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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
24 May 2013 - 14 Mar 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Version / remarks:
2004
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on source and properties of surface water:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): This study was carried out using water samples from Carsington Water. Carsington water (map ref: SK 24813 49984) is a ca. 300 hectare reservoir which stores water pumped from the river Derwent at Ambergate and also receives smaller quantities of water draining off grassland surrounding the reservoir. The river Derwent drains a mainly grassland catchment but also receives urban discharges.
- Storage conditions: Acclimated in CT-room to study temp. of 20°C overnight before flask filling (loosely lidded).
- Temperature (°C) at time of collection: 15.2
- pH at time of collection: 7.56
- Electrical conductivity: 0.16 ppt
- Oxygen concentration (mg/l) initial: 122.5
- Dissolved organic carbon (ppm): 2.7
- Water filtered: yes
- Type and size of filter used, if any: The water samples had been passed through a 100 µm sieve.
Duration of test (contact time):
60 d
Initial conc.:
10 µg/L
Based on:
test mat.
Initial conc.:
100 µg/L
Based on:
test mat.
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 100 mL/flask
- Solubilising agent (type and concentration if used): A stock solution (Stock 1) was prepared by adding 0.5 mL of ethanol:water, 95:5 v/v solvent to the vial containing [14C]-Bromoxynil Phenol.
- Test temperature: All sample, control and reference flasks (other than the zero-time samples) were incubated in the dark at 20 ± 2 °C.
- pH: 7.4 (range 6.2 to 7.9)
- Continuous darkness: yes
- Any indication of the test material adsorbing to the walls of the test apparatus: no

TEST SYSTEM
- Culturing apparatus: The test water (100 mL/flask) was added to 250 mL borosilicate glass conical flasks with ground glass joints at the neck for attachment to the aeration and volatiles trapping system.
- Number of culture flasks/concentration: For each of the two dose levels, 24 flasks containing the test water were prepared for treatment with Bromoxynil Phenol, allowing duplicate samples to be taken at each of 10 specified sampling time-points whilst leaving four flasks which could be used as spares.
- Method used to create aerobic conditions: All flasks were attached to an incubation system through which moistened air was passed, at a rate that allowed sufficient aeration of the headspace to maintain aerobic conditions and carry any volatiles formed into the trapping system.
- Details of trap for CO2 and volatile organics if used: Each flask was connected to a series of three traps, the first containing ethylene glycol and the second and third containing 2M potassium hydroxide.
- Other: Four flasks per dose level (two replicates plus two spares) were prepared as sterile controls to enable differentiation between biotic and abiotic degradation of the test item. Positive controls and solvent controls were also used during the study. Positive control flasks were treated with [Phenyl-U-14C]-benzoic acid at a nominal dose rate of 10 µg/L.

SAMPLING
- Sampling frequency: 0, 3, 7, 14, 21, 28, 35, 42, 49, 60 and 61 days after treatment each of the two dose levels duplicate flasks and their associated traps were sampled. On days 7 and 14 of the study duplicate positive control samples were also taken and on day 7 solvent controls were sampled. The sterile controls were sampled at the end of the study on day 61.
- Sampling method used per analysis type: For each of the two dose levels duplicate flasks and their associated traps were removed at each timepoint.
Compartment:
natural water: freshwater
% Total extractable:
> 100
% CO2:
0
% Recovery:
100
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 10 µg/L dose level at Day 0
Compartment:
natural water: freshwater
% Total extractable:
94.7
% CO2:
0.45
% Recovery:
95.1
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 10 µg/L dose level at Day 60
Compartment:
natural water: freshwater
% Total extractable:
> 100
% CO2:
0
% Recovery:
100
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 100 µg/L dose level at Day 0
Compartment:
natural water: freshwater
% Total extractable:
99.4
% CO2:
0.2
% Recovery:
99.6
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 100 µg/L dose level at Day 60
Parent/product:
parent
Compartment:
water
% Degr.:
0.45
Parameter:
CO2 evolution
Sampling time:
60 d
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 10 µg/L dose level after 60 days
Parent/product:
parent
Compartment:
water
% Degr.:
0.2
Parameter:
CO2 evolution
Sampling time:
60 d
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 100 µg/L dose level after 60 days
Compartment:
natural water: freshwater
DT50:
> 1 000 d
Type:
other: simple first order model (FOCUS)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
System 10 µg/L
Compartment:
natural water: freshwater
DT50:
> 1 000 d
Type:
other: simple first order model (FOCUS)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
System 10 µg/L; Calculated DT50 at 12 °C
Compartment:
natural water: freshwater
DT50:
> 1 000 d
Type:
other: simple first order model (FOCUS)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
System 100 µg/L
Compartment:
natural water: freshwater
DT50:
> 1 000 d
Type:
other: simple first order model (FOCUS)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
System 100 µg/L; Calculated DT50 at 12 °C
Transformation products:
no
Evaporation of parent compound:
no
Volatile metabolites:
no
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes

