imidacloprid (ISO); 1-(6-chloropyridin-3-ylmethyl)-N-nitroimidazolidin-2-ylidenamine

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

03 Sep 2013 - 31 Jan 2014

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

adopted in 2004

Deviations:

yes

Remarks:

Recoveries for later stages of the experiments, given by respective mass balances, are not provided

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: depending on pH treatment: 0 hours, 2 hours, 6 hours, day 1, 2, 4, 5, 6, 7, 8, 9, 11, 12, 14, 16, 19, 20, 21, 24, 26, 28, 31.
- Sampling method: At each timepoint, duplicate samples were removed from the constant temperature environment and stored until analysis.
- Sampling intervals/times for pH measurements: The pH of the samples was measured after the HPLC sequence was finished. pH did not significantly change during the course of the study, except for the pH9 at 20°C hydrolysis set.
- Sample storage conditions before analysis: After incubation the samples were transferred into a freezer to prevent a possible further hydrolysis. When the last sampling interval was finished, the samples were thawed, homogenized and subsequently placed in the auto sampler of the HPLC for analysis.

Buffers:

- pH: 4, 7 and 9
- Composition of buffer:
pH 4: 410 mL of stock solution A (5.997 g of acetic acid made up to 1000 mL with destilled water) and 90 mL of stock solution B (27.215 g sodium acetate trihydrate [CH3COONa * 3 H2O] were made up to 1000 mL with destilled water) were made up to 1000 mL with destilled water;
pH 7: 306 mL of stock solution B (11.878 g disodium hydrogen phosphate - dihydrate [Na2HPO4 * 2 H2O] were made up to 1000 mL with destilled water) were made up to 500 mL with stock solution A (9.075 g of potassium dihydrogen phosphate [KH2PO4] were made up to 1000 mL with destilled water);
pH 9: 150 mL of stock solution B (0.1 M hydrochlorid acid) were made up to 1000 mL with stock solution A (19.068 g borax [Na2B4O7 * 10 H2O] were made up to 1000 mL with destilled water).

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: incubation in HPLC vials
- Sterilisation method: All buffer solutions were completely filtered over a presterilized 0.22 µm "Satorius stedim, Sartolab 180C3 Disposable vacuum Filter Unit" with connected sterilized stock bottle.
- Cleaning and sterilization of used glassware: All glassware and materials which were in contact with the measuring solutions were cleaned thoroughly in a laboratory cleaning machine at 80 °C. Then the equipment was stored in a drying oven at 180 °C for at minimum 4 hours, before they were used. Thermally sensitive material like caps for HPLC vials were sterilized in pure ethanol for 2 hours.
- Measures to exclude oxygen: incubation vials were closed
- If no traps were used, is the test system closed/open: closed

TEST MEDIUM
- Kind and purity of water: Double destilled water, Roth, 3478
- Preparation of test medium: 1.0 mL of test substance solution (4.868 g/L) was added to 99 mL of the respective buffer solution

OTHER TEST CONDITIONS
- Incubation temperature: 50.0 °C

Duration:

144 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

49.17 mg/L

Duration:

144 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

49.27 mg/L

Duration:

479 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

49.2 mg/L

Duration:

747 h

pH:

9

Temp.:

20 °C

Initial conc. measured:

48.67 mg/L

Duration:

266.5 h

pH:

9

Temp.:

60 °C

Initial conc. measured:

52.33 mg/L

Number of replicates:

2

Positive controls:

no

Negative controls:

yes

Remarks:

Hydrolysis after 0 hours

Preliminary study:

In the preliminary test (Tier 1) at 50°C the test item was stable at pH 4 and pH 7 due to the fact that the observed hydrolysis was less than 10% after five days (120 h) at the test temperature of 50°C
± 5°C. Therefore no further testing was necessary at pH 4 and pH 7. According to the guideline a half-life time at 25°C of more than one year may be estimated at pH 4 and pH 7.

