ethametsulfuron-methyl (ISO); methyl 2-[(4-ethoxy-6-methylamino-1,3,5-triazin-2-yl)carbamoylsulfamoyl]benzoate

Hydrolysis

Administrative data

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2010

Report date:

2010

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: Society for Environmental Toxicology And Chemistry (SETAC), Procedures for Assessing the Environmental Fate and Ecotoxicology of Pesticides (March 1995)

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Reference substance 002

Cas Number:

97780-06-8

Test material form:

solid

Details on test material:

Purity: 85-99%

Specific details on test material used for the study:

[Phenyl(U) label-14C] test substance (Lot Number 3597150)
Radiochemical purity and specific activity: 97.1% and 39.55 µCi/mg, respectively

[Triazine(U) label-14C] test substance (Lot Number 3697154)
Radiochemical purity and specific activity: 97.0% and 49.61 µCi/mg, respectively

Radiolabelling:

yes

Study design

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: 10 and 25°C at pH 4: Samples were immediately analyzed after the test substance was placed into the test vessels (Day 0) and after 1, 3, 4, 7, 15, 21, and 30 days.
35°C at pH 4: Samples were immediately analyzed after the test substance was placed into the test vessels (Day 0) and after 1, 2, 4, and 6 hours and at 1, 2, 3, and 6 days.
50°C at pH 4, pH 7 and 9: Samples were immediately analyzed after the test substance was placed into the test vessels (Day 0) and after 1, 2, and 5 days.
60°C at pH 7 and 9: Samples were immediately analyzed after the test substance was placed into the test vessels (Day 0) and after 1, 2, 3, 4, 7, 10, and 14 days.
70°C at pH 7 and 9: Samples were immediately analyzed after the test substance was placed into the test vessels (Day 0) and after 1, 2, 3, 4, and 7 days.
- Sampling intervals/times for pH measurements: The pH of each buffer solution was measured at the time of preparation and after addition of the test item. The pH was also documented at each sampling point for all samples.
- Sampling intervals/times for sterility check: For the preliminary (Tier 1) systems (pH 4, 7, and 9 at 50°C), sterility was verified for each site of labelling and pH at Day 0. For all subsequent (Tier 2) systems, sterility was verified at Day 0 and at the end of the incubation period.
- Sample storage conditions before analysis: All samples were analyzed as soon as possible after sampling. If samples were not analyzed immediately, they were stored at ca -20°C until analysis could be performed.
- Sampling methods for the volatile compounds, if any: Trapping of CO2 was performed using two incubated hydrolysis vessels (one for each 14[C]-label position). These vials were incubated for the duration of the study and kept under gas-tight conditions. At the end of the incubation period, one hydrolyzed sample from triazine and one hydrolyzed sample from phenyl labeled test solution were sparged for 30 minutes through a trap containing 20 mL of ethylene glycol and a trap in series containing 30 mL of 1N KOH.

Buffers:

- pH: This study was conducted in sterile solutions buffered at pH 4, 7, and 9.
- Type and final molarity of buffer: A buffer concentration of 0.02 M was selected in order to minimize possible catalytic effects.
- Composition of buffer
A 0.02 M pH 4 buffer solution was prepared by titration of the 0.02 M citric acid solution with the 0.02 M sodium citrate solution to a final pH of 4.0 ± 0.1. The pH of the buffer solution was again verified to be pH 4.0 ± 0.1 after sterilization.
A 0.02 M pH 7 buffer solution was prepared by titration of the 0.02 M tris base/maleic acid solution with the 0.02 M sodium hydroxide solution to a final pH of 7.0 ± 0.1. The pH of the buffer solution was again verified to be pH 7.0 ± 0.1 after sterilization.
A 0.02 M pH 9 buffer solution was prepared by titrating the 0.02 M sodium tetraborate solution with the 0.02 M boric acid solution to a final pH of 9.0 ± 0.1. The pH of the buffer solution was again verified to be pH 9.0 ± 0.1 after sterilization.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: glass hydrolysis vessels (ca. 7 mL capacity) with tightly sealed caps.
- Sterilisation method: All glassware, incubation vessels and associated equipment were sterilized by autoclaving.
- Details of traps for volatile, if any: For each temperature/pH/radiolabel system, duplicate sterile 20 mL vessels were also filled with 15 mL of test solution. These vessels were sealed with Teflon-lined silicon septa screw-caps.
- Indication of the test material adsorbing to the walls of the test apparatus: No significant adsorption and loss of radioactivity due to adsorption to apparatus at any pH or temperature was observed.

