Silicic acid, calcium salt

Endpoint summary

Description of key information

The acute oral administration of >=5000 mg calcium silicate/kg bw  failed to produce signs of toxicity or deaths in treated animals.   
Based on structure analogy to SAS, the acute inhalation of Ca silica dust may cause discomfort and dyspnea as well as transient signs of local irritation to nasal, bronchiolar and ocular mucous membranes. 

Additional information

Summary of acute target-organ effects

• Oral uptake

Based on experimental results from CS and the structure-analogous SAS, there is ample evidence that high oral doses of CS do not exert any significant toxicity in experimental animals.

• Inhalation

No corresponding studies with CS have been located. On the other hand, experimental data is available about structure-analogous silicas (SAS) which resulted in no mortality under test conditions.

Summary of results obtained with SAS :

All acute inhalation studies performed with dry dust of SAS were hampered by the technical problem to achieve the

recommended highest test concentration of 5 mg/L, apparently attributable to the high adhesive forces which caused rapid precipitation onto equipment walls. Therefore, the maximum attainable chamber concentrations were distinctly lower than envisaged.  

In one study, all ten rats (5 m, 5 f) survived when exposed to an average concentration of 2.08 mg/L of pyrogenic SAS, Cab-O-Sil M5, (MMAD = 0.76 µm) for 4 hours. Clinical symptoms were nasal discharge during exposure, in a few animals crusty eyes and nose as well as alopecia at days post-exposure. No macroscopic organ lesions were noted but in one animal discoloration of the lungs was observed [Cabot 1981].

In a further study, an average dust concentration of 0.691 mg/L (range 0.650 – 0.725 mg/L) for the precipitated SAS, Sipernat 22,

was obtained, with a respirable mass fraction of some 45 to 47 % accounting for particles with a mass median aerodynamic diameter (MMAD) of less than 5 µm [Degussa 1983]. No clinically and pathologically meaningful effects were observed after 4-h exposure

of rats (5 m, 5 f, each). The animals showed signs of some discomfort and stress, and body weight of females was retarded for two days post-exposure.

Justification for classification or non-classification

Synthetic amorphous silicates and silicas (SAS) are practically non-toxic by all routes of exposure. Aerosol levels that were technically achievable for SAS under experimental conditions are acutely non-toxic and clearly sub-lethal (=< 2 mg/L). Under comparable testing conditions we expect that synthetic amorphous calcium silicate shows the same behaviour.

No classification for acute human health hazards shall be required.