Tetrakis(diethyldithiocarbamato-S,S')tellurium

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23 Apr 2018 to 11 Jun 2018

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)

Version / remarks:

April 2004

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

- Name of test material (as cited in study report): Tellurium diethyldithiocarbamate (TDEC)
- Purity: 100%
- Tellurium content: 17.6%
- Batch No.: 60701019
- Date of manufacture: 09-02-2017
- Date of analysis: 16-06-2017

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

TIER 1:
- pH 4 at 50 °C: Samples were taken at 0, 30, 60, 120, 240 and 360 min.
- pH 7 at 50 °C: Samples were taken at 0, 30, 60, 120, 240 and 360 min.
- pH 9 at 50 °C: Samples were taken at 0, 30, 60, 120, 240, 360, 1440 (1 day) and 5760 (4 days) min.

TIER 2:
- pH 4 at 20 °C: Samples were taken at 0, 10, 20, 30, 50, 70 and 120 min.
- pH 7 at 20 °C: Samples were taken at 0, 10, 30, 90, 120, 150, 210, 1140, 1440 (1 day) and 1620 min.
- pH 9 at 20 °C: Samples were taken at 0, 0.04, 0.13, 0.25, 1, 4, 7, 10 and 15 days.

Buffers:

Aqueous buffers were prepared as follows:
- pH 4 (citrate buffer): 23 g of potassium dihydrogen citrate were dissolved in 1 L of water. An aliquot of 0.50 L was mixed with 0.09 L of 0.1 M NaOH and filled up with water to 1 L to give a pH of 4. The pH was checked with a calibrated pH meter to be 4.01 at 20 °C and 3.86 at 50 °C.
- pH 7 (phosphate buffer): 13.6 g of potassium dihydrogen phosphate were dissolved in 1 L of water. An aliquot of 0.50 L was mixed with 0.296 L of 0.1 M NaOH and filled up with water to 1 L to give a pH of 7. The pH was checked with a calibrated pH meter to be 6.78 at 20 °C and 6.73 at 50 °C.
- pH 9 (Borate buffer): 19 g of sodium tetraborate decahydrate were dissolved in 1 L of water. An aliquot of 0.85 L was mixed with 0.15 L of 0.1 M HCl (prepared from 10 M HCl, Merck, 32 %) to give a pH of 9. The pH was checked with a calibrated pH meter to be 9.00 at 20 °C and 9.02 at 50 °C.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: PE centrifuge tubes, 50 mL
- Sterilisation method: The buffers were sterilized after preparation by filtration through pre-assembled sterile 500 mL filters (Nalgene). Sterility of buffers was examined with sterility tests (Cult-Dip-Combi) incubated at approx. 30 °C in the microbiological incubator for approximately 2 days.
- Lighting: No
- Measures to exclude oxygen: Prior to use in the hydrolysis test, each sterilized buffer solution was purged in a gentle stream of nitrogen for approx. 20 min to deplete any dissolved oxygen.
- Details on test procedure for unstable compounds: The LC-MS/MS analysis of collected samples were done immediately due to unstable nature of analyte.

TEST MEDIUM
- Kind and purity of water: LC-MS grade
- Preparation of stock and standard solutions: A stock solution was prepared by accurately weighing 20 mg test substance into a 20 mL volumetric flask using an analytical balance and dissolving it in acetonitrile (resulting concentration of test substance: 1.00 mg/mL, purity was taken into account). A fortification solution with 100 µg/mL, 10 µg/mL and 1 µg/mL were prepared by dilution of the stock solution in acetonitrile.

TIER 1 TEST PROCEDURE
All the test solutions were incubated in the thermostated shaking water bath in dark (under metallic cover) for hydrolysis at 50 °C (± 0.5 °C) for 5 days.

TIER 2 TEST PROCEDURE
The PE tubes were placed in the thermostated walk-in cabinet in the dark for hydrolysis at 20 °C (± 0.5 °C) for 30 days or 90 % hydrolysis of the test substance. Horizontal shaker was used for the continuous mixing of the samples.

Duration:

2 h

pH:

4

Temp.:

20 °C

Initial conc. measured:

0.4 mg/L

Duration:

27 h

pH:

7

Temp.:

20 °C

Initial conc. measured:

0.4 mg/L

Duration:

15 d

pH:

9

Temp.:

20 °C

Initial conc. measured:

0.4 mg/L

Duration:

6 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

0.4 mg/L

Duration:

6 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

0.4 mg/L

Duration:

4 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

0.4 mg/L

Number of replicates:

Hydrolysis at each pH level was performed with three replicate test solutions and one blank for each buffer solution.