EXTRACTABLE RESIDUES
- % of applied amount at day 0: At both of the dose levels investigated the test-item remained stable under the conditions of the test. This is demonstrated by values for 14C-bromoxynil of 93.6% AR on day zero and 93.2% on day 60 for the 10 µg/L dose level. For the 100 µg/L dose level the values also changed very little over the course of the study with 101.3% AR as Bromoxynil on day zero and 97.6% AR on day 60.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: Mean (n=2) levels of volatiles were very low for both dose levels of the test item reaching a maximum value of 0.5% AR in the day 49 samples from 100 µg/L dose level. Due to the low levels of activity in the potassium hydroxide traps from flasks treated with the test item no precipitation was performed.
Results with reference substance:
Treatment checks for 14C-benzoic acid showed the applied dose to be 1.01 µg/flask, which corresponded to an initial concentration of 10.1 µg/L in the positive and solvent control flasks.
Furthermore by day 14, the recovery for the positive control samples averaged 92.5% of the applied activity, of which 86.3% was recovered as 14CO2 in the 2M potassium hydroxide traps, demonstrating the ability of the work up method to effectively trap and quantify 14CO2.
Conclusions:
The route and rate of degradation of [14C]-Bromoxynil Phenol at nominal concentrations of 10 and 100 µg/L were investigated in natural water samples incubated in the dark under aerobic conditions at a temperature of 20 ± 2 °C in accordance with the OECD Test Guideline No. 309. The study was designed as a ‘pelagic’ test as described in the Guideline. At both of the dose levels investigated the test-item remained stable under the conditions of the test. This is demonstrated by values for 14C-bromoxynil of 93.6% AR on day zero and 93.2% on day 60 for the 10 µg/L dose level. For the 100 µg/L dose level the values also changed very little over the course of the study with 101.3% AR as Bromoxynil on day zero and 97.6% AR on day 60.
Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to the Analogue Justification provided in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Compartment:
natural water: freshwater
% Total extractable:
> 100
% CO2:
0
% Recovery:
100
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 10 µg/L dose level at Day 0
Compartment:
natural water: freshwater
% Total extractable:
94.7
% CO2:
0.45
% Recovery:
95.1
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 10 µg/L dose level at Day 60
Compartment:
natural water: freshwater
% Total extractable:
> 100
% CO2:
0
% Recovery:
100
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 100 µg/L dose level at Day 0
Compartment:
natural water: freshwater
% Total extractable:
99.4
% CO2:
0.2
% Recovery:
99.6
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 100 µg/L dose level at Day 60
Parent/product:
parent
Compartment:
water
% Degr.:
0.45
Parameter:
CO2 evolution
Sampling time:
60 d
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 10 µg/L dose level after 60 days
Parent/product:
parent
Compartment:
water
% Degr.:
0.2
Parameter:
CO2 evolution
Sampling time:
60 d
Remarks on result:
other:
Remarks:
Recovered radioactivity in the 100 µg/L dose level after 60 days
Compartment:
natural water: freshwater
DT50:
> 1 000 d
Type:
other: simple first order model (FOCUS)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
System 10 µg/L
Compartment:
natural water: freshwater
DT50:
> 1 000 d
Type:
other: simple first order model (FOCUS)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
System 100 µg/L
Transformation products:
no
Conclusions:
The route and rate of degradation of [14C]-Bromoxynil Phenol at nominal concentrations of 10 and 100 µg/L were investigated in natural water samples incubated in the dark under aerobic conditions at a temperature of 20 ± 2 °C in accordance with the OECD Test Guideline No. 309. The study was designed as a ‘pelagic’ test as described in the Guideline. At both of the dose levels investigated the test-item remained stable under the conditions of the test. This is demonstrated by values for 14C-bromoxynil of 93.6% AR on day zero and 93.2% on day 60 for the 10 µg/L dose level. For the 100 µg/L dose level the values also changed very little over the course of the study with 101.3% AR as Bromoxynil on day zero and 97.6% AR on day 60.
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
5 Feb 1997 - 3 Apr 1997
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
other: BBA Guidelines for the Official Testing of Plant Protection Products, Part IV, Section 5-1
Version / remarks:
1990
Qualifier:
according to guideline
Guideline:
other: Guidance Document on Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration. Report of the FOCUS Work Group on Degradation Kinetics, EC Document Reference Sanco/10058/2005 version 2
Version / remarks:
2006
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
yes
Oxygen conditions:
aerobic/anaerobic
Inoculum or test system:
natural water / sediment: freshwater
Details on source and properties of surface water:
- Storage conditions: Both sediment/water systems were collected on 11 November 1996 and stored at ca 4 °C prior to use.
- pH at time of collection: 7.5 (sandy loam); 7.3 (clay loam)
- Hardness (CaCO3): 56.6 mg/L (sandy loam); 54.0 mg/L (clay loam)
Details on source and properties of sediment:
- Storage conditions: Both sediment/water systems were collected on 11 November 1996 and stored at ca 4 °C prior to use.
- Textural classification (i.e. %sand/silt/clay):
Sandy loam: 65.48% sand, 21.72% silt, 12.79% clay
Clay loam: 40.82% sand, 30.57% silt, 28.62% clay
- pH at time of collection:6.4 (sandy loam); 7.2 (clay loam)
- Organic carbon (%): 2.4 (sandy loam); 2.5 (clay loam)
- CEC (meq/100 g): 16.1 (sandy loam); 14.6 (clay loam)
- Biomass (mg microbial C/100 g): 10 (sandy loam); 8 (clay loam)
Duration of test (contact time):
>= 0 - <= 100 d
Initial conc.:
149 µg/L
Based on:
test mat.
Remarks:
Test system Sandy loam, viable samples
Initial conc.:
149 µg/L
Based on:
test mat.
Remarks:
Test system Clay loam, viable samples
Initial conc.:
160 µg/L
Based on:
test mat.
Remarks:
Test system Sandy loam, sterile samples
Initial conc.:
160 µg/L
Based on:
test mat.
Remarks:
Test system Clay loam, sterile samples
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: The test solution (100 µL), containing 14.9 µg (viable samples) or 16.0 µg (sterilized samples) of bromoxynil octanoate was applied to the surface of the water in each sample.
- Solubilising agent (type and concentration if used): [14C]-Bromoxynil octanoate was dissolved in acetone.
- Test temperature: 20 °C
- Continuous darkness: yes
- Any indication of the test material adsorbing to the walls of the test apparatus: No adsorption to glassware was observed for vessels containing acetonitrile.
- Other: The test samples were pre-incubated for up to 49 days in the dark at 20 ± 2°C. Equilibrium was reached after this time, as indicated by oxygen concentration, redox potential, pH and phase separation.

