clothianidin (ISO); (E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25 Jun 1998 - 05 Jun 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

Version / remarks:

1982

Qualifier:

according to guideline

Guideline:

other: EC Directive 94/37/EC, Active Substances, Section 2.9.1

Version / remarks:

1994

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Details on sampling:

- The hydrolysis of the test substance (CAS name N-[(2-chloro-5-thiazolyl)methyl]-N'-methyl-N"-nitroguanidine) has been studied in sterile aqueous solution at pH 4, 7 and 9 to meet the requirements of the EC Directive 94/37/EC, Active Substances, Section 2.9.1 (July 1994) and EEC method C.7. The preliminary study was performed at 50 °C and this triggered a definitive study at pH 9 only. Two additional temperatures (62 °C and 74 °C) were used and the results were used to determine the degradation rate at pH 9 and 20°C using the Arrhenius equation. The hydrolysis rate was also studied at pH 5, 7 and 9 at a temperature of 25°C to meet the requirements of the EPA Pesticide Assessment Guideline, Subdivision N, Section 161-1 (October 1982). All experiments were performed in the dark.

- For the preliminary study (50°C), duplicate vials were analysed at 0, 0.1, 1 and 5 days after test article application at pH 4, 7 and 9 and additionally after 11, 15, 19 and 25 days at pH 9. For the definitive study (25 °C), duplicate vials at all pH values were analysed at 0, 5, 9, 15, 20, 27 and 33 days after test article application. For the additional definitive studies (pH 9 only) duplicate vials were analysed at 0, 1, 3 and 7 days (62 °C) and 0, 0.25, 1 and 1.9 days (74°C). At each sampling time, buffer solutions dosed with radiolabelled test article were removed from the incubation system and cooled rapidly by placing them in cold water. Radioactivity contained in each vial was determined by removing weighed aliquots (50 µL) for LSC. A portion of each sample (ca 1 mL) was transferred into a separate vial for HPLC analysis (Method 2). Aliquots of the buffer solution from samples incubated at 25 °C, 62 °C and 74 °C were also analysed by TLC. Duplicate non-dosed samples were analysed for pH and sterility prior to the start of each phase of the study. At the end of each phase of the study, vials dosed with non-radiolabelled test article were removed from the incubation system for pH and sterility testing.

Buffers:

PREPERATION OF BUFFER SOLUTIONS
- pH 4: A 0.01M potassium hydrogen phthalate buffer (pH 4) was prepared by adding 0.01M sodium hydroxide solution to 0.01M potassium hydrogen phthalate solution until the pH of the solution was 4.0 at 50 °C.
- pH 5: A 0.01M sodium citrate buffer (pH 5) was prepared by adding 0.01M trisodium citrate solution to 0.01M citric acid solution until the pH of the solution was 5.0 at 25 °C.
- pH 7: 0.01M TRIS maleic acid buffer solutions were prepared by adding 0.01M sodium hydroxide solution to 0.01M TRIS-maleic acid solution until the pH values of the solutions were 7.0 at the temperatures of the proposed incubations (25 °C or 50 °C).
- pH 9: 0.01M Borate-boric acid buffer solutions were prepared by adjusting the pH of 0.0025M sodium tetraborate solutions with 0.01M sodium hydroxide solution or 0.01M boric acid solution until the pH values of the solutions were 9.0 at the temperatures of the proposed incubations (25 °C, 50 °C, 62 °C or 74 °C).

Details on test conditions:

- All solutions were prepared in 'HiPerSolv' HPLC grade water. Portions (3 mL) of the prepared buffers were dispensed into borosilicate glass vials (capacity 4 mL, type 4-CV from Chromacol, Welwyn Garden City, Hertfordshire), which were then sealed, with crimped PTFE-lined rubber caps. Sealed vials were labelled with a unique sample code and were sterilised by autoclaving. The pH and sterility of the buffer solutions were checked after sterilisation using two control vials per pH value.

- All experiments were performed in the dark.

- In order to check for adsorption of the test substance to the walls of the test apparatus duplicate aliquots were taken for determination of radioactivity by liquid scintillation counting (LSC) immediately after dosing, after 1 hour and after 3 days. Mean recovery of applied radioactivity was >97% at all times demonstrating insignificant adsorption to glass.