Transformation products:

not specified

Remarks:

Two hydrolysis products were found with monoisotopic masses of 273.07 Da and 211.04 Da

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

- Formation and decline of each transformation product during test: The test substance did not degrade at pH 4 and 7. In the pH 9 solution two degradation products were detected and not further identified. The diagrams show that degradation product 1 is only an intermediate species which itself undergoes abiotic degradation. Under basic conditions the graphical plot of Ln [%Imidacloprid] against time was in all cases a straight line with a correlation coefficient of 0.937 or greater. This demonstrated that at pH 9 first order kinetics was in operation at all temperatures studied.

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

Type:

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

Remarks on result:

hydrolytically stable based on preliminary test

Remarks:

Preliminary test (Tier 1): Hydrolysis < 10% after 120 hours at 50 °C

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Type:

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

Remarks on result:

hydrolytically stable based on preliminary test

Remarks:

Preliminary test (Tier 1): Hydrolysis < 10% after 120 hours at 50 °C

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.003 d-1

DT50:

240.5 d

Type:

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

Remarks on result:

not measured/tested

Remarks:

calculated based on the result of a tested temperature of 50 °C

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0.001 d-1

DT50:

515.33 d

Type:

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

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.091 d-1

DT50:

7.59 d

Type:

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

Remarks on result:

other:

Remarks:

Preliminary test (Tier 1)

pH:

9

Temp.:

60 °C

Hydrolysis rate constant:

0.307 d-1

DT50:

2.25 d

Type:

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

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): In Tier 2 test set at pH 9 and 20°C, pH was not constant throughout the experiment.

PATHWAYS OF HYDROLYSIS
- Figures of chemical structures attached: Yes

At pH 9 hydrolysis of the test item was observed at 50°C. Therefore further tests (Tier 2 and Tier 3) were performed. The hydrolysis rate constants were determined at 60°C, 50°C and 20°C. From these results hydrolysis rate constant and half-life time at 25°C was interpolated.

Validity criteria fulfilled:

not applicable

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

Version / remarks:

1982

GLP compliance:

yes

Radiolabelling:

yes

Transformation products:

yes

Remarks:

Two hydrolysis products were found, but the exact chemical structures could not be elucidated

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.002 d-1

DT50:

355 d

Type:

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

pH:

7

Temp.:

25 °C

Remarks on result:

hydrolytically stable based on preliminary test

pH:

5

Temp.:

25 °C

Remarks on result:

hydrolytically stable based on preliminary test

Validity criteria fulfilled:

not applicable

Conclusions:

NTN 33893 was very stable in the buffer adjusted to pH 5 and pH 7 in the dark at 25°C. No hydrolysis product was observed at any sampling intervals for maximum of 30 days under the conditions. NTN 33893 degraded slightly in the buffer adjusted to pH 9 and two hydrolysis products were found. These products were accounted for less than 10 % of the radioactivity (maximum 5.3 %) during the study. The experimental half-life of NTN 33893 in pH 9 was calculated to be 355 days (Rate constant K = 1.95E-03/day).

Description of key information

(2E)-1-[(6-chloropyridin-3-yl)methyl]-N-nitroimidazolidin-2-imine is not hydrolytically degraded at pH 4 or 7 (DT50 > 1 year). At pH 9 and 25 °C the degradation half-life of the substance is 240.5 d.

Key value for chemical safety assessment

Half-life for hydrolysis:

240.5 d

at the temperature of:

25 °C

Additional information

Two GLP guideline studies on the hydrolytic degradation of the substance are available.

The first study was performed according to OECD Guideline 111 (Hydrolysis as a Function of pH) and revealed a half-life of 240.5 days at pH 9 and 25 °C. At pH 4 and 7 at a temperature of 25 °C, the DT50 was estimated to be >1 year.

This result is supported by a study performed according to EPA Guideline Subdivision N 161-1 (Hydrolysis). A half-life of 355 days was determined at pH 9 and 25 °C. At pH 5 and 7 at a temperature of 25 °C, the DT50 was estimated to be >1 year.