TEST MEDIUM
- Volume used/treatment: 7 mL of sterile pH 4, 7, or 9 buffer containing approximately 0.28 µg/mL test substance
- Kind and purity of water: Milli-Q water
- Preparation of test medium: A stock solution of [triazine 14C]-test substance was prepared by dissolving the entire radiolabeled test item in 3.1 mL of acetonitrile. The calculated concentration of the resulting stock solution was 361 µg/mL based on the dpm counts and the specific activity. A stock solution of [phenyl 14C]-test substance was prepared by dissolving the entire radiolabeled test item in 3.36 mL of acetonitrile. The calculated concentration of the resulting stock solution was 222.5 µg/mL based on the dpm counts and the specific activity.
- Identity and concentration of co-solvent: The final concentration of acetonitrile co-solvent was <1%

Duration of test

Duration:

30 d

Initial conc. measured:

0.28 other: µg/mL

Remarks:

pH 4, 7, and 9 which were incubated at either 10 ± 1°C, 25 ± 1°C, 35 ± 1°C, 50 ± 1°C, 60 ± 1°C, or 70 ± 1°C

Number of replicates:

Two

Results and discussion

Transformation products:

yes

Identity of transformation products

Identity of transformation products 1

No.:

#1

Reference

Reference substance name:

Unnamed

Identity of transformation products 2

No.:

#2

Reference

Reference substance name:

Unnamed

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

- Pathways for transformation: Cleavage of the sulfonylurea bridge is the predominant hydrolysis reaction of the test substance. The two major primary radiolabeled products are IN-D7556, formed from [triazine(U) label-14C] test substance, and IN-D5803, resulting from [phenyl(U) label-14C] test substance. IN-D5803 further hydrolyses to IN-00581. IN-D5119 was also observed at pH 4 and high temperature (50°C). A secondary or minor mode of hydrolysis is via demethylation of a triazine methoxy group to form IN-N7468 (N-demethyl test substance).

Total recovery of test substance (in %)

Total recovery of test substance (in %) 1

% Recovery:

98.1

pH:

4

Temp.:

10 °C

Duration:

30 d

Total recovery of test substance (in %) 2

% Recovery:

99.7

pH:

4

Temp.:

25 °C

Duration:

30 d

Total recovery of test substance (in %) 3

% Recovery:

101.5

pH:

4

Temp.:

35 °C

Duration:

30 d

Total recovery of test substance (in %) 4

% Recovery:

102

pH:

4

Temp.:

50 °C

Duration:

30 d

Total recovery of test substance (in %) 5

% Recovery:

100.4

pH:

7

Temp.:

50 °C

Duration:

30 d

Total recovery of test substance (in %) 6

% Recovery:

100.4

pH:

7

Temp.:

60 °C

Duration:

30 d

Total recovery of test substance (in %) 7

% Recovery:

102

pH:

7

Temp.:

70 °C

Duration:

30 d

Total recovery of test substance (in %) 8

% Recovery:

100.6

pH:

9

Temp.:

50 °C

Duration:

30 d

Total recovery of test substance (in %) 9

% Recovery:

102.3

pH:

9

Temp.:

60 °C

Duration:

30 d

Total recovery of test substance (in %) 10

% Recovery:

101.8

pH:

9

Temp.:

70 °C

Duration:

30 d

Dissipation DT50 of parent compound

Dissipation DT50 of parent compound 1

Key result

pH:

4

Temp.:

10 °C

Hydrolysis rate constant:

0.005 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 143.6 days

Dissipation DT50 of parent compound 2

Key result

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0.062 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 11.2 days

Dissipation DT50 of parent compound 3

Key result

pH:

4

Temp.:

35 °C

Hydrolysis rate constant:

0.198 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 3.5 days

Dissipation DT50 of parent compound 4

Key result

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

1.835 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 0.4 days

Dissipation DT50 of parent compound 5

Key result

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.071 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 9.7 days

Dissipation DT50 of parent compound 6

Key result

pH:

7

Temp.:

60 °C

Hydrolysis rate constant:

0.273 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 2.5 days

Dissipation DT50 of parent compound 7

Key result

pH:

7

Temp.:

70 °C

Hydrolysis rate constant:

2.187 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 0.3 days

Dissipation DT50 of parent compound 8

Key result

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.048 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 14.4 days

Dissipation DT50 of parent compound 9

Key result

pH:

9

Temp.:

60 °C

Hydrolysis rate constant:

0.253 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 2.7 days

Dissipation DT50 of parent compound 10

Key result

pH:

9

Temp.:

70 °C

Hydrolysis rate constant:

1.769 d-1

Type:

other: single first-order

Remarks on result:

other: DT50: 0.4 days

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

MAJOR TRANSFORMATION PRODUCTS: Refer table under Any other information on results incl. tables

Any other information on results incl. tables

A summary of the amount of the test substance and its hydrolysis products, and maximum amount reached is presented in the table:

PRODUCT	MAXIMUM %AR OBSERVED IN VARIOUS BUFFERS, (EITHER LABEL)
	PH 4 (10°C)	PH 4 (25°C)	PH 4 (35°C)	PH 4 (50°C)	PH 7 (50°C)	PH 7 (60°C)	PH 7 (70°C)	PH 9 (50°C)	PH 9 (60°C)	PH 9 (70°C)
Test substance	98.82 (Day 0)	99.29 (Day 0)	97.98 (Day 0)	100 (Day 0)	100 (Day 0)	100 (Day 0)	100 (Day 0)	100 (Day 0)	100 (Day 0)	100 (Day 0)
IN-D7556	12.07 (Day 21)	84.43 (Day 30)	72.0 (Day 30)	97.74 (Day 5)	27.75 (Day 5)	100 (Day 14)	100 (Day 4)	13.91 (Day 5)	92.44 (Day 14)	100 (Day 7)
IN-00581	14.78 (Day 30)	85.38 (Day 30)	67.76 (Day 30)	92.61 (Day 2)	<LOD	100 (Day 14)	100 (Day 4 & 7)	<LOD	95.76 (Day 14)	100 (Day 3 & 7)
IN-D5803	<LOD	<LOD	<LOD	<LOD	24.85 (Day 5)	5.10 (Day 3)	<LOD	24.33 (Day 5)	10.84 (Day 4)	<LOD
IN-D5119	<LOD	<LOD	<LOD	12.09 (Day 5)	3.91 (Day 1)	<LOD	<LOD	8.18 (Day 2)	<LOD	<LOD
IN-N7468	-	-	-	-	<LOD	<LOD	<LOD	<LOD	7.64 (Day 10)	8.82 (Day 1)

LOD = 0.4% AR

Radioactivity was quantitatively recovered from each test solution. The mass balance is summarized in the following Table: 

pH	INCUBATION TEMPERATURE (°C)	MASS BALANCE (% DOSE) AVERAGE	MASS BALANCE (% DOSE) RANGE
4	10	98.1	95.9-100.3
	25	99.7	98.8-100.4
	35	101.5	100.4-102.5
	50	102.0	101.3-103.3
7	50	100.4	99.8-100.9
	60	100.4	99.7-101.4
	70	102.0	98.7-105.7
9	50	100.6	100.1-101.1
	60	102.3	100.0-106.7
	70	101.8	100.3-105.0