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Preliminary study (Tier 1)

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Preliminary study (Tier 1)

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Preliminary study (Tier 1)

Duration:

25 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Preliminary study (Tier 1)

Duration:

33 d

pH:

4

Temp.:

25 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Definitive study (Tier 2 & 3)

Duration:

33 d

pH:

7

Temp.:

25 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Definitive study (Tier 2 & 3)

Duration:

33 d

pH:

9

Temp.:

25 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Definitive study (Tier 2 & 3)

Duration:

7 d

pH:

9

Temp.:

62 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Definitive study (Tier 2 & 3)

Duration:

1.9 d

pH:

9

Temp.:

74 °C

Initial conc. measured:

0.3 mg/L

Remarks:

Definitive study (Tier 2 & 3)

Number of replicates:

At each sampling time duplicate samples were sacrificed for analysis.

Positive controls:

no

Negative controls:

yes

Remarks:

Duplicate non-dosed samples were analysed for pH and sterility prior to the start of each phase of the study.

Preliminary study:

The preliminary study was performed at 50 °C and this triggered a definitive study at pH 9 only.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

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

- Formation and decline of each transformation product during test:
At 50 °C, no degradation products could be detected after 5 days at pH 4 or 7 but 2-chlorothiazol-5-ylmethylamine (ACT), N-(2-chlorothiazol-5-ylmethyl)-N'-nitrourea (CTNU) and N-(2-chlorothiazol-5-ylmethyl)-N'-methylurea (TZMU) were observed at pH 9. The test substance decreased from 100%, initially, to 29% over the 25 day incubation period. Levels of CTNU increased to 8% of applied radioactivity after 5 days and thereafter decreased slowly to 4% at 25 days. Levels of TZMU and ACT increased steadily to 11% and 53% respectively. No other degradation products were detected. The identities of the degradates were confirmed by TLC of samples from 62 °C and 74 °C studies.
At 62 °C, CTNU increased to 5% of applied radioactivity after 1 day and thereafter decreased to 2% after 7 days. TZMU and ACT increased to 15% and 54% respectively and the test substance decreased from 100%, initially, to 27% over the 7 day incubation period.
At 74 °C, CTNU increased to 5% of applied radioactivity after 6 hours thereafter decreased to 1% after 1.9 days. TZMU and ACT increased to 23% and 59% respectively and the test substance decreased from 100%, initially, to 14% over the 1.9 day incubation period.
- Other: Degradation products CTNU, TZMU and ACT were detected by HPLC and confirmed by TLC. No other significant degradation products were observed.

pH:

4

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other:

Remarks:

% Recoervy: 96 - 102

pH:

7

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other:

Remarks:

% Recoervy: 96 - 102

pH:

9

Temp.:

50 °C

Duration:

25 d

Remarks on result:

other:

Remarks:

% Recoervy: 96 - 102

pH:

5

Temp.:

25 °C

Duration:

33 d

Remarks on result:

other:

Remarks:

% Recoervy: 97 - 103

pH:

7

Temp.:

25 °C

Duration:

33 d

Remarks on result:

other:

Remarks:

% Recoervy: 97 - 103

pH:

9

Temp.:

25 °C

Duration:

33 d

Remarks on result:

other:

Remarks:

% Recoervy: 97 - 103

% Recovery:

> 96 - < 100

pH:

9

Temp.:

62 °C

Duration:

7 d

% Recovery:

> 96 - < 100

pH:

9

Temp.:

74 °C

Duration:

1.9 d

pH:

4

Temp.:

50 °C

DT50:

> 1 yr

Type:

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

pH:

7

Temp.:

50 °C

DT50:

> 1 yr

Type:

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

pH:

5

Temp.:

25 °C

DT50:

> 1 yr

Type:

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

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Type:

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

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.048 d-1

DT50:

14.4 d

Type:

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

pH:

9

Temp.:

62 °C

Hydrolysis rate constant:

0.188 d-1

DT50:

3.7 d

Type:

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

pH:

9

Temp.:

74 °C

Hydrolysis rate constant:

1.013 d-1

DT50:

0.68 d

Type:

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

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0 d-1

DT50:

1 401 d

Type:

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

Remarks on result:

not measured/tested

Remarks:

calculated based on the result of a tested temperatures of 50, 62 and 74 °C

pH:

9

Temp.:

12 °C

DT50:

2 974.3 d

Type:

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

Remarks on result:

not measured/tested

Remarks:

recalculated based on the calculated DT50 at 20 °C

Details on results:

EPA Guideline hydrolysis study at 25 °C:

- The test was performed for 33 days at pH values of 5, 7 and 9. Total recovery of applied radioactivity was in the range 97 to 103% at each timepoint.
- No degradation of test article after 33 days at pH 5 or 7 and at 25 °C was observed by HPLC but at pH 9 a small degree of degradation occurred. TLC confirmed that no significant degradation had occurred after 33 days at pH 5 or 7 and confirmed the presence of low levels of CTNU and TZMU at pH9.
- Analysis of sterility controls indicated microbial contamination of some of the vials, however, no significant degradation of the test substance occurred at pH 5 or 7 therefore the conclusion that the compound is hydrolytically stable at these pH values is valid. Two 20-day study samples were analysed for sterility and were shown to be sterile. The small degree of degradation (ca 4% over 33 days) at pH 9 was almost certainly hydrolytic rather than microbial. Studies performed at pH 9 and different temperatures for EC registration (see below) show degradation at pH 9 under sterile conditions at higher temperatures.


