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Environmental fate & pathways

Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key 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 (incl. QA statement)
Radiolabelling:
yes
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the parent/transformation products: The test solutions were sampled at the following times after the treatment:
pH 5: 0,1, 3, 7, 14. 21 and 30 days
pH 7: 0.1. 3. 7, 14. 21 and 30 days
pH 9: 0, 1. 3, 7. 14, 21. 30. 60 and 120 hr.
- Sampling method: Five test vessels were sampled at each of the above mentioned times after the dosing.
- Sampling intervals/times for pH measurements: At each of the above mentioned sampling times the pH of the test solution was measured.
- Sampling intervals/times for sterility check: At each of the above mentioned sampling times the sterility of the test solution was measured.
- Sampling intervals/times for temperature: The temperature (°C) was recorded every 10 min (on a real time basis) using a data acquisition and process control software (Control EG; Quinn-Curtis, Newton, MA). To cover possible computer interruptions, the temperature was also recorded manually at least once a day.
- Sample storage conditions before analysis: All analyses and measurements were performed immediately after sampling.
Buffers:
- pH: 5, 7 and 9.
- Type and final molarity of buffer: Final molarity was 0.01 M. Sterile deionized water (Millipore Killi-Q System) was used for the preparation of the buffers. Just before dosing, the buffers were sterilized once again by passing through a membrane filter assembly (0.2 micrometer; Acrodisc No. 4192; Gel man Sciences, Ann Arbor, MI).
- Composition of buffer:
pH 5: Glacial acetic acid (CH3COOH) (FW 60.05; Sp. Gr. 1.05), 57.5 mL, was dissolved in sterile deionized water to a final volume of 1000 mL in a volumetric flask. An aliquot of 10 mL of this solution was further diluted to 1000 mL with sterile deionized water in a volumetric flask. The pH was checked and adjusted to pH 5.0 with 0.1 N sodium hydroxide solution.
pH 7: Potassium phosphate, monobasic (anhydrous. >99% pure. Mol . Wt. 136.1; Lot No. 31F0105, Sigma Chem. Co., St. Louis, MO), 2.722 g, was dissolved in 1000 mL (final volume) of sterile deionized water, to yield 0.02 M solution. Potassium phosphate, dibasic (K2HP04) (anhydrous, analyzed reagent, Lot No. 33, J. T. Baker, Phil lipsburg, NJ), 3.484 g, was dissolved in 1000 mL (final volume) of sterile deionized water, to yield 0.02 M solution. An aliquot of 195.0 mL potassium phosphate monobasic 0.02 M solution was mixed with 305.0 mL of potassium phosphate dibasic 0.02 M solution and made up to approximately 980 mL. The pH was adjusted to 7.00 with 0.1 N hydrochloric acid. The final volume was made to 1000 mL in a volumetric flask with sterile deionized water. The pH was rechecked and adjusted to 7.00.
pH 9: Sodium borate (Na2B^07-10 H£0) (Certified ACS, FW 381.37. Lot No. 731042. Fisher Scientific Co.. Fairlawn, NJ), 19.0685 g, was dissolved in 500 mL (final volume) of sterile deionized water, to yield 0.1 M solution. An aliquot of 100 mL of this solution was diluted to approximately 980 mL with sterile deionized water and the pH was adjusted to 9.00 with 0.1 N hydrochloric acid. The final volume was made to 1000 mL in a volumetric flask with sterile deionized water. The pH was rechecked and adjusted to 9.00.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: Each test vessel consisted of a 3 mL capacity Teflon vial provided with a Teflon-stainless steel access tube.
- Sterilisation method: Prior to the introduction of the buffer solutions, the test vessels were sterilized twice by rinsing with 80% methanol and allowing to dry overnight in an incubator at ca. 35 °C.
- Measures taken to avoid photolytic effects: After dosing, the test vessels were closed air-tight and the Teflon access tubes were sealed using a pair of hot metal pliers.

