Methomyl

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

other: U.S. EPA Subdivision D, 63-13

Deviations:

no

GLP compliance:

no

Specific details on test material used for the study:

- Substance name: Methomyl
- Purity: Not reported

Radiolabelling:

no

Analytical monitoring:

no

Buffers:

- pH: 5, 7, 9

Duration:

30 d

pH:

5

Duration:

30 d

pH:

7

Duration:

30 d

pH:

9

Number of replicates:

One

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

Key result

pH:

9

DT50:

30 d

Key result

Remarks on result:

other: The test substance was stable in sterile distilled water for 30 days at pH 5 and 7

Validity criteria fulfilled:

not specified

Conclusions:

The test substance was stable in sterile distilled water for 30 days at pH 5 and 7, but decomposed with a half-life of 30 days at pH 9.

Executive summary:

The objective of the study was to determine the stability of the test substance in sterile distilled water at pH levels of 5, 7 and 9, following the guideline U.S. EPA 63-13.

The test substance was stable in sterile distilled water for 30 days at pH 5 and 7, but decomposed with a half-life of 30 days at pH 9.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Purity: 99.8%

Radiolabelling:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals:
pH 4 and 7, 30 and 40 °C: Days 0, 3, 7, 14, 21, 25, 28, 31
pH4 60 °C: Days 0, 1, 3, 4, 8, 11, 15, 18, 31
pH7 60 °C: Days 0, 0.9, 1.2, 2, 3, 4, 7, 8, 11
pH9 25 °C: Days 0, 1, 2, 5, 7, 16, 21, 30
pH9 35 °C: Days 0, 0.8, 1, 2, 3, 4, 6, 7, 12
pH9 45 °C: Days 0, 0.1, 0.2, 0.3, 0.5, 1, 1.3, 2, 3

- Sampling method: The test system solutions were aliquoted from the volumetric flasks to HPLC vials and analyzed directly by HPLC. Individual vials were removed from incubation at each time point; 1-mL aliquots of the test solution were removed, added to HPLC vials and analyzed by HPLC directly.

- Sampling intervals/times for pH: The pH of each buffer solution was measured at the time of preparation. The pH of each test sample solution was measured after addition of the test substance and at the end of the hydrolysis testing.

- Sampling intervals/times for sterility check: At the initiation and termination of all tests, sterility of the test solutions was verified using 3M™ Petrifilm™, with the exception of initiation of the pH 9 tests at 25 °C and 35 °C, and the termination of the pH 7 at 60 °C test. An aliquot of each test solution (1 mL) was applied on a Petrifilm™ and incubated at 30 °C for at least 3 days following completion of the experimental test. The incubated Petrifilms™ were counted for potential contaminated biological species. Microbial enumeration to show sterility was not completed at initiation of the pH 9 tests at 25 °C and 35 °C, or the termination of the pH 7 at 60 °C test. Sterility testing was completed at termination for the pH 9 tests and showed sterility under the test conditions. For the pH 7, 60 °C test, the termination samples were removed from storage (freezer) and microbial enumeration was performed and showed sterility. In these cases, sterility was shown after the end of the study showing no contamination of the samples. Therefore, there was no negative impact due to this deviation.

- Sample storage conditions before analysis: All samples were analyzed on the sampling day when possible. Samples were stored frozen after the initial analysis.

Details on test conditions:

A preliminary test (Tier 1) was conducted. A [14C]methomyl stock solution was prepared by adding 29 μL of R-12438-A (MM-12445-00001) to a 25-mL volumetric flask and bringing the flask volume with 0.01 M pH 4 buffer. This solution was given the ABC designation of R-12445-A with a concentration of 1.15 mg/L. A [14C]methomyl stock solution was prepared by adding 29 μL of R-12438-A (MM-12445-00001) to a 25-mL volumetric flask and bringing the flask volume with 0.01 M pH 7 buffer. This solution was given the ABC designation of R-12445-B with a concentration of 1.09 mg/L. The preliminary test was conducted from 24 June to 29 June 2015 at pH 4 and pH 7. Greater than 10% hydrolysis of the test substance was observed at both pHs; therefore, a Tier 2 definitive test was conducted.

