects of amorphous silicon dioxides have been widely studied. The respirable synthetic amorphous silica particles (MMAD <5–10 µm) have caused lung effects like inflammation, granulomatous lesions and interstitial fibrosis, which are, however, reversible. Since these effects are very much related to "general" dust effects, they might as well occur also in heavy CaSi particle exposures.

 

In a 224-day calcium silicate inhalation study with the concentration of 10 mg/m³no adverse effects were seen in rats.

 

Proposal on Classification

The applicability of the CLP/GHS classification on repeated dose target organ toxicity to silicocalcium was assessed.

CLP/GHS criteria classify substances as specific target organ/systemic toxicants by expert judgement on the basis of the weight of all evidence available, including the use of recommended guidance values. The choice among the two result categories depends upon the nature and severity of the observed effect(s).

In the case of silicocalcium, no specific toxicological data on the repeated dose toxicity is available. Consequently, data on silicon and calcium and their silicates were taken into account.

The main components of CaSi, silicon and calcium, are not suggested to be toxic. Furthermore, e. g. the studies with calcium silicate support the assessment of low toxicity.

 

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Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: lung

Justification for classification or non-classification

Based on the data presented above, it can be concluded that silicocalcium is unlikely to cause any systemic target organ toxicity.

Conclusion: No classification of silicocalcium is suggested.