Thiophanate-methyl

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 1981-04-13 to 1981-05-25

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Qualifier:

according to guideline

Guideline:

other: German Biologische Bundesanstalt (BBA) Guideline Nr. 55 Teil I

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

Version / remarks:

1982

Deviations:

no

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

At each sampling time, two flasks were sampled and 5 µL of each test solution were injected into the HPLC.

Buffers:

Clark-Lubs buffer solution for pH 5 and 9, and Sorensen buffer solution for pH 7
pH 5: 50 mL 0.2 M potassium hydrogen phthalate, 23.85 mL 0.2 N sodium hydroxide, 126.15 mL water
pH 7: 4.0 mL M/15 potassium dihydrogen phosphate, 6.0 mL M/15 disodium hydrogen phosphate
pH 9: 50 mL 0.2 N boric acid + 0.2 M potassium chloride, 21.3 mL 0.2 N sodium hydroxide, 128.70 mL water

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: 50 mL Erlenmeyer flask closed with stoppers.
- Sterilisation method: The buffer solutions were passed through a membrane filter (0.2 µm) for sterilization. All glasswares were sterilized by heating at 150 °C for 30 min before use.
- Measures taken to avoid photolytic effects: The test solutions were kept in dark incubators.

Duration:

8 min

pH:

9

Temp.:

65 °C

Initial conc. measured:

9.62 mg/L

Duration:

2 h

pH:

9

Temp.:

45 °C

Initial conc. measured:

9.82 mg/L

Duration:

96 h

pH:

9

Temp.:

22 °C

Initial conc. measured:

9.98 mg/L

Duration:

3.5 h

pH:

7

Temp.:

65 °C

Initial conc. measured:

9.92 mg/L

Duration:

137 h

pH:

7

Temp.:

45 °C

Initial conc. measured:

9.93 mg/L

Duration:

33 d

pH:

7

Temp.:

22 °C

Initial conc. measured:

9.77 mg/L

Duration:

168 h

pH:

5

Temp.:

65 °C

Initial conc. measured:

9.98 mg/L

Duration:

35 d

pH:

5

Temp.:

45 °C

Initial conc. measured:

10.01 mg/L

Duration:

35 d

pH:

5

Temp.:

22 °C

Initial conc. measured:

10.06 mg/L

Number of replicates:

Two replicate flasks were prepared.

Positive controls:

no

Negative controls:

no

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on hydrolysis and appearance of transformation product(s):

#1 = MBC
#2 = AV-1951
#3 = 2-AB

% Recovery:

>= 22.5 - <= 92.2

pH:

9

Temp.:

65 °C

Duration:

>= 0 - <= 8 min

% Recovery:

>= 21.2 - <= 98.2

pH:

9

Temp.:

45 °C

Duration:

>= 0 - <= 2 h

% Recovery:

>= 6.5 - <= 99.8

pH:

9

Temp.:

22 °C

Duration:

>= 0 - <= 96 h

% Recovery:

>= 21.8 - <= 99.2

pH:

7

Temp.:

65 °C

Duration:

>= 0 - <= 3.5 h

% Recovery:

>= 16.7 - <= 99.3

pH:

7

Temp.:

45 °C

Duration:

>= 0 - <= 137 h

% Recovery:

>= 59.6 - <= 97.7

pH:

7

Temp.:

22 °C

Duration:

>= 0 - <= 33 d

% Recovery:

>= 14.6 - <= 99.8

pH:

5

Temp.:

65 °C

Duration:

>= 0 - <= 168 h

% Recovery:

>= 61.3 - <= 100.1

pH:

5

Temp.:

45 °C

Duration:

>= 0 - <= 35 d

% Recovery:

>= 98.1 - <= 100.6

pH:

5

Temp.:

22 °C

Duration:

>= 0 - <= 35 d

Key result

pH:

7

Temp.:

12 °C

Hydrolysis rate constant:

0 h-1

DT50:

101.85 d

Type:

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

Remarks on result:

other: extrapolated value

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.041 h-1

DT50:

0.7 d

Type:

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

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

36 d

Type:

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

pH:

5

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

867 d

Type:

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

Details on results:

TEST CONDITIONS
During the dark incubation, the pH values of the solution were not changed and the evidence for microbial contamination was not observed. The amounts of test item and hydrolysis products were determined by the HPLC method.

MAJOR TRANSFORMATION PRODUCTS
At pH 5:
- 22 °C: 98.1 % TM after 35 days
- 45 °C: 61.3 % TM, 29.2 % MBC, 2.7 % AV-1951 after 35 days
- 65 °C: 14.6 % TM, 68.2 % MBC, 2.4 % AV-1951, 12.4 % 2-AB after 168 hours
At pH 7:
- 22 °C: 59.6 % TM, 28.6 % MBC, 8.1 % AV-1951 after 33 days
- 45 °C: 16.7 % TM, 67.2 % MBC, 11.2 % AV-1951 after 137 hours
- 65 °C: 21.8 % TM, 66.7 % MBC, 8.1 % AV-1951 after 3.5 hours
At pH 9:
- 22 °C: 6.5 % TM, 58.7 % MBC, 24.9 % AV-1951 after 96 hours
- 45 °C: 21.2 % TM, 59.8 % MBC, 15.8 % AV-1951 after 2 hours
- 65 °C: 22.5 % TM, 61.5 % MBC, 11.4 % AV-1951 after 8 min

The hydrolysis rate constant and half-life at pH 7 and 12 °C (environmentally relevant conditions) was extrapolated from the obtained data. It was calculated that under environmental conditions the test item would have a hydrolysis constant of 0.00028356 h-1 and a DT50 of 2444.44 h or 101.85 d.