EC Guideline hydrolysis study Hydrolysis at 50 °C:

- The test was performed for 5 days (pH 4 and 7) or 25 days (pH 9). Total recovery of applied radioactivity was in the range of 96 to 102% at each timepoint. The sterility controls were shown to be sterile.
- Less than 10% of the test substance hydrolysed after 5 days at pH 4 and 7. EEC method C.7 states that the value of 10% hydrolysis after 5 days at 50°C corresponds to a half-life greater than one year at conditions representative of the environment (25 °C). If degradation is slower than this, the guideline does not require further temperatures to be studied.
- No degradation products could be detected after 5 days at pH 4 or 7 but ACT, CTNU and TZMU were observed at pH 9. The test substance decreased from 100%, initially, to 29% over the 25 day incubation period. Levels of CTNU increased to 8% of applied radioactivity after 5 days and thereafter decreased slowly to 4% at 25 days. Levels of TZMU and ACT increased steadily to 11% and 53% respectively. No other degradation products were detected. The identities of the degradates were confirmed by TLC of samples from 62 °C and 74 °C studies.


Further tests at pH 9:

- The hydrolysis at pH 9 was studied at two temperatures above 50 °C differing from each other by at least 10 °C (temperatures of 62 °C and 74 °C were used) so that accurate rate constants could be determined. The tests were performed until two timepoints had been obtained after 30% hydrolysis as prescribed by EEC method C.7. The 62 °C study was terminated after 7 days and the 74 °C study after 1.9 days. Total recovery of applied radioactivity was in the range 96 to 100% at each timepoint.
- At 62 °C, CTNU increased to 5% of applied radioactivity after 1 day and thereafter decreased to 2% after 7 days. TZMU and ACT increased to 15% and 54% respectively and the test substance decreased from 100%, initially, to 27% over the 7 day incubation period. At 74 °C, CTNU increased to 5% of applied radioactivity after 6 hours thereafter decreased to 1% after 1.9 days. TZMU and ACT increased to 23% and 59% respectively and the test substance decreased from 100%, initially, to 14% over the 1.9 day incubation period.

Validity criteria fulfilled:

not applicable

Conclusions:

The hydrolysis of the test substance has been studied over a range of pH values and temperatures. The compound was shown to be stable at pH 4, 5 and 7 but slowly degraded at pH 9. By using different temperatures (50 °C, 62 °C and 74 °C), it was possible to show that the half-life of the test substance at pH 9 and 20 °C would be ca 3.8 years. The degradation rate at pH 9 and 25 °C was too slow to be determined but chromatography showed that a small degree of degradation occurred within the 33 day incubation period.
Three products were formed by hydrolysis at pH 9 at elevated temperatures. One product, identified as ACT, increased steadily throughout the incubation periods. No later products were formed and it was therefore clearly an end product. Another product, identified as CTNTJ, reached an early maximum concentration and then decreased. It was therefore an intermediate. The final product, identified as TZMU, increased throughout the incubation period but its rate of increase slowed with time. Based upon this, and also its structure, this compound was also most likely to be an intermediate. The products were identified by co-chromatography with authentic standards in two chromatographic systems.

Description of key information

(E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine is not hydrolytically degraded at pH 4, 5 or 7. At pH 9 and 20 °C the degradation half-life of the substance is ca. 3.8 years.

Key value for chemical safety assessment

Half-life for hydrolysis:

3.8 yr

at the temperature of:

20 °C

Additional information

The compound (E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine was shown to be stable at 50 °C and pH 4, 5 and 7 but slowly degraded at pH 9. By using different temperatures (50°C, 62°C and 74°C), it was possible to show that the half-life of the test substance at pH 9 and 20°C would be ca 3.8 years.

Although transformation products were produced at pH 9 from the test substance, they were only produced at artificially high temperatures. At the temperature of environmental concern (20°C), the test substance has a half-life of ca 3.8 years and therefore these products would not be expected to be produced in significant amounts. No hydrolysis of the test substance would be expected to occur under neutral or acidic conditions.