TEST MEDIUM
- Volume used/treatment: 1 mL
- Preparation of test medium: Into each test vessel, 1 mL of the appropriate buffer was aseptically introduced using a sterile syringe and needle equipped with a membrane filter assembly (0.2 micrometer; Acrodisc No. 4192; Gelman Sciences, Ann Arbor, MI). The dosing solution of [phenyl (U)-14C]-bromoxynil octanoate (99,900 dpm = 1 µg) was prepared in acetone (Lot No. 870252; Fisher Scientific, Fair Lawn, NJ), and an aliquot of 5 µL of this solution (containing 1.1 µg) was added to each test vessel containing 1 mL of buffer. The applied dose of the test substance was 1.1 ppm in the final test solutions.
- Identity and concentration of co-solvent: The carrier solvent (acetone) represented 0.5% (v/v) in the final test solution.
Transformation products:
yes
No.:
#1
No.:
#2
pH:
5
Temp.:
25 °C
Duration:
30 d
Remarks on result:
other:
Remarks:
% Recovery of applied radioactivity after 30 days: 100.6
% Recovery:
100
pH:
7
Temp.:
25 °C
Duration:
30 d
Remarks on result:
other:
Remarks:
% Recovery of applied radioactivity after 30 days: 100.0
% Recovery:
94.8
pH:
9
Temp.:
25 °C
Duration:
120 h
Remarks on result:
other:
Remarks:
% Recovery of applied radioactivity after 120 hours: 94.8
pH:
9
Temp.:
25 °C
DT50:
1.7 d
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
12 °C
DT50:
5.7 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
pH:
7
Temp.:
25 °C
DT50:
11.5 d
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
12 °C
DT50:
38.5 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
pH:
5
Temp.:
25 °C
DT50:
34.1 d
Type:
(pseudo-)first order (= half-life)
pH:
5
Temp.:
12 °C
DT50:
113.5 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes. The test solutions were found to be devoid of any microbial contamination and remained sterile throughout the study, as revealed by the microscopic examination of the test solutions at the beginning and at the end of the study. The test solutions buffered at 0.01 M were found to have adequate buffering capacity, as revealed by the pH measurements of the test solutions at various sampling events.
- Other: Material balance was 98.5 ± 4.0% for pH 5, 99.5 ± 3.7% for pH 7 and 96.3 ± 2.9% for pH 9.

MAJOR TRANSFORMATION PRODUCTS
At pH5:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Under pH 5 conditions, the parent concentrations dropped from an initial 97.4% to a final 50.7% by the end of 30 days. There was a corresponding increase in the formation of bromoxynil phenol, reaching a maximum mean value of 35.0% by the end of 30 days. There was another degradate, identified as 3,5-dibromo-dihydroxy-cyclohexadienylnitrile, that reached a maximum mean concentration of 10.4% at 21 days.

At pH7:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Under pH 7 conditions, the parent concentrations dropped from an initial 95.8% to a final 14.8% by the end of 30 days. There was a corresponding increase in the formation of bromoxynil phenol, reaching a maximum mean value of 77.2% by the end of 30 days. There was another degradate, identified as 3,5-dibromo-dihydroxy-cyclohexadienylnitrile, that reached a maximum mean concentration of 10.7% at 21 days.

At pH9:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Under pH 9 conditions, the parent concentrations dropped rapidly from an initial 96.2% to a final 12.7% by the end of 120 hr. There was a corresponding increase in the formation of bromoxynil phenol, reaching a maximum mean value of 76.0% by the end of 120 hr. There was another degradate. identified as 3,5-dibromo-dihydroxy-cyclohexadienylnitrile, that reached a maximum mean concentration of 7.9% at 30 hr.