The kinetic results are summarized in the following table:

TEMPERATURE (°C)			RATE CONSTANT,K(DAYS –1)	DT50 (DAYS)		DT90 (DAYS)		R²
4	10	0.0048			143.6	477	0.893
	25		0.062		11.2	37.1	0.992
	35		0.198		3.5	11.7	0.996
	50		1.835		0.4	1.3	0.998
7	50	0.071			9.7	32.2	0.975
	60		0.273		2.5	8.4	0.995
	70		2.187		0.3	1.1	0.995
9	50	0.048			14.4	48	0.893
	60		0.253		2.7	9.1	0.970
	70		1.769		0.4	1.3	0.978

Applicant's summary and conclusion

Conclusions:

This study demonstrated that the test substance was hydrolytically unstable at acidic pH conditions (pH 4), and stable at pH 7, and at pH 9. Hydrolysis occurred at a more rapid rate across all pH’s tested at higher temperature. On the basis of these results, aqueous abiotic hydrolysis would be expected to contribute to the degradation of the test substance significantly only at pH 4, under conditions associated with typical use and/or exposure.

Executive summary:

The hydrolytic stability of the test substance was investigated in sterile buffer solutions at pH 4, 7, and 9 which were incubated at either 10 ± 1°C, 25 ± 1°C, 35 ± 1°C, 50 ± 1°C, 60 ± 1°C, or 70 ± 1°C up to 30 days according to the guidelines OECD 111 and U.S. EPA OPPTS 835.2120.

Two sites of label [triazine-14C]-test substance and [phenyl-14C]-test substance were tested. Solutions of each radiolabel were prepared in 0.02 M citrate buffer (pH 4), 0.02 M TRIS-maleate buffer (pH 7) and 0.02 M sodium borate buffer (pH 9) at a nominal test concentration of 0.28 µg/mL, which is not more than one-half of the solubility of the test substance in each of these buffers.

At selected time intervals, samples were analyzed directly by liquid scintillation counting (LSC), to determine the quantity of radioactivity present in each sample. Radioactivity was quantitatively recovered from each test solution.

 

Test solutions were subject to chromatographic analysis (HPLC) to investigate the nature of any hydrolysis products formed. Hydrolysis of the test substance was pH and temperature dependant. At lower pH and higher temperature, the rate of hydrolysis was significantly faster than at high pH and lower temperature. At each pH, the hydrolysis products detected that accounted for greater than 5% of applied radioactivity (AR) were identified as the IN-D7556 and IN-00581. IN-D5803 and IN-D5119 were also observed at >5% AR in pH 4 (IN-D5119 only), 7 and 9 buffers at 50°C and 60°C. The N-demethylation product, IN-N7468 (N-Demethyl test substance) was also observed at >5% AR in pH 4 buffer at 70°C and pH 9 at 60°C.

Arrhenius analysis was performed for each pH. The activation energy, Ea, was calculated as 111.5, 157.6, and 166.1 kJ/mol for pH 4, 7, and 9, respectively. The coefficient of determination, r², was 0.9974, 0.9804, and 0.9961 for pH 4, 7, and 9, respectively. The calculated average DT50 at 20°C was estimated to be 28 days for pH 4, and the test substance was stable at both, pH 7 and pH 9.

This study demonstrated that the test substance was hydrolytically unstable at acidic pH conditions (pH 4), and stable at pH 7, and at pH 9. Hydrolysis occurred at a more rapid rate across all pH’s tested at higher temperature.

On the basis of these results, aqueous abiotic hydrolysis would be expected to contribute to the degradation of the test substance significantly only at pH 4, under conditions associated with typical use and/or exposure.