Registration Dossier

Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2011
Report Date:
2011

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Radiolabelling:
no

Study design

Analytical monitoring:
yes
Details on sampling:
weighting, accuracy 0.1 mg
stock solution in acetonitrile 1 mg/ml
sterility control
Buffers:
- pH: 4
- Type and final molarity of buffer: 4.0-4.1
- Composition of buffer:C8H5KO4/NaOH

- pH: 7
- Type and final molarity of buffer: 7.0-7.2
- Composition of buffer:KH2PO4/NaOH

- pH: 9
- Type and final molarity of buffer: 8.9-9.2
- Composition of buffer:H2BO3-KCl/NaOH
Details on test conditions:
Solutions in buffers were prepared at a concentration of 3.5 mg/L estimated to be half the water solubility limit.
2 preliminary tests were done at 50°C for each of the 3 pH (4, 7 and 9).
Samplings were done at time = 0, 2.4, 24 and 120 hours for 1st preliminary test and at 0 and 120 hours for the 2nd.
In view of the preliminary ests results, a definitive test was done at pH4, at 20, 50 and 65°C
Sterility controls were done (result: no CFU were observed).
Number of replicates:
one solution, 2 samples at each time.
Positive controls:
no
Negative controls:
no

Results and discussion

Preliminary study:
In a preliminary test the test item was dissolved in aqueous solutions buffered at pH 4, 7 and 9 and incubated at 50 ± 0.6 °C for maximum of 5 days. At pH values 4 and 7 after 5 days incubation period the test item concentration was found to be below 90 % of the initial concentration.
To verify the results the pre-test was repeated for all three pH values. In case of the pH 7 and 9 the test item reduction was less than 10%. In case of pH 4 a reduction of 16% of the initial value was observed. Although the reduction was only small and a hydrolysis of the test item is very unlikely. A main test was performed at pH 4 to determine the half-life time of Polysulfides, di-tert-Bu at pH 4.
Test performance:
The test item was dissolved and incubated at approx. 20 °C, 50 °C and 65 °C. The concentration of the test item was determined as a function of time over a period of 32 days. The concentrations were plotted against the time. No clear decrease pattern in the test item concentration can be observed for the solution at pH 4. In case of the experiment performed at 20°C a reduction in concentration of 15% was measured from 5 day incubation to 11 day incubation. However during the further 21 days of the experiment the concentration did not changed by more than 10%. For the experiments performed at 50°C and 65°C a decrease in the test item concentration was observed at begin of the incubation period. However in the course of the experiment the concentration fluctuated and no clear decrease was observed.
Transformation products:
no
Dissipation DT50 of parent compound
Remarks on result:
other: See remarks
Remarks:
Hydrolysis is not the mechanism by which the registered substance degrades.
Details on results:
According to the pre-test performed at 50°C the test item is considered hydrolytically stable at pH 7 and 9. For pH 4 the outcome of the experiments gives no clear indication on the hydrolytic properties of the test item. No consistent decrease was observed.Furthermore a hydrolysis of the sulfide bond is not very likely. Thus the observed decrease in concentration is supposed not to be a consequence of a hydrolysis reaction.

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes. Sterility was checked with incubation of samples on agar-agar.
- Anomalies or problems encountered (if yes): no significant

Any other information on results incl. tables

Table 1: Results of the first preliminary test at 50°C

pH

Incubation time

Measured concentration (mg/L)

Calculated reduction (%)

Measured pH

4

0

2.884

0

4.1

0

2.824

4.1

2.4

3.181

-12

4.1

2.4

3.058

-7

4.1

24

2.837

1

4.1

24

2.851

0

4.1

120

2.629

8

4.1

120

2.349

18

4.1

 

0

2.919

0

7.0

0

2.704

7.0

2.4

2.798

1

7.0

24

2.621

7

7.0

24

2.439

13

7.0

120

2.340

17

7.0

120

2.349

17

7.0

9

0

3.085

0

9.0

0

3.099

9.0

2.4

3.227

-4

8.9

2.4

3.063

1

8.9

24

3.017

2

8.9

24

2.764

11

9.0

120

3.017

2

9.0

120

2.925

5

9.0

Table 2: Results of the second preliminary test at 50°C

pH

Incubation time

Measured concentration (mg/L)

