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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
The study was conducted between 22 November 2016 and 1 February 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Identification: GL500
Alternative names: LGflex GL500
GL500
GL520
CAS No.: 1571954-81-8
Action of test item: Plasticizer
Appearance/Physical state: Clear colorless liquid
Batch: GLFG160607
Purity: 99.6%
Purity/weighing factor: No adjustment for purity will be made.
Expiry date: 07 June 2017
Storage conditions: Room temperature in the dark
Radiolabelling:
not specified
Analytical monitoring:
yes
Details on sampling:
The sample solutions were taken from the waterbath at various times and the pH of each solution recorded.
Buffers:
The test system consisted of sterile buffer solutions at pH’s 4, 7 and 9.

Specification of Buffer Solutions

Buffer solution (pH)
Components Concentration (mol dm-3)
4 Citric acid 0.006
Sodium chloride 0.004
Sodium hydroxide 0.007
7 Disodium hydrogen orthophosphate (anhydrous) 0.003
Potassium dihydrogen orthophosphate 0.002
Sodium chloride 0.002
9 Disodium tetraborate 0.001
Sodium chloride 0.002

These solutions were subjected to ultrasonication and degassing with nitrogen to minimize dissolved oxygen content.
Details on test conditions:
Preparation of the Test Solutions
Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 1 mg/L in the three buffer solutions. A 1% co-solvent of acetonitrile was used to aid solubility.
The test solutions were split into individual vessels for each data point.
The solutions were shielded from light whilst maintained at the test temperature.

Preliminary Test/Tier 1
Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5 °C for a period of 120 hours.

Tier 2
Results from the Preliminary test/Tier 1 showed it was necessary to undertake further testing at pH 4 pH 7 and pH 9, with solutions being maintained at 50.0 ± 0.5 °C, 60.0 ± 0.5 °C and 70.0 ± 0.5 °C for a periods outlined in the following table.

Test pH Peak Test Temperature Test Duration
4 1 50.0 ± 0.5 °C 96 hours
2 192 hours
3 192 hours
1 60.0 ± 0.5 °C 52 hours
2 120 hours
3 120 hours
1 70.0 ± 0.5 °C 30 hours
2 72 hours
3 72 hours
7 1 50.0 ± 0.5 °C 96 hours
2 600 hours
1 60.0 ± 0.5 °C 50 hours
2 288 hours
1 70.0 ± 0.5 °C 30 hours
2 240 hours
9 1 50.0 ± 0.5 °C 21 hours
2 192 hours
1 60.0 ± 0.5 °C 6 hours
2 120 hours
1 70.0 ± 0.5 °C 3 hours
2 72 hours

Duration:
96 h
pH:
4
Temp.:
50 °C
Duration:
192 h
pH:
4
Temp.:
50 °C
Duration:
52 h
pH:
4
Temp.:
60 °C
Duration:
120 h
pH:
4
Temp.:
60 °C
Duration:
30 h
pH:
4
Temp.:
70 °C
Duration:
96 h
pH:
7
Temp.:
50 °C
Duration:
600 h
pH:
7
Temp.:
50 °C
Duration:
50 h
pH:
7
Temp.:
60 °C
Duration:
288 h
pH:
7
Temp.:
60 °C
Duration:
30 h
pH:
7
Temp.:
70 °C
Duration:
240 h
pH:
7
Temp.:
70 °C
Duration:
21 h
pH:
9
Temp.:
50 °C
Duration:
192 h
pH:
9
Temp.:
50 °C
Duration:
6 h
pH:
9
Temp.:
60 °C
Duration:
120 h
pH:
9
Temp.:
60 °C
Duration:
3 h
pH:
9
Temp.:
70 °C
Duration:
72 h
pH:
9
Temp.:
70 °C
Number of replicates:
3 at pH4, 2 at ph 7 and pH9
Positive controls:
no
Negative controls:
no
Preliminary study:
pH4 @ 50 ºC Result: The extent of hydrolysis after 120 hours indicated that a further test (Tier 2) was required to estimate the rate constant and half-life at 25 °C.
pH7 @ 50 ºC Result: The extent of hydrolysis after 120 hours indicated that a further test (Tier 2) was required to estimate the rate constant and half-life at 25 °C.
pH9 @ 50 ºC Peak 1 Result: The extent of hydrolysis after 120 hours indicated that a further test (Tier 2) was required to estimate the rate constant and half-life at 25 °C.
pH9 @ 50 ºC Peak 2 Result: The extent of hydrolysis after 120 hours indicated that a further test (Tier 2) was required to estimate the rate constant and half-life at 25 °C.
pH9 @ 50 ºC Peak 3 Result: Less than 10% hydrolysis after 5 days at 50 °C, equivalent to a half-life greater than 1 year at 25 °C.
Test performance:
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0.05 to 1.50 mg/L under pH 4, 7 and 9 conditions. The results were satisfactory with correlation coefficients (r) of ≥ 0.999 being obtained. For all pH’s
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
Details on hydrolysis and appearance of transformation product(s):
Usually, hydrolysis products should be identified using LC-MS or GC-MS. However, this procedure implies sufficient separation of the individual components that are present in the incubated test item solution (i.e. parent compound and hydrolysis products). LC-MS was carried out on the parent peaks to confirm their identity based on the sponsor’s information. The chromatography of the incubated test solution resulted in several peaks that could not be separated sufficiently from each other, and eluted at the dead time.