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

% Recovery:

2.7

pH:

4

Temp.:

50 °C

Duration:

6 h

Remarks on result:

other:

% Recovery:

5.57

pH:

7

Temp.:

50 °C

Duration:

6 h

% Recovery:

3.79

pH:

9

Temp.:

50 °C

Duration:

4 d

% Recovery:

4.38

pH:

4

Temp.:

20 °C

Duration:

2 h

% Recovery:

6.77

pH:

7

Temp.:

20 °C

Duration:

27 h

% Recovery:

ca. 0

pH:

9

Temp.:

20 °C

Duration:

15 d

pH:

4

Temp.:

50 °C

DT50:

< 30 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

not determinable

Remarks:

due to very fast hydrolysis

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.013 min-1

DT50:

52 min

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.001 min-1

DT50:

1 240 min

Type:

(pseudo-)first order (= half-life)

pH:

4

Temp.:

20 °C

Hydrolysis rate constant:

0.053 min-1

DT50:

13 min

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

0.013 min-1

DT50:

53.5 min

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0.195 d-1

DT50:

3.55 d

Type:

(pseudo-)first order (= half-life)

Details on results:

TIER 1 RESULTS
The test substance was very hydrolytically unstable and disintegrated quickly within 24 hours of incubation at 50 °C. The degradation of the test substance was very fast at pH 4 buffer system (t1/2 = < 30 min) and in pH 7 buffer system (t1/2 = 52 min) as well in comparison to pH 9 borate buffer (t1/2 = 1240min). The recoveries observed for extracts of the different pH values and hydrolysis periods were always < 10 % of the initial concentration.

TIER 2 RESULTS
The recoveries observed for extracts of pH 4 collected at test start and after a hydrolysis period of 120 min were <10 % of the initial concentration of the test substance. The hydrolytic degradation followed a first order kinetic with r2 = 0.9919. The half-life time observed was about 13 minutes and rate constant was about 0.0534 per minute. The recoveries observed for extracts of pH 7 collected at time-0 and after a hydrolysis period of 1620 min were <10 % of the initial concentration of the test substance. Within 10 min of hydrolysis approx. 55% of the analyte was degraded. The degradation of the test substance does not fit with first order kinetic (r2 = 0.6428). The recoveries observed for extracts of pH 9 collected after a hydrolysis period of 4 days indicated the degradation of approx. 53%. However, at day 7, reoccurrence of the test substance was observed. This increase in the concentration of the test substance after 7 days might be inferred as the analyte formed complex with boron present in pH 9 borate buffer. Thus, the kinetic of degradation was calculated until day 4 indicating 1st order of degradation (r2 = 0.989). The half-life time observed was about 3.5 days, and the rate constant was about 0.195 per day.

Validity criteria fulfilled:

not specified

Description of key information

The test substance is hydrolytically unstable in pH 4 and 7 buffers at 20 °C with half lives of 13 and 54 minutes, respectively. The test substance is more stable in pH 9 buffer with a determined half-life of 3.5 days.

Key value for chemical safety assessment

Half-life for hydrolysis:

54 min

at the temperature of:

20 °C

Additional information

The hydrolytic stability of the test substance was studied in aqueous solutions buffered to pH values of 4, 7 or 9 and incubated at temperatures of 50°C (Tier 1) and 20 °C (Tier 2) in accordance with OECD TG 111 and in compliance with GLP-criteria (EAG Inc., 2018). The nominal concentration of the test substance in the hydrolysis media was 0.4 mg/L, which is below its water solubility of 0.634 mg/L. Test solutions were incubated under sterile conditions, in darkness. Aliquots of the hydrolysis samples were collected, diluted and immediately analysed by LC-MS/MS. At each pH, samples were analysed at test initiation and regularly throughout the test up to 6 hours for pH 4, 27 hours for pH 7 and 15 days for pH 9.  Final recoveries of the test substance were in almost all cases < 10%. Only for pH 9 extracts at 20 °C, the recovery was about 47% after 4 days; after 7 days, reoccurence of the test substance was observed due to complexing with boron present in the borate buffer. The rate of hydrolysis was dependent upon pH, with increasing hydrolysis rate at lower pH values (and higher temperature). At pH 9, the test substance was most stable with a half-life of approximately 3.6 days at 20 °C (after 4 days). Half-lives at pH 7 and 4 were determined to be 54 and 13 minutes, respectively, at 20 °C.