For the Definitive test (Tier 2) Test solutions were prepared by adding aliquots of the 849.0 μg/mL stock solution to volumetric flasks. The flasks were then brought to volume with the appropriate buffer. If necessary, the stock solution was concentrated under nitrogen so the amount of organic solvent in all test solutions was ≤ 0.5%. These test solutions were then aliquoted with no headspace into individual autoclaved amber borosilicate vials with sterilized PTFE lined caps. The individual hydrolysis test vessels were wrapped in aluminum foil and placed into the appropriate incubators. On Day 0, the test system solutions were aliquoted from the volumetric flasks to HPLC vials and analyzed directly by HPLC. Individual vials were removed from incubation at each time point; 1-mL aliquots of the test solution were removed, added to HPLC vials and analyzed by HPLC directly. When sampling was complete, the amber test sample vials were stored frozen. The sampling schedule was described above.

Identification of hydrolysis products (Tier 3) was conducted. Metabolites were chromatographically separated and assigned by HPLC by comparing retention times with authentic reference standards. High-performance liquid chromatography/ultra-violet detection (HPLC/UV) analysis using a different column packing material was used as the confirmatory method.

Duration:

31 d

pH:

4

Temp.:

30 °C

Duration:

31 d

pH:

4

Temp.:

40 °C

Duration:

31 d

pH:

4

Temp.:

60 °C

Duration:

31 d

pH:

7

Temp.:

30 °C

Duration:

31 d

pH:

7

Temp.:

40 °C

Duration:

31 d

pH:

7

Temp.:

60 °C

Duration:

30 d

pH:

9

Temp.:

25 °C

Duration:

12 d

pH:

9

Temp.:

35 °C

Duration:

3 d

pH:

9

Temp.:

45 °C

Number of replicates:

2

Positive controls:

no

Statistical methods:

Mean results were calculated from the results of individual replicates. Where assessment of the variability within replicates was required, mainly for analytical data, coefficients of variance were calculated.

Preliminary study:

In the preliminary experiment, methomyl was shown to be hydrolytically unstable at pH 4 and 7, and prior information about the hydrolysis of the test substance at pH 9 led to all pH levels being tested in the definitive experiment.

Transformation products:

yes

No.:

#1

No.:

#2

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

Degradation in all pH buffers proceeded primarily via hydrolysis of the carbamate ester of methomyl to form IN-X1177 and then the formation of acetonitrile (ACN).

Key result

pH:

4

Temp.:

30 °C

Hydrolysis rate constant:

0.002 d-1

DT50:

319 d

Type:

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

Key result

pH:

4

Temp.:

40 °C

Hydrolysis rate constant:

0.007 d-1

DT50:

100 d

Type:

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

Key result

pH:

4

Temp.:

60 °C

Hydrolysis rate constant:

0.079 d-1

DT50:

8.79 d

Type:

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

Key result

pH:

7

Temp.:

30 °C

Hydrolysis rate constant:

0.003 d-1

DT50:

273 d

Type:

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

Key result

pH:

7

Temp.:

40 °C

Hydrolysis rate constant:

0.014 d-1

DT50:

50 d

Type:

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

Key result

pH:

7

Temp.:

60 °C

Hydrolysis rate constant:

0.25 d-1

DT50:

2.81 d

Type:

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

Key result

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.051 d-1

DT50:

13.7 d

Type:

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

Key result

pH:

9

Temp.:

35 °C

Hydrolysis rate constant:

0.25 d-1

DT50:

2.77 d

Type:

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

Key result

pH:

9

Temp.:

45 °C

Hydrolysis rate constant:

0.94 d-1

DT50:

0.734 d

Type:

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

pH	Temperature (degC)	Maximum Amount of Metobilte Detected at Teimpoint (expressed as % AR)
		IN-X1177	ACN
4	30	4.1 (Day 31)	3.3 (Day 28)
4	40	11.6 (Day 31)	7.4 (Day 28)
4	60	41.2 (Day 18)	36.3 (Day 31)
7	30	11.3 (Day 31)	1.4 (Day 14)
7	40	36.0 (Day 31)	1.6 (Day 25)
7	60	90.7 (Day 11)	1.6 (Day 7)
9	25	78.2 (Day 30)	1.5 (Day 16)
9	35	94.1 (Day 12)	1.5 (Day 3)
9	45	92.9 (Day 3)	1.5 (Day 0.2)

 

Validity criteria fulfilled:

yes

Conclusions:

Methomyl was unstable at all pH and temperature conditions; however, hydrolysis occurred at a more rapid rate at higher temperatures across the pH range tested. Based on these results, methomyl would be expected to hydrolyze in the environment.

Executive summary:

The hydrolysis of [14C] methomyl was studied in sterile aqueous solutions buffered at pH 4 (0.01 M phthalate), 7 (0.01 M phosphate), and 9 (0.01 M borate). The tests were conducted at three different temperatures: pH 4 and 7 (30°C, 40°C, and 60°C) and pH 9 (25°C, 35°C, and 45°C). The concentration of the test substance was 0.947 to 1.15µg/mL (approximately 1 ppm (or mg/L)). In the preliminary experiment, methomyl was shown to be hydrolytically unstable at pH 4 and 7, and prior information about the hydrolysis of the test substance at pH 9 led to all pH levels being tested in the definitive experiment. Buffer solutions at pH 4, 7, and 9 were fortified with test substance, incubated at temperatures ranging from 25 to 60 °C, and analyzed at various intervals by High Performance Liquid Chromatography (HPLC) with an in-line radiochemical detector and liquid scintillation counting (LSC).

 

The material balance was quantitative for all samples and was in the range of 89.8 to 106.6% applied radioactivity (% AR).

 

Degradation in all pH buffers proceeded primarily via hydrolysis of the carbamate ester of methomyl to form IN-X1177 and then the formation of acetonitrile (ACN). Methomyl and metabolites, IN-X1177 and ACN, were assigned by comparison of the HPLC retention times with respective reference standards. ACN was confirmed through a secondary HPLC method, as well as through volatilization experiments.

 

The percentage of parent methomyl was plotted against time for each pH level and temperature, and the DT50values were determined using SFO (single first order) kinetics, which displayed a good fit to the data. At pH 4, the DT50 values were 319, 100, and 8.79 days at 30, 40, and 60°C, respectively.  At pH 7, the DT50 values were 273, 50.0, and 2.81 days at 30, 40, and 60°C, respectively. At pH 9, the DT50 values were 13.7, 2.77, and 0.734 days at 25, 35, and 45°C, respectively.  

 

This study demonstrated that methomyl was unstable at all pH and temperature conditions; however, hydrolysis occurred at a more rapid rate at higher temperatures across the pH range tested. Based on these results, methomyl would be expected to hydrolyze in the environment.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
Hydryolysis	Tested at pH 5 and pH 9	Stable at pH = 5 DT50 = 30 days at pH = 9	EPA 63-13	2
Hydrolysis	Tested at pH 5, 7, and 9	Unstable at all pH and temperature conditions. Hydrolysis occurred at a more rapid rate at higher temperatures across the pH range tested. pH 4, the DT50 values were 319, 100, and 8.79 days at 30, 40, and 60°C, respectively. pH 7, the DT50 values were 273, 50.0, and 2.81 days at 30, 40, and 60°C, respectively. pH 9, the DT50 values were 13.7, 2.77, and 0.734 days at 25, 35, and 45°C, respectively	OECD 111 OPPTS 835.2120	1

Key value for chemical safety assessment

Half-life for hydrolysis:

273 d

at the temperature of:

30 °C