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Hydrolysis

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Endpoint:
hydrolysis
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Principles of method if other than guideline:
The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).
GLP compliance:
no
Estimation method (if used):
The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).
pH:
4
Temp.:
20 °C
DT50:
0.1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 20-25°C
pH:
7
Temp.:
20 °C
DT50:
0.6 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 20-25°C
pH:
9
Temp.:
20 °C
DT50:
0.1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 20-25°C
Conclusions:
A hydrolysis half-life of approximately 0.1, 0.6 and 0.1 h at pH 4, 7, 9 repsectively, was obtained for the substance using an appropriate calculation method.
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study is well documented and meets generally accepted scientific prinicipels, but was not conducted to an Guideline and GLP.
Principles of method if other than guideline:
Screening method based on H-NMR. OECD mentioned but not specified as guideline followed
pH:
4
DT50:
< 3 min
Type:
(pseudo-)first order (= half-life)
pH:
7
DT50:
29 min
Type:
(pseudo-)first order (= half-life)
pH:
9
DT50:
< 3 min
Type:
(pseudo-)first order (= half-life)

The half lives determined with the method used here, are not very accurate for the very short half lives and generally tend rather to higher values than to be too short. These limitations were considered acceptable, because the main goal of the study was to find out whether the 4 hours half life threshold of the WGK classification can be met or not.

Conclusions:
The hydrolysis half-life of the test substance was measured to be 38 minutes at pH 4, >10 hours at pH 7 and >4 hours at pH 9.
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to an appropriate OECD test guideline, with acceptable restrictions. The restrictions were that analysis of hydrolysis products was not conducted, and other physical chemical properties were not reported
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Buffers:
Buffer solution pH 4, Bipthalate buffer, pH 4 ± 0.02 (25°C)
Buffer solution pH 7, Phosphate buffer, pH 7 ± 0.02 (25°C)
Buffer solution pH 9, Borate/potassium chloride/NaOH buffer, pH 9 ± 0.02 (25°C)
Details on test conditions:
The test item was dissolved in an aqueaous solution at a specific pH-value (pH 4, 7 and () and incubated at a specific temperature. The concentration of the test item was determined as a function of time.
Preliminary study:
According to the guideline, a preliminary hydrolysis test was performed at 50°C ± 0.1 at pH 4, 7 and 9. Aliquots of each test solution were analysed using gas chromatography at the beginning and after 2.4 and 120 hours. Due to the instability of the test item at 50°C. further hydrolysis tests were performed at 20°C, 10°C and 0°C
Transformation products:
not specified
pH:
7
Temp.:
25 °C
DT50:
0.4 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
10 °C
DT50:
1.1 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
0 °C
DT50:
2.3 h
Type:
(pseudo-)first order (= half-life)
Conclusions:
The half-life of the test substance was reported to be 0.4 hrs at pH 7 and 25°C.

Description of key information

Hydrolysis: Half-life approximately 0.4 hours at 25°C and pH 7.

Key value for chemical safety assessment

Half-life for hydrolysis:
0.4 h
at the temperature of:
25 °C

Additional information

A reliable study according to OECD 111 is available for the substance trimethoxyphenylsilane. This substance has a half-life of 0.4 hours at pH 7 and 25°C. Additional information about this endpoint could be gathered through QSAR calculation. A half-life of approximately 0.1, 0.6 and 0.1 hours for the hydrolysis of the substance at pH 4, 7, 9 repsectively was obtained using an appropriate calculation method. The result is considered to be reliable and together with a screening method based on H-NMR which shows a hydrolysis within minutes and supports the fast hydrolysis result from the OECD 111 test.

The half-life of a substance at pH 2 is calculated based on:

t1/2(pH 2) = t1/2(pH 4) / 100

Reaction rate increases with temperature therefore hydrolysis will be faster at physiologically relevant temperatures compared to standard laboratory conditions. Under ideal conditions, hydrolysis rate can be recalculated according to the equation:

DT50(XºC) = DT50(T) x e(0.08.(T-X))

Where T = temperature for which data are available and X = target temperature.

Thus, for trimethoxyphenylsilane the hydrolysis half-life at 37.5 ºC and pH 2 (relevant for conditions in the stomach following oral exposure) and pH 7 (conditions relevant for lungs) is approximately 1 second and 9 minutes repsectively and it is not appropriate to apply any further correction for temperature to the limit value.

The initial hydrolysis products are phenylsilanetriol and methanol.