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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
25 November 2019 - 06 December 2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling method:
Tier I: Before the solutions were placed in the incubator, the samples of them were taken out, signed as “Day 0” samples. After 5 days, the next samples were taken from the examined testing solutions (pH 4, 7 and 9, 50 ºC). Duplicate samples were taken at each pH.
- Sampling intervals/times for pH measurements:
Tier I: Duplicate samples at each pH were taken at day 0 and day 5.


Buffers:
- pH: Buffers solutions of pH 4.0, pH 7.0 and pH 9.0.



Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks: glass flasks fitted with glass stoppers
- Other equipment used: incubator and magnetic stirrer
- Lighting: darkness.

TEST MEDIUM
- Preparation of test medium:
Tier I: About 0.5 g of test item was weighed and dissolved in 50 mL of the 3 buffer solutions. After 2 days of saturation the solutions were centrifuged to separate the excess of test item and 2 times diluted (half-saturated solutions).
Duration:
5 d
pH:
4
Temp.:
50 °C
Initial conc. measured:
1.022 mg/L
Remarks:
Average concentration of 2 replicates.
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
0.778 mg/L
Remarks:
Average concentration of 2 replicates.
Duration:
5 d
pH:
9
Temp.:
50 °C
Initial conc. measured:
1.093 mg/L
Remarks:
Average concentration of 2 replicates.
Number of replicates:
Preliminary test Tier 1: two replicates
Positive controls:
no
Negative controls:
no
Preliminary study:
After 5 days of the study the concentration of test item drastically dropped at the three pHvalues (4.0, 7.0 and 9.0) but it was not caused by the hydrolytic decomposition, but by the evaporation process.
Test performance:
Further testing was not necessary as no hydrolysis was experimentally found during the preliminary test.
Transformation products:
no
% Recovery:
4
pH:
4
Temp.:
50 °C
Duration:
5 d
Remarks on result:
other: This is not a result of hydrolysis but of the evaporation of the test substance.
% Recovery:
7
pH:
7
Temp.:
50 °C
Duration:
5 d
Remarks on result:
other: This is not a result of hydrolysis but of the evaporation of the test substance.
% Recovery:
19
pH:
9
Temp.:
50 °C
Duration:
5 d
Remarks on result:
other: This is not a result of hydrolysis but of the evaporation of the test substance.
Key result
Remarks on result:
not determinable
Remarks:
(the concentration of test item drastically dropped due to evaporation)
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): evaporation of the test substance took place at the three values of pH during the preliminary test thus no further testing was performed.


Table 1: Study solutions in buffers – day 0

Sample

No

Weight

of the sample

[mg]

Dilution

[ml]

Cp

[mg/ml]

Peak area

Average peak area

Ap

X

[mg/l]

pH4-1

5181.20

5

1036.240

30.07

33.28

31.675

1.0573

pH4-2

5106.80

5

1021.360

29.24

29.04

29.12

0.9862

pH7-1

5084.10

5

1016.820

24.76

24.5

24.63

0.8378

pH7-2

5084.90

5

1016.980

22.08

20.08

21.08

0.7170

pH9-1

4905.20

5

981.040

31.07

33.43

32.25

1.1370

pH9-2

5052.90

5

1010.580

30.13

31.15

30.64

1.0487

Table 2: Study solutions in buffers – after 5 days

Sample

No

Weight

of the sample

[mg]

Dilution

[ml]

Cp

[mg/ml]

Peak area

Average peak area

Ap

X

[mg/l]

pH4-1

5181.50

5

1036.300

1

0.85

0.93

0.0354

pH4-2

5152.10

5

1030.420

0.95

1.29

0.90

0.0431

pH7-1

5145.70

5

1029.140

1.86

1.13

1.50

0.0576

pH7-2

5093.60

5

1018.720

1.13

1.64

1.39

0.0539

pH9-1

5049.70

5

1009.940

4.8

5.22

5.01

0.1965

pH9-2

5053.50

5

1010.700

5.4

5.24

5.32

0.2086

Table 3: Measurements in buffer solution at pH 4.0

Time, days

0

5

concentration, [mg/l]

1 flask

1.057

0.035

2 flask

0.986

0.043

pH

4.02

4.02

average concentration, [mg/l]