PATHWAYS OF HYDROLYSIS
- Description of pathways: The nature of degradation products under pH 5, 7 and 9 were identical, but quantitatively different in a pH-dependent pattern. The susceptibility of bromoxynil octanoate to hydrolysis increased with the pH value. Based on the quantitative yield of the ring-labeled degradates, it appears reasonable to conclude that bromoxynil octanoate -- being an ester -- is hydrolytically broken into the respective acidic and alcoholic moieties. Furthermore, the latter group was found to undergo hydroxylation, resulting in a more polar dihydroxy derivative.
- Figures of chemical structures attached: Yes
Validity criteria fulfilled:
not applicable
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:
other: U.S. Environmental Protection Agency Pesticide Assessment Guidelines, Subdivision N: Environmental Fate, Section 161-lc2ii, October 18, 1982.
Version / remarks:
1982
GLP compliance:
no
Radiolabelling:
yes
Duration:
31 d
pH:
9
Temp.:
23 °C
Initial conc. measured:
9.6 other: ppb
Duration:
31 d
pH:
7
Temp.:
23 °C
Initial conc. measured:
9.6 other: ppb
Duration:
31 d
pH:
5
Temp.:
23 °C
Initial conc. measured:
9.6 other: ppb
Transformation products:
yes
Remarks:
The principal degradation product of both the octanoate and butyrate was the 2,6-dibromo-4-cyanophenol. The minor degradation products detected by thin layer chromatographic analysis corresponded to less than 5% of the initial radiocarbon.
pH:
9
Temp.:
23 °C
Hydrolysis rate constant:
0.019 h-1
DT50:
36 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
12 °C
DT50:
8.4 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
pH:
7
Temp.:
23 °C
Hydrolysis rate constant:
0.025 d-1
DT50:
28 d
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
12 °C
DT50:
78 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
pH:
5
Temp.:
23 °C
Hydrolysis rate constant:
0.016 d-1
DT50:
43 d
Type:
(pseudo-)first order (= half-life)
pH:
5
Temp.:
12 °C
DT50:
120 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
Validity criteria fulfilled:
not applicable
Conclusions:
The rates of hydrolysis of 14C-ring-labeled bromoxynil octanoate (2,6-dibromo-4-cyanophenyl octanoate) and bromoxynil butyrate (2,3-dibromo-4-cyanophenyl butyrate) were determined in aqueous buffered solutions adjusted to pH 5, 7, and 9. Sufficient radiolabeled material was added to the sterilized solution to obtain a concentration of 2.5 ppm bromoxynil butyrate in pH 5, 7, and 9, solutions and concentrations of 9.6 ppb bromoxynil octanoate in pH 5 and 7 solutions and 15.7 ppb in pH 9 solution. The preparations were incubated in the dark at room temperature, 23°C, for periods up to 31 days.
No volatile degradation products were formed during the test period. The hydrolysis of the esters to the corresponding phenol (2,6-dibromo-4-cyano phenol) was rapid at pH 9 with half-lives, t-1/2, of 26 hours for the butyrate and 36 hours for the octanoate. The degradation at pH 5 and 7 was slower for both compounds: butyrate, pH 5, t-1/2 44 day, pH7, t-1/2 52 days; octanoate pH5, t-1/2 43 days, pH 7, t-1/2 28 days.
The principal degradation product of both the octanoate and butyrate was the 2,6-dibromo-4-cyanophenol. The minor degradation products detected by thin layer chromatographic analysis corresponded to less than 5% of the initial radiocarbon. The analysis of pH 9 samples taken at 30 days indicated that the phenol was stable over an extended period of time.
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:
no
Radiolabelling:
yes
Duration:
30 d
pH:
9
Temp.:
25 °C
Initial conc. measured:
0.064 other: ppm
Duration:
30 d
pH:
7
Temp.:
25 °C
Initial conc. measured:
0.072 other: ppm
Duration:
30 d
pH:
5
Temp.:
25 °C
Initial conc. measured:
0.072 other: ppm
Transformation products:
yes
Remarks:
The major degradate was bromoxynil; however there was significant formation of the amide (3,5-dibromo-4-hydroxy benzamide) through the hydrolysis of bromoxynil in the pH 7 buffer systems.
pH:
9
Temp.:
25 °C
DT50:
3.9 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.10 M.
pH:
9
Temp.:
12 °C
DT50:
13 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.10 M calculated to 12 °C.
pH:
9
Temp.:
25 °C
DT50:
4.8 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.05 M.
pH:
9
Temp.:
12 °C
DT50:
16 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.05 M calculated to 12 °C.
pH:
9
Temp.:
25 °C
DT50:
6.5 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.01 M.
pH:
9
Temp.:
12 °C
DT50:
21.6 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.01 M calculated to 12 °C.
pH:
7
Temp.:
25 °C
DT50:
5.2 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.10 M.
pH:
7
Temp.:
12 °C
DT50:
17.3 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.10 M calculated to 12 °C.
pH:
7
Temp.:
25 °C
DT50:
4.3 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.05 M.
pH:
7
Temp.:
12 °C
DT50:
14.3 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.05 M calculated to 12 °C.
pH:
7
Temp.:
25 °C
DT50:
4.3 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.01 M.
pH:
7
Temp.:
12 °C
DT50:
14.3 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.01 M calculated to 12 °C.
pH:
5
Temp.:
25 °C
DT50:
4.6 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.10 M.
pH:
5
Temp.:
12 °C
DT50:
15.3 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.10 M calculated to 12 °C.
pH:
5
Temp.:
25 °C
DT50:
5.3 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.05 M.
pH:
5
