Reaction mass of calcium disilicide and calcium silicide

Endpoint summary

Description of key information

There is no data on acute oral, dermal or inhalation toxicity of  silicocalcium. Therefore, weight of evidence approach is utilised in which the information on the toxicity of constituents and related compounds are used.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

5 000 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Dose descriptor:

LC50

Value:

2 000 mg/m³ air

Acute toxicity: via dermal route

Endpoint conclusion

Dose descriptor:

LD50

Value:

5 000 mg/kg bw

Additional information

There were no data on acute non-human toxicity via oral route with silicocalcium. Therefore, weight of evidence approach is utilised. This means the use of information on the toxicity of composites (e.g. silicon and calcium) and related compounds - such as calcium silicate, which has similar order of water solubility releasing both silicon and calcium (OECD 2004).

Silicocalcium contains 55-63 wt-% of silicon and 28-32 wt-% of calcium. Other relevant constituents include iron and aluminium, which comprise up to 10 and up to 2.5 wt-% of the silicocalcium, respectively. The surface of silicocalcium is composed mainly of silicon and calcium rich oxides. Silicon is released from CaSi at similar or somewhat lower levels than from amorphous silicon dioxide (pyrogenic silica). The release of iron from silicocalcium is very restricted and resembles the release of iron from pyrogenic silica. Thus, amorphous silica is used for read-across in the assessment of the toxicity of CaSi. However, since significant levels of calcium are also released from CaSi matrix the impact of this element on the acute toxicity of CaSi should be also assessed.

Also small amounts of aluminium are released from silicocalcium matrix in synthetic biological fluids in vitro. In the assessment of the acute toxicity of silicocalcium, the possible impact of aluminium on the toxicity of silicocalcium should be taken into account.

Acute oral toxicity of amorphous silicon dioxide is >2000 mg/kg in rats. Also calcium silicate, which has the same order of water solubility than with CaSi and which release both silicon and calcium has shown low acute oral toxicity (LD₅₀,rats >......)

Calcium (present in ferrosilicocalcium 28-32% w/w) is not acutely toxic as poorly soluble compound (oral LD₅₀>2,000 mg/kg) and even the water soluble calcium chloride has LD₅₀of 1,000 mg/kg.

Aluminium is a minor composing element of silicocalcium, The acute toxicity of metallic aluminium and aluminium compounds has been studied to be low, the reported oral LD₅₀values being in the range of several hundred to 1,000 mg aluminium/kg body weight per day (EHC 1997). Furthermore, the LC₅₀values for inhalation have not been identified for aluminium and its compounds (EHC 1997). Thus, silicocalcium unlikely has acute oral toxic properties.

Inhalation and dermal acute toxicity of silicon is low (do not exceed the classification limits).

Following inhalation exposure of rats to the highest technically feasible concentrations of 140 to ca. 2,000 mg/m³synthetic amorphous silica, no lethal effects were observed. The acute inhalation of synthetic amorphous silica dust may cause discomfort and stress as well as sign of local irritation to nasal, bronchiolar and ocular mucous membranes. Read across from the synthetic amorphous silica dusts suggests that calcium silicon is acutely non-toxic via inhalation.

Justification for classification or non-classification

Conclusion: Silicocalcium is not acutely toxic via oral, inhalation or dermal route.