1.022

0.039

concentration loss,  [%]

96

Table 4: Measurements in buffer solution at pH 7.0

Time, days

0

5

concentration, [mg/l]

1 flask

0.838

0.058

2 flask

0.717

0.054

pH

6.99

6.99

average concentration,  [mg/l]

0.778

0.056

concentration loss,  [%]

93

Table 5: Measurements in buffer solution at pH 9.0

Time, days

0

5

concentration, [mg/l]

1 flask

1.137

0.197

2 flask

1.049

0.209

pH

8.98

8.98

average concentration, [mg/l]

1.093

0.203

concentration loss,  [%]

81

After 5 days of the study the concentration of test item drastically dropped but it was not caused by the hydrolytic decomposition, but by the evaporation process. To prove that fact additional test was performed. A water solution of the same concentration as in Tier 1 was prepared and saturated for 30 minutes, then it was centrifuged to separate the excess of test item and 2 times diluted (to obtain half saturated solution in water). The solution directly after preparation was passed to analysis, it was then incubated in 20ºC and analyzed again after 1 and 2 days (see figures 1 and 2 below). The aim of this additional test was to verify and demonstrate how fast was the concentration drop of the test item and if there was any additional and increasing peaks which could indicate that the hydrolysis process took place.

A significant decrease in the test item concentration was observed for the 3 consecutive days (figure 1 below) and the remaining peaks, which appeared under analysis conditions only after previous extraction of the test item from the aqueous solution and which are probably some impurities of the test item (figure 2 below), remained almost constant during all three days of the test. This was suggested as a prove that the the test item does not decompose but evaporates.

Validity criteria fulfilled:
yes
Remarks:
(Selectivity: no other peaks interfering with the substance peak; linearity: R2 > 0.99; precision RSD 2.68% (approval criteria < 6.88%) and RSD for repeatibility was 1.30% (approval criteria < 1.34%))
Conclusions:
The test substance does not undergo hydrolytic decomposition but instead it evaporates sharply from the test medium under the experimental conditions.


Executive summary:

An Hydrolysis study was conducted on the test substance, according to OECD TG 111 (Hydrolysis as a function of pH), GLP Study. A validated GC method was used for determining the content of the test substance in the samples. Duplicate half-saturated test item solutions were prepared in buffer solutions for the pH values of 4.0, 7.0 and 9.0. The preliminary test (Tier 1) was performed in a dark incubator at the temperature of 50ºC. After 5 days of the study the concentration of test item drastically dropped but it was not caused by the hydrolytic decomposition, but by an evaporation process. To prove that fact an additional test was performed. A water solution of the same concentration as in Tier 1 (half-saturated) was incubated in 20ºC and analyzed for 3 consecutive days. During this additional test a significant decrease in the test item concentration was observed and the remaining peaks, which are probably some impurities of the test item, remained almost constant during all three days of the test. However, no additional or increasing peaks which could indicate that the hydrolysis process took place were found by the GC analysis. This was suggested as an evidence that the the test item does not decompose but evaporates. In conclusion, the test item was found to be a highly volatile substance that cannot be kept in solution under the experimental conditions and, according to the test method, it should not be subjected to the hydrolysis study.

Description of key information

Key study. Method according to OECD 111, GLP Study. The test substance does not undergo hydrolytic decomposition but instead it evaporates sharply from the test medium under the experimental conditions.

Key value for chemical safety assessment

Additional information

The results found in the present hydrolysis study on the test item alpha terpinene are consistent with the conclusions included in the CLH report on alpha terpinene from March 2018 (available in ECHA website): Alpha-Terpinene does not contain any functional groups that are susceptible to hydrolysis under environmental conditions. Therefore, hydrolysis of the substance is not expected in aquatic environments.The substance is considered to be highly volatile and will dissipate from water rapidly. Based on the Henry’s law constant, alpha-terpinene is expected to partition from water and soil to air. Rapid escape (fugacity via volatility) appears to be the predominant cause of dissipationfor alpha-terpinene in natural waters. No degradation products in water were detected. Soil degradation studies showt hat the fate of alpha-terpinene in soil is of limited relevance as it volatilises and evaporates rapidly into the air compartment.