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Environmental fate & pathways

Hydrolysis

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Endpoint:
hydrolysis
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
GLP - Guideline study, tested with the source substance tetramethylthiuram disulfide (CAS No. 137-26-8). In accordance to the ECHA guidance document “Practical guide 6: How to report read-across and categories (March 2010)”, the reliability was changed from RL1 to RL2 to reflect the fact that this study was conducted on an read-across substance
Qualifier:
according to guideline
Guideline:
other: US EPA Ref.: 161-1, Hydrolysis Studies
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Samplings were performed at following intervals:
- for pH 5: 0, 3, 7, 14, 23 and 30 days
- for pH 7: 0, 1, 2, 4, 6 and 8 days
- for pH 9: 0, 0.5, 1, 2, 4, 6, 8, 10 and 16 hours
Only one set of treated samples was prepared;
each vessel was sampled only once.
Buffers:
- pH 5: 0.01 M acetate buffer
- pH 7: 0.006 M phosphate buffer
- pH 9: 0.003 M borate buffer
Details on test conditions:
TEST SYSTEM
Test vessels: Oak Ridge Teflon centrifuge tubes (25.5 x 92 mm, Nalge Company) with a Nalgene screw closure, Teflon-lined septum, 0.2 µm Nylon filter
- Sterilisation method: Prior to use, all glassware, Teflon vessels, and septa were sterilized in a pressure cooker at 121°C for 30 minutes.
All buffer were filtered through a 0.2 µm nylon filter prior to use.

TEST MEDIUM
- Kind of water: deionized water
- Preparation of test medium: An aliquot of 100 µL stock solution of 14C-Thiram (2 mg/mL) was added to each test tube. The solvent was removed under a stream of nitrogen. Then 20 mL of the buffer solution was added to each test tube, to achieve a nominal 14C-Thiram concentration of 10 ppm. The samples were sonicated for up to 5 minutes to redissolve the 14C-Thiram in the appropriate buffer.
- Renewal of test solution: no
- Identity and concentration of co-solvent: not reported
Duration:
30 d
pH:
5
Initial conc. measured:
10 mg/L
Duration:
8 d
pH:
7
Initial conc. measured:
10 mg/L
Duration:
16 h
pH:
9
Initial conc. measured:
10 mg/L
Number of replicates:
Only one set of treated samples was prepared;
each vessel was sampled only once
Transformation products:
yes
No.:
#1
pH:
5
Temp.:
25 °C
Hydrolysis rate constant:
0.01 d-1
DT50:
68.5 d
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.2 d-1
DT50:
3.5 d
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
2.42 d-1
DT50:
6.9 h
Validity criteria fulfilled:
yes
Conclusions:
The hydrolysis of Thiram occurs in alkaline and neutral media much more rapidly than under acidic condition.
The major hydrolysis product was Carbon disulfide (CS2). The material balance for the buffered samples was > 90% of the initial radioactivity.
The amount of the other breakdown products isolated from the chloroform extracts did not exceed 10% of the initial radioactivity.
Executive summary:

Materials and methods: The stability of 14C-labelled Thiram (10 ppm) in sterile aqueous buffers maintained at three pH levels (5, 7 and 9) was studied. Samples were incubated at 25 °C in the dark and under sterile conditions.

The tests were performed for 30 days at pH 5, 8 days at pH 7 and 16 hours at pH 9.

Prior to use, all glassware, Teflon vessels and septa were sterilized in a pressure cooker at 121°C for 30 min to minimize biodegradation.

All buffers were filtered through a 0.2-µm nylon filter. After filtration, the sterility of the buffers was checked with Petrifilm 6400 aerobic count plates.

Results and discussion: The hydrolysis of Thiram was analysed in pH 5, pH 7 and pH 9 at a concentration of 7.28 ppm, 7.91 ppm and 7.15 ppm of 14C-Thiram, respectively. Under alkaline or neutral conditions, 14C -Thiram was rapidly hydrolysed. The majority of the radioactivity was continuously released as volatiles during the study. The major breakdown product for all buffers was identified as volatile CS2. The material balance for all samples was greater than 90% after purging. The volatiles contained in the pH 9 were released particularly upon acidification.

Further breakdown products were isolated in the chloroform extracts; however, none comprised more than 5% of the initial radioactivity during the study. The remaining buffer solution after chloroform extraction contained less than 10% of the initial radioactivity over the time studied for pH 5 and pH 7. The extracted buffer solution at pH 9 contained up to 35% of the initial radioactivity. After acidification of the extracted pH 9 solution, most of the radioactivity was released as 14C CS2. 

Endpoint:
hydrolysis
Type of information:
calculation (if not (Q)SAR)
Remarks:
Migrated phrase: estimated by calculation
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Scientifically accepted calculation method
Principles of method if other than guideline:
Calculated using HYDROWIN v2.00 , a subroutine of the computer program EPI Suite™ (Estimation Program Interface for Windows, version 4.0. Syracuse Research Corporation, Syracuse, NY, USA) U.S. Environmental Protection Agency, OPPT

pH5   less than one day to several weeks

pH7   less than one day to several days

pH9   less than one day

Description of key information

Hydrolysis may be a relevant degradation pathway for disulfiram in aquatic systems (half-lives 68.5 days, 3.5 days and 6.9 hours under acidic, neutral and alkaline conditions respectively)

Key value for chemical safety assessment

Additional information

No data on hydrolysis of disulfiram (CAS No. 97-77-8) are available. Therefore, a conclusion based on data from an analogue substance had to be drawn. Hydrolysis of tetramethylthiuram disulfide (CAS No.137-26-8), substance structurally and composition related to tetraethylthiuram disulfide, was investigated in one study. This test was conducted according to EPA’s Pesticide Assessment Guidelines, Series 161-1, Hydrolisis Studies (1988), under GLP conditions.14C-thiram was tested at pH 5, 7 and 9, and the half-lives determined, being 68.5 days, 3.5 days and 6.9 hours respectively. Hydrolysis in alkaline and neutral conditions took place at a faster rate than under acidic conditions. The main breakdown product was CS2.

The results from the HYDROWIN v2.00 program support these findings, as the hydrolysis of disulfiram is predicted to occur faster under neutral and alkaline conditions (less than one day to several days and less than one day, respectively).