Calculated reduction (%)

Measured pH

4

0

3.077

0

4.0

0

3.078

4.0

120

2.645

14

4.1

120

2.515

18

4.1

7

0

3.216

0

7.2

0

3.152

7.2

120

3.170

1

7.1

120

2.773

13

7.1

9

0

3.292

0

9.2

0

3.195

9.2

120

2.992

8

9.0

120

2.971

8

9.0

Table 3: Results of the definitive test at pH 4 and 20°C

pH

Incubation time

Measured concentration (mg/L)

Calculated reduction (%)

4

0

3.077

0

0

3.078

120

2.645

9

120

2.515

9

264

3.216

28

264

3.152

20

432

3.170

27

432

2.773

24

600

3.292

34

600

3.195

37

768

2.992

27

768

2.971

35

Table 4: Results of the main test at pH 4 and 50°C

pH

Incubation time

Measured concentration (mg/L)

Calculated reduction (%)

4

0

3.160

0

0

3.143

120

2.605

17

120

2.465

22

264

2.154

32

264

2.061

35

432

2.192

30

432

2.124

33

600

1.984

37

600

1.873

41

768

2.214

30

768

2.384

24

Table 5: Results of the definitive test at pH 4 and 65°C

pH

Incubation time

Measured concentration (mg/L)

Calculated reduction (%)

4

0

3.323

0

0

3.158

120

2.496

23

120

2.523

22

264

2.073

36

264

1.805

44

312

2.242

31

312

2.264

30

432

2.079

36

432

1.689

48

600

1.578

51

600

1.846

43

768

2.329

28

768

2.735

16

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
The test item is considered abiotically stable at pH 7 and 9 under aqueous conditions in the dark. For pH 4, degradation reached a plateau after approximately one third of degradation. The results were inconsistent with an hydrolytic mechanism. Another degradation mechanism is probably at play where an equilibrium is reached with a degradation product (may be in a 2:1 ratio). The degradation rate is low and it is not expected that this would affect the persistency of the substance in the aquatic environment.
Executive summary:

Aqueous abiotic degradation of polysulfides di-tert-butyl was investigated in a GLP study following OECD TG 111. The purpose of the study was to determine the rate of hydrolysis of the substance (if any) at different environmentally relevant pH. In the preliminary test (tier 1), the test item was dissolved in buffered aqueous solutions (pH 4 - 7 - 9) and incubated at 50°C for 5 days. After 5 days incubation at pH 4 and 7, the test item concentration was found at concentrations slightly below 90% of the initial concentration. Since hydrolysis was not expected with regards to the structure of the substance, the preliminary test was conducted twice at all pH. After 5 days incubation at 50°C, the test item concentration was found above 90% of the initial concentration at pH 7 and 9. The test item concentration still continue to be slightly lower than 90% of the initial concentration at pH 4 (84%). Therefore, the main test was conducted for pH 4 only.

The test item was dissolved in aqueous solution buffered at pH 4. The solutions were incubated at 20°C, 50°C and 65°C. The concentration of the test item was determined after different incubation times. A HPLC method was used for determination of the concentration of the test item. No clear decreasing trend was observed. A decrease of 15% reached a plateau after 11 days incubation at 20°C. At 50°C and 65°C, concentrations fluctuated and no clear decrease was observed.

According to the pre-test performed at 50°C, the test item is considered abiotically stable at pH 7 and 9 under aqueous conditions in the dark. For pH 4, degradation reached a plateau after approximately one third of degradation. The results were inconsistent with an hydrolytic mechanism. Another degradation mechanism is probably at play where an equilibrium is reached with a degradation product (may be in a 2:1 ratio). The degradation rate is low and it is not expected that this would affect the persistency of the substance in the aquatic environment.