Experiment A

In Experiment A, the hydrolysis products of TM in the buffer solutions with different pH were identified by chromatographic and instrumental analyses. Three kinds of TM solutions were incubated at 65 °C. At three different pH (5, 7 and 9), the major peaks P3 and P1 of hydrolysis products agreed with those of standards MBC and AV-1951, respectively. Another peak P2 found in the solutions of pH 5 and 9 matched with that of standard 2-AB. On the other hand, TLC Rf values of two compounds P4 and P1 extracted at pH 2 matched with those of standards TM and AV-1951, respectively. In the second extract at pH 6, there was one compound P3 of which Rf value was the same as that of standard MBC. The Rf value of the compound P2 detected in the final aqueous fraction agreed with that of standard 2-AB. The spectra of recovered TM and these three products were identical to each standard compound showing the parent peaks of 284, 133, 191 and 342 for P1, P2, P3 and P4, respectively. Thus, it was concluded that the hydrolysis products of TM in aqueous solution were MBC, AV-1951 and 2-AB. Any of the other compounds was not detected in the test solutions.

 

Experiment B

Based on the above results, the rate of the hydrolysis of TM was investigated at pH 5, 7 and 9 and at 22, 45 and 65 °C. The concentration of TM was decided as 10 ppm corresponding to about half of its water solubility (21.8 ppm). During the dark incubation, the pH values of the solution were not changed and the evidence for microbial contamination was not observed. The amounts of TM and hydrolysis products were determined by the HPLC method. As good recoveries of TM equivalents were obtained under all conditions, it can be said that the compounds other than these three products were present in negligible amounts, if at all. MBC was a major product under all conditions. Although it was not confirmed fully in Exp. B, the compound will be further degraded to 2-AB as shown in Exp. A. AV-1951 was mainly found in pH 9 solution, and 2-AB was only found in pH 5 solution at 65 °C. From other experiments, it is known that AV-1951 is also decomposed to MBC in water.

The hydrolysis constants (k) and half-lives (T) of TM were calculated by the least-squares method. The hydrolysis rate of TM depended on temperatures and pH values. TM was most unstable under the condition of 65 °C and pH 9 with a half-life of ca. 3.9 min. In the solution of pH 5 at 22 °C, to the contrary, TM was most stable with a half-life of ca. 1179 days. The half-lives of TM at 25 °C were obtained by interpolation using Arrhenius equation and were 867, 36 and 0.7 days at pH 5, 7 and 9, respectively.

Validity criteria fulfilled:

yes

Conclusions:

The half-life of the test item at 25 °C was determined to be 867, 36 and 0.7 days at pH 5, 7 and 9, respectively. Under environmental conditions (pH 7 and 12 °C) the test item's hydrolysis constant was calculated to be 0.00028356 h-1 and the DT50 to be 2444.44 h or 101.85 d.

Executive summary:

The hydrolysis of the test item in buffer solutions was studied in accordance with BBA Merkblatt Nr.55 Teil I. Although this study was conducted prior to the issuance of Guidelines 40 CFR 161-1 (October, 1982), the study conforms to those Guidelines where applicable. Firstly, it was clarified that the major hydrolysis product was MBC and minor products were AV-1951 and 2-AB. The separation, identification and detection of these products was performed by HPLC and TLC and mass spectrometry. Secondary, the disappearance of the test item and the formations of MBC, AV-1951 and 2-AB at pH 5, 7 and 9 and at 22, 45 and 65 °C was investigated. The half-life of the test item obtained by interpolation at 25 °C were 867, 36 and 0.7 days at pH 5, 7 and 9, respectively. The test item was most unstable under the condition of pH 9 and 65 °C with a half-life of 3.9 minutes. Under environmental conditions (pH 7 and 12 °C) the test item's hydrolysis constant was calculated to be 0.00028356 h-1 and the DT50 to be 2444.44 h or 101.85 d.

 

Description of key information

The test item showed to be stable to hydrolysis at ambient temperature (22 °C) and pH-values (5 – 7). The half-life of the test item at 25 °C was determined to be 867, 36 and 0.7 days at pH 5, 7 and 9, respectively. Under environmental conditions (pH 7 and 12 °C) the test item's hydrolysis constant was calculated to be 0.00028356 h-1 and the DT50 to be 2444.44 h or 101.85 d.

Key value for chemical safety assessment

Half-life for hydrolysis:

101.85 d

at the temperature of:

12 °C

Additional information

The hydrolysis of the test item in buffer solutions was studied in accordance with BBA Merkblatt Nr.55 Teil I. Although this study was conducted prior to the issuance of Guidelines 40 CFR 161-1 (October, 1982), the study conforms to those Guidelines where applicable. Firstly, it was clarified that the major hydrolysis product was MBC and minor products were AV-1951 and 2-AB. The separation, identification and detection of these products was performed by HPLC and TLC and mass spectrometry. Secondary, the disappearance of the test item and the formations of MBC, AV-1951 and 2-AB at pH 5, 7 and 9 and at 22, 45 and 65 °C was investigated. The half-life of the test item obtained by interpolation at 25 °C were 867, 36 and 0.7 days at pH 5, 7 and 9, respectively. The test item was most unstable under the condition of pH 9 and 65 °C with a half-life of 3.9 minutes. Under environmental conditions (pH 7 and 12 °C) the test item's hydrolysis constant was calculated to be 0.00028356 h-1 and the DT50 to be 2444.44 h or 101.85 d.