Silicic acid (H4SiO4), zirconium(4+) salt (1:1), reaction products with sodium hydroxide

Endpoint summary

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

1 372 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

This substance is a UVCB characterised as Silicic acid (H₄SiO₄), zirconium(4+) salt (1:1), reaction products with sodium hydroxide (304-802-4, 94279-56 8). It is the product of a reaction between Zircon (EC no 239-019-6) and sodium hydroxide. 

Inhalation: The substance in water has a pH of >13; it is non-volatile, but is prone to dusting. The high pH makes testing by the inhalation route inappropriate for animal welfare reasons. In addition, REACH Annex VIII requires testing by “the most appropriate route of exposure” where acute testing additional to the oral route is appropriate. As well as animal welfare considerations, testing by the inhalation route would be inappropriate as the severe irritancy affect would mask any systemic toxicity effects. Furthermore, the wealth of data for zirconium salts and silicates indicates a low order of acute toxicity. Toxicity of this substance by the oral route has been assessed. An LD₅₀ of approximately 1300 mg/kg has been established. This further supports the assertion of low systemic toxicity. In addition, an inhalation toxicity study has been conducted for silicic acid, potassium salt (215-199-1), which showed an LC₅₀ of >2.06 mg/L air. Thus, running an acute inhalation study would add nothing to the hazard assessment for this substance, and risk management measures are driven primarily by its corrosive nature due to the high pH. Determination of acute toxicity by the inhalation route is therefore considered inappropriate and unnecessary.

Dermal: The substance in water has a pH of >13. Consequently, it could not be tested as is; it would he theoretically possible to test the material after neutralisation, however, the test substance in this scenario would cease to be the original substance. It would thus be more appropriate to assess the toxicity based on the toxicity of the sodium silicate part of the molecule and assess the systemic toxicity by reading across from other water-soluble zirconium salts. Zirconium acetate has been shown to have a dermal toxicity of >5000 mg/kg; in addition, toxicity of Silicic acid (H₄SiO₄), zirconium(4+) salt (1:1), reaction products with sodium hydroxide by the oral route has been assessed. An LD₅₀ of approximately 1300 mg/kg has been established. This further supports the assertion of low systemic toxicity.  In addition, a dermal toxicity study has been conducted for silicic acid, potassium salt (215-199-1), which showed an LD₅₀ of >5000 mg/kg. Running an acute dermal study would add nothing to the hazard assessment for this substance, and risk management measures are driven primarily by its corrosive nature due to the high pH. Determination of acute toxicity by the dermal route is therefore considered unnecessary.