Di-tert-butyl trisulphide

Hydrolysis

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

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Di-tert-butyl trisulphide

EC Number:

224-226-6

EC Name:

Di-tert-butyl trisulphide

Cas Number:

4253-90-1

Molecular formula:

C8H18S3

IUPAC Name:

di-tert-butyltrisulfane

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.