Referencing of the structural information provided by the sponsor, the hydrolysis products were 2-ethylhexanol, 1-butanol or 1,4 benzene dicarboxylic acid.
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0.002 h-1
DT50:
11.7 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
32.8 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
69.5 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
5.8 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
131 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.023 h-1
DT50:
1.23 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
98.1 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Details on results:
The kinetics of the study has been determined to be consistent with that of a pseudo-first order based on the nearly linear graphs of log10 concentration versus time producing linear Arrhenius plots.
No significant peaks were observed at the approximate retention time of the test item in the matrix blank solutions.
Validity criteria fulfilled:
yes
Conclusions:
The estimated rate constant and half-life at 25 °C of the test item are shown in the following table:

pH Peak Estimated rate constant (hr-1) at 25 °C Estimated half-life at 25 °C
4 1 2.48 x 10-3 11.7 days
2 8.79 x 10-4 32.8 days
3 4.16 x 10-4 69.5 days
7 1 4.98 x 10-3 5.80 days
2 2.20 x 10-4 131 days
3 - > 1 year
9 1 2.34 x 10-2 1.23 days
2 2.94 x 10-4 98.1 days
3 - > 1 year
Executive summary:

The hydrolysis as a function of pH of GL500 has been determined, using a procedure designed to be compatible with Method C.7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004. The results are as follows:

 pH  Peak  Estimated rate constant (h-1) at 25 °C  Estimated half-life at 25 °C
4

1

 2.48 x 10-3  11.7 days
 2  8.79 x 10-4  32.8 days
 3  4.16 x 10-4  69.5 days
7  1  4.98 x 10-3  5.80 days
 2  2.20 x 10-4  131 days
 3  -  > 1 year
9         1  2.34 x 10-2  1.23 days
 2  2.94 x 10-4  98.1 days
 3  -  > 1 year

Description of key information

The estimated rate constant and half-life at 25 °C of the test item are shown in the following table:

 pH  Peak  Estimated rate constant (h-1) at 25 °C  Estimated half-life at 25 °C
4

1

 2.48 x 10-3  11.7 days
 2  8.79 x 10-4  32.8 days
 3  4.16 x 10-4  69.5 days
7  1  4.98 x 10-3  5.80 days
 2  2.20 x 10-4  131 days
 3  -  > 1 year
9         1  2.34 x 10-2  1.23 days
 2  2.94 x 10-4  98.1 days
 3  -  > 1 year

Key value for chemical safety assessment

Additional information

A singular half life cannot be identified for the substance as it is a UVCB. As one of the components was found to have a long half life (greater than a year) and this component is understood to be DOTP which is typically present at greater than 50%. The overall substance must be considered hydrolytically stable.