Temp.:
12 °C
DT50:
17.7 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.05 M calculated to 12 °C.
pH:
5
Temp.:
25 °C
DT50:
6.2 d
Type:
zero order
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.01 M.
pH:
5
Temp.:
12 °C
DT50:
20.6 d
Remarks on result:
other:
Remarks:
Half-life of test compound at an ionic strength of 0.01 M calculated to 12 °C.
Validity criteria fulfilled:
not applicable
Conclusions:
Radiolabelled 14-C Bromoxynil Octanoate was subjected to a 30 day hydrolysis study at three pH levels of three different ionic strengths. Bromoxynil Octanoate readily degrades in aqueous media at pH levels of 5, 7 and 9 with ionic strengths at molar concentrations of 0.01, 0.05 and 0.10. The half-life of bromoxynil octanoate, calculated by linear regression analysis, after one month of incubation under sterile conditions at 25 ± 1° C ranges from 3.9 to 6.5 days with an average of 5.0 days. The major degradate was bromoxynil; however there was significant formation of the amide (3,5-dibromo-4-hydroxy benzamide) through the hydrolysis of bromoxynil in the pH 7 buffer systems.
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:
other: U.S. Environmental Protection Agency Pesticide Assessment Guidelines, Subdivision N: Environmental Fate, Section 161-lc2ii, October 18, 1982.
Version / remarks:
1982
GLP compliance:
no
Radiolabelling:
yes
Duration:
31 d
pH:
9
Temp.:
23 °C
Initial conc. measured:
0.01 mg/L
Duration:
31 d
pH:
7
Temp.:
23 °C
Initial conc. measured:
0.01 mg/L
Duration:
31 d
pH:
5
Temp.:
23 °C
Initial conc. measured:
0.01 mg/L
Transformation products:
yes
Remarks:
The principal degradation product of the octanoate was the 2,6-dibromo-4-cyanophenol. The minor degradation products detected by thin layer chromatography analysis corresponded to less than 5% of the initial radiocarbon.
pH:
9
Temp.:
23 °C
Hydrolysis rate constant:
0.019 h-1
DT50:
36 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
12 °C
DT50:
8.4 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
pH:
7
Temp.:
23 °C
Hydrolysis rate constant:
0.025 d-1
DT50:
28 d
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
12 °C
DT50:
78 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
pH:
5
Temp.:
23 °C
Hydrolysis rate constant:
0.016 d-1
DT50:
43 d
Type:
(pseudo-)first order (= half-life)
pH:
5
Temp.:
12 °C
DT50:
120 d
Remarks on result:
other:
Remarks:
DT50 recalculated to 12 °C
Validity criteria fulfilled:
not applicable
Conclusions:
The rate of hydrolysis of 14C-ring-labeled bromoxynil octanoate (2,6-dibromo-4-cyanophenyl pctanoate) was determined in aqueous buffered solutions adjusted to pH 5, 7, and 9. Sufficient radiolabeled material was added to the sterilized solution to obtain a concentration of 9.6 ppb bromoxynil octanoate in pH 5 and 7 solutions and 15.7 ppb in pH 9 solution. The preparations were incubated in the dark at room temperature, 23 °C, for periods up to 31 days.
No volatile degradation products were formed during the test period. The hydrolysis of the ester to the corresponding phenol (2,6-dibromo-4-cyano-phenol) was rapid at pH 9 with half-life, t-1/2, of 36 hours. The degradation at pH 5 and 7 was slower pH5, t-1/2, 43 days, pH 7, t-1/2, 28 days.
The principal degradation product of the octanoate was the 2,6-dibromo-4-cyanophenol. The minor degradation products detected by thin layer chromatography analysis corresponded to less than 5% of the initial radiocarbon. The analysis of pH 9 samples taken at 30 days indicated that the phenol was stable over an extended period of time.
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
GLP compliance:
no
Radiolabelling:
yes
Duration:
14 d
pH:
9
Temp.:
25 °C
Initial conc. measured:
1 other: ppm
Duration:
14 d
pH:
7
Temp.:
25 °C
Initial conc. measured:
1 other: ppm
Duration:
14 d
pH:
5
Temp.:
25 °C
Initial conc. measured:
1 other: ppm
Transformation products:
yes
Remarks:
Bromoxynil Octanoate hydrolyzed to Bromoxynil at all three pH levels.
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.361 d-1
DT50:
1.9 d
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
12 °C
DT50:
6.3 d
Remarks on result:
other:
Remarks:
Calculated DT50 at 12 °C
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.312 d-1
DT50:
2.2 d
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
12 °C
DT50:
2.2 d
Remarks on result:
other:
Remarks:
Calculated DT50 at 12 °C
pH:
5
Temp.:
25 °C
Hydrolysis rate constant:
0.397 d-1
DT50:
1.75 d
Type:
(pseudo-)first order (= half-life)
pH:
5
Temp.:
12 °C
DT50:
5.8 d
Remarks on result:
other:
Remarks:
Calculated DT50 at 12 °C
Validity criteria fulfilled:
not applicable
Conclusions:
The hydrolysis of 14C-Bromoxynil Octanoate (1 ppm) has been studied in sterile water at 3 pH levels (5, 7, and 9). The three flasks were observed over a 14 day period in the absence of light at 25°C. About 1% of acetonitrile was added to each flask as a vehicle to solubilize the Bromoxynil Octanoate. Periodic samples from each pH flask were subjected to extraction and TLC/autoradiography for an assessment of the hydrolysis of Bromoxynil Octanoate.
Bromoxynil Octanoate hydrolyzed to Bromoxynil at all three pH levels with a calculated half life of 1.75, 2.2 and 1.9 days for the pH 5, 7, 9 flasks, respectively. Once the free phenol (Bromoxynil) was formed from the hydrolysis of the octanoate ester, it remained unchanged during thecourse of this study. By day 14 essentially complete hydrolysis of the ester linkage had occurred.

