Thiram

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 June 1989 - 11 January 1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: US EPA Ref.: 161-1, Hydrolysis Studies

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

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

Temp.:

25 °C

Initial conc. measured:

7.28 other: ppm

Duration:

8 d

pH:

7

Temp.:

25 °C

Initial conc. measured:

7.91 other: ppm

Duration:

16 h

pH:

9

Temp.:

25 °C

Initial conc. measured:

7.15 other: ppm

Number of replicates:

At least two vessels were prepared for each time point. Each vessel was sampled only once (in duplicate samples).

Positive controls:

no

Negative controls:

no

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

For details on pH measurements and recoveries of initial radioactivities see attachment.

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.
Due to the presented results, hydrolysis process can contribute to degradation of Thiram in aquatic systems.
Validity and quality criteria can be considered as fulfilled.

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. 

Description of key information

Hydrolysis is a relevant degradation pathway for tetramethylthiuram disulfide (CAS No. 137-26-8) in aquatic systems: DT50 (pH 7) = 3.5 days (25 °C, EPA Guideline Subdivision N 161-1).

Key value for chemical safety assessment

Half-life for hydrolysis:

3.5 d

at the temperature of:

25 °C

Additional information

One study determining the hydrolysis half-life of tetramethylthiuram disulfide (CAS No. 137-26-8) is available. 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 25 °C and pH 5, 7 and 9. The half-lives determined were 68.5 days, 3.5 days and 6.9 hours at pH 5, 7 and 9, respectively. Hydrolysis in alkaline and neutral conditions took place at a faster rate than under acidic conditions. The main breakdown product was CS2.

 

In conclusion, hydrolysis may be a relevant degradation pathway for the substance in aquatic systems.