Silicic acid, aluminum sodium salt

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Jun. 4 - Nov. 18, 2019; experimental phase: Jun. 4 - 27, 2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Name: Silicic acid, magnesium aluminium sodium salt
Batch no.: 201810LC007
Appearance: white fluffy powder
Composition: Sodium; Magnesium; Aluminium; Silica
Purity: >95%
Homogeneity: homogeneous
Specific surface area: 57.9 m²/g

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

The same sample preparation was performed on day 0 and 5.
Before measurement of the solutions via ICP-OES for Si (blanks and test item solutions) tenfold dilution was performed: 0.5 mL of the solution were added to 4.5 mL water p.a. and measured via ICP-OES.

Buffers:

Buffer-Solution, pH 4
Parameter Amount
CH3COOH, 2 M 80 mL
CH3COONa, 1 M 40 mL
Water p.a. ad. 1000 mL
Three replicates were prepared and combined; pH was measured as 4.02 (batch A20190603).
For batch A20190613 (used in the Tier 1), two replicates were prepared and combined; pH was measured as 4.0.

Buffer-Solution, pH 7
Batch A20190604:
Parameter Amount
KH2PO4 8.7085 g
Water p.a. 500 mL
NaOH, 2 M 14.9 mL
Water p.a. ad. 1000 mL
Three replicates were prepared and combined; pH was adjusted with 2 M NaOH to 7.04.
Batch A20190613 (used in the Tier 1):
Parameter Amount
KH2PO4 8.7089 g / 8.7079 g (for replicate 1 and 2)
Water p.a. 500 mL
NaOH, 2 M 14.9 mL
Water p.a. ad. 1000 mL
Two replicates were prepared and combined; pH was adjusted with 2 M NaOH to 7.00.

Buffer-Solution, pH 9
Batch A20190604:
Parameter Amount
H3BO3 3.093 g
KCl 3.729 g
Water p.a. 500 mL
NaOH, 2 M 10.75 mL
Water p.a. ad. 1000 mL
Three replicates were prepared and combined; pH was adjusted with 2 M NaOH to 9.00.
Batch A20190613 (used in the Tier 1):
Parameter Amount
H3BO3 3.0927 g / 3.0926 g (for replicate 1 and 2)
KCl 3.7298 g / 3.7294 g (for replicate 1 and 2)
Water p.a. 500 mL
NaOH, 2 M 10.75 mL
Water p.a. ad. 1000 mL
Two replicates were prepared and combined; pH was adjusted with 2 M NaOH to 9.03.

Estimation method (if used):

The analytical determination of the test item was performed via measurement of Silicon (Si), Magnesium (Mg) and Aluminium (Al) via ICP-OES.

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

41.67 mg/L

Remarks:

silicon

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

46.35 mg/L

Remarks:

silicon

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

36.6 mg/L

Remarks:

silicon

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

384.7 mg/L

Remarks:

magnesium

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

20.21 mg/L

Remarks:

magnesium

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

3.948 mg/L

Remarks:

magnesium

Number of replicates:

2 (+ blank controls)

Positive controls:

no

Negative controls:

yes

Preliminary study:

The test item was considered to be stable and no further examination was made.

s. below on detailed results

Transformation products:

no

% Recovery:

> 100

St. dev.:

0

pH:

4

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: Si content

% Recovery:

92.2

St. dev.:

1.5

pH:

7

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: Si content

% Recovery:

93.4

St. dev.:

0.5

pH:

9

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: Si content

% Recovery:

100

St. dev.:

0.6

pH:

4

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: Mg content

% Recovery:

98.2

St. dev.:

2.7

pH:

7

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: Mg content

% Recovery:

96

St. dev.:

0.3

pH:

9

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: Mg content

Key result

Temp.:

25 °C

DT50:

> 365 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

hydrolytically stable based on preliminary test

The half saturated solutions with the nominal load 50 g/L in pH 4, 7 and 9 buffer solutions were measured for Si, Al and Mg on day 0 and after the storage of the test solutions at 49.7 – 50.2 °C for 5 days. The concentration of Al in pH 4, 7 and 9 buffer solutions was below the LOQ of the respective method at each sampling point (< 0.05 mg/L in pH 4 and 9 solutions and < 0.02 mg/L in pH 7 solutions). Therefore, the calculation of the stability of the test item in buffer solutions based on Al was not possible. All measurements lay below the LOD of the Tyndall device (< 3 mg/L particle concentration).

Recovery rate based on solid content reformation of inorganic salts (ICP-OES measured Si content): pH = 4: 102.9%; pH = 7: 92.2%, pH = 9: 93.4%. As the amount of Si and Mg after five days was more than 90% of the amount at the start of the test, the test item was considered to be stable (following OECD, t(0.5) at 25 °C is then greater than 1 year), and no further examination was made.

Validity criteria fulfilled:

yes

Conclusions:

The concentration of Al in pH 4, 7 and 9 buffer solutions lay below the LOQ of the respective method at each sampling point (< 0.05 mg/L in pH 4 and 9 solutions and < 0.02 mg/L in pH 7 solutions). Therefore, the calculation of the stability of Al in buffer solutions was not possible.
As the amount of Si and Mg after five days was more than 90 % of the amount at the start of the test, the test item was considered to be stable (following OECD, t(0.5) at 25 °C is then greater than 1 year), and no further examination was made.
Recovery rate based on solid content, reformation of inorganic salts (ICP-OES measured Si content):
pH=4: ca. 100 %; pH=7: 92.2 %; pH=9: 93.4 %

Executive summary:

This study was performed in order to determine the hydrolysis behaviour of Silicic acid, magnesium aluminium sodium salt and stability of dissolved test item in dependence of the pH.

Aqueous buffer solutions of different pH values (pH 4, 7 and 9) were treated with the test item and the filtrated test item solutions were incubated in the dark under controlled laboratory conditions (at constant temperature). After appropriate time intervals, buffer solutions were analysed for Silicon (Si), Magnesium (Mg) and Aluminium (Al) via ICP-OES. The concentration of Sodium (Na) was not determined as Sodium is present in all buffer solutions. Potentially available undissolved particles in the filtrated test item solution were measured using Tyndall device.

Description of key information

The read-across substance Silicic acid, aluminum magnesium sodium salt (CAS 12040-43-6, SMAS) was assessed as follows:

The concentration of Al in pH 4, 7 and 9 buffer solutions lay below the LOQ of the respective method at each sampling point (< 0.05 mg/L in pH 4 and 9 solutions and < 0.02 mg/L in pH 7 solutions). Therefore, the calculation of the stability of Al in buffer solutions was not possible.
As the amount of Si and Mg after five days was more than 90 % of the amount at the start of the test, the test item was considered to be stable (following OECD 111, t(0.5) at 25 °C is then greater than 1 year), and no further examination was made.
Recovery rate based on solid content, reformation of inorganic salts (ICP-OES measured Si content):
pH=4: ca. 100 %; pH=7: 92.2 %; pH=9: 93.4 %

Key value for chemical safety assessment

Half-life for hydrolysis:

366 d

at the temperature of:

25 °C

Additional information

Since no studies investigating the hydrolysis of Silicic acid, aluminum sodium salt (CAS 1344-00-9, NAS) are available, a read-across to a structurally related silicic acid species was conducted. This read-across is justified within the analogue justification in IUCLID Section 13.