Description of key information

Half-life at 25°C: 1.7 days at pH 9, 11.5 days at pH 7 and 34.1 days at pH 5 (5.7, 38.3 and 113.5 days, recalculated to 12 °C; EPA Guideline N161-1).

Key value for chemical safety assessment

Half-life for hydrolysis:
38.3 d
at the temperature of:
12 °C

Additional information

The key study, following GLP and EPA Guideline N161-1, assessed the hydrolytic degradation of 2,6-dibromo-4-cyanophenyl octanoate at 25 °C and under alkaline (pH 9), neutral (pH 7) and acidic (pH 5) conditions. The DT50 of the test substance was 1.7 days at pH 9, 11.5 days at pH 7 and 34.1 days at pH 5 (5.7, 38.3 and 113.5 days, recalculated to 12 °C).

 

Two supporting studies, following the EPA Guideline N161-1, came to the same results with half-lives of 36 hours at pH 9, 28 days at pH 7 and 43 days at pH 5 (8.4, 78 and 120 days, recalculated to 12 °C) of 2,6-dibromo-4-cyanophenyl octanoate at 23 °C.

 

Another supporting study following the EPA Guideline N161-1 studied the hydrolytic degradation of 2,6-dibromo-4-cyanophenyl octanoate at 25 °C, under alkaline (pH 9), neutral (pH 7) and acidic (pH 5) conditions and under three different ionic strengths (0.10, 0.05 and 0.01 M). The half-life ranged from 3.9 to 6.5 days at pH 9 (13 to 21.6 days, recalculated to 12 °C), 4.3 to 5.2 at pH 7 (14.3 to 17.3 days, recalculated to 12 °C) and 4.6 to 6.2 at pH 5 (15.3 to 20.6 days, recalculated to 12 °C).

 

One more experimental study on the hydrolysis of 2,6-dibromo-4-cyanophenyl octanoate at 25 °C found half-lives of 1.9 days at pH 9, 2.2 days at pH 7 and 1.75 days at pH 5 (6.3, 7.3 and 5.8 days, recalculated to 12 °C).

 

For the sake of completeness and to mention all available data, a position paper on the hydrolysis products of bromoxynil and its esters is available. It shows that the only hydrolysis product of bromoxynil esters relevant to the environment is 3,5-dibromo-4-hydroxybenzonitrile, which itself is resistant to hydrolysis under sterile conditions.

In accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5 “Grouping of substances and read-across” and in accordance with the read across assessment framework (RAAF, ECHA 2017) a read-across from the hydrolysis of 3,5-dibromo-4-hydroxybenzonitrile has been applied to support the environmental hazard assessment of 2,6-dibromo-4-cyanophenyl heptanoate.

In the supporting study, 3,5-dibromo-4-hydroxybenzonitrile was stable at 12 °C and under alkaline (pH 9), neutral (pH 7) and acidic (pH 5) conditions with a half-life of >1 year.