Silicic acid, calcium salt

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23/08/2010 - 28/09/2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Extrapolation from water solubility study according to international guideline under GLP.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: water solubility

Principles of method if other than guideline:

Extrapolation of results obtained from water solubility study according to OECD guideline 105 using the shake-flask method (see chapter 4.8).

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Not relevant

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples were taken on days 1, 2, 3, 6, 7, 8, 9 and 13.

Buffers:

Not relevant

Estimation method (if used):

Not relevant

Details on test conditions:

Preliminary test

In 10 mL centrifuge vials, 0.1171 g of the test item was weighed. Different volumes of water were added, ranging from 0.1 mL to 10 mL. No complete dissolution was observed. 10.7 mg of the test item were mixed with 1000 mL water and the mixture was shaken for 72 hours. After this time, undissolved particles could be detected in the flask; therefore solubility was estimated as < 10 mg/L. The resulting solution was filtrated and measured. Ca concentration lay by 2.36 mg/L Ca. Therefore, the column elution method was chosen for the determination of the solubility of crystalline calcium silicate hydrates (xonotlite – tobermorite). The measurements of the overnight collected solution by AAS gave a Ca concentration of 4.8 mg/L. Therefore, the column elution method was aborted, and the flask method was used for the determination of the solubility of the test item in water. Si pre-test of this solution was also performed, but not described in the final report.

As no Ca content in the test item was known at that moment, secondary pre-test after the determination of the Ca content was performed. 100 mg of the test item mixed with 30 ml water and the mixture was shaken for 22 hours. After this time the solution was filtrated, diluted (1 : 10 and 1: 100) and measured via AAS for Ca. Ca concentration of the first dilution (1 : 10) lay at 1.7 mg/L Ca, corresponding to the approx. 100 mg/L test item (from the Ca content of 17.19%). Therefore, the flask method was chosen for the determination of the solubility of crystalline calcium silicate hydrates (xonotlite – tobermorite).

Main test
The value which was detected in the preliminary study was used to calculate the amount of test item which is necessary to saturate 1000 ml as approx. 100 mg. Six vessels were used. 25 – 65 mg crystalline calcium silicate hydrates (xonotlite – tobermorite) were weighed into the six vessels, 50 mL water (p.A.) was added to each vessel. The sealed flasks were put on the orbital shaker.
Shaking was performed for 24 hours, then, vessel 1 was taken from the shaker and left to stand at 20 ± 0.5°C for equilibration, followed by the first sampling. The flask was put back on the shaker, and the sample was prepared for analysis and measured Ca, giving the value for day 1. The following samples were taken in the same manner on the days 2, 3, 6, 7, 8, 9 and 13.

Duration:

14 d

pH:

10

Temp.:

20 °C

Initial conc. measured:

100 mg/L

Remarks:

details described in test conditions

Number of replicates:

Not relevant

Positive controls:

no

Negative controls:

no

Statistical methods:

No data

Preliminary study:

No data

Test performance:

No data

Transformation products:

not specified

Details on hydrolysis and appearance of transformation product(s):

The substance decomposes for a small part in Ca2+ and SiO3(2-) which in water transforms into the solid SiO2

Key result

pH:

10

Temp.:

20 °C

DT50:

< 6 d

Type:

not specified

Other kinetic parameters:

No data

Details on results:

It was shown that after 14 days, 37 mg of the substance was transformed in water. This plateau was reached after 6 days. This resulted in a hydrolyis rate half-life of less than 6 days.

No data

Validity criteria fulfilled:

not applicable

Conclusions:

The hydrolysis rate of crystalline calcium silicate hydrate (xonotlite - tobermorite) is < 6 days.

Executive summary:

Information on the hydrolysis rate of crystalline calciium silicate hydrate (xonotlite - tobermorite) was derived from a water solubility study (see chapter 4.8). It was shown that after 14 days, 37 mg of the substance was transformed in water. This plateau was reached after 6 days. This resulted in a hydrolyis rate half-life of less than 6 days.

Description of key information

Hydrolysis DT50: <6 days

Key value for chemical safety assessment

Half-life for hydrolysis:

6 d

at the temperature of:

20 °C

Additional information

Information on the hydrolysis rate of silicic acid, calcium salt was derived from a water solubility study (see chapter 4.8). It was shown that after 14 days, 37 mg of the substance was transformed in water. This plateau was reached after 6 days. This resulted in a hydrolyis rate half-life of less than 6 days.