TEST SYSTEM
- Culturing apparatus: For each sediment type, 22 samples of sediment (including 4 for contingency purposes) were placed into individual borosilicate glass cylinders (previously silanised; 15.9 cm2 cross sectional area) to a depth of ca 2.5 cm. The corresponding surface water was added to a depth of ca 6 cm (total depth of sediment and water = ca 8.5 cm). The volume of water added was therefore equivalent to ca 100 mL.
- Method used to control oxygen conditions: A stream of moist, CO2-free air was introduced into the test system via a dip tube extending to just above the water surface (from 28 days onwards, two contingency sample dip tubes for each sediment type were lowered into the water, just below the water surface ensuring the sediment was not disturbed, in an attempt to displace dissolved 14CO2; the dip tubes were lowered into the surface water in the remaining contingency samples from 56 days onwards).
- Details of trap for CO2 and volatile organics if used: The gas mixture leaving each unit was passed through a series of 3 traps. The first trap, situated after the outlet side-arm, was a safety trap, the second contained ethanediol to trap non-specific 14C-organic volatiles and the third trap contained ethanolamine to trap liberated 14CO2. Polyurethane plugs were placed in the neck and in the safety trap of each incubation unit to trap non-specific 14C-organic volatiles.
- Other: Air entering the sterile units was passed through a filter (0.2 urn) to maintain sterility.

SAMPLING
- Sampling frequency: Duplicate incubations from each sediment type were sampled at 0 (immediately following application of test solution), 6 h, 1, 2, 7, 14, 30, 60 (study and contingency samples) and 100 (study and contingency samples) days. Sterile incubations were sampled at 30 and 100 days.
- Other: At each sampling interval, the oxygen concentration, redox potential and pH of the water (just below the air/water interface) and redox potential of the sediment (at the base of the sediment) were recorded.
Compartment:
natural water / sediment: freshwater
% Total extractable:
0.7
% Non extractable:
10.9
% CO2:
57.22
% Other volatiles:
2.37
% Recovery:
71.67
Remarks on result:
other:
Remarks:
% Recovery of the applied radioactivity after 100 days in the test system Sandy loam, viable samples
Compartment:
natural water / sediment: freshwater
% Total extractable:
2.04
% Non extractable:
18.81
% CO2:
55.44
% Other volatiles:
0.42
% Recovery:
78.1
Remarks on result:
other:
Remarks:
% Recovery of the applied radioactivity after 100 days in the test system Clay loam, viable samples
Compartment:
natural water / sediment: freshwater
% Total extractable:
46.85
% Non extractable:
6.57
% CO2:
5.6
% Other volatiles:
0.02
% Recovery:
96.06
Remarks on result:
other:
Remarks:
% Recovery of the applied radioactivity after 100 days in the test system Sandy loam, sterile samples
Compartment:
natural water / sediment: freshwater
% Total extractable:
42.86
% Non extractable:
11.74
% CO2:
5.82
% Other volatiles:
0.03
% Recovery:
94.2
Remarks on result:
other:
Remarks:
% Recovery of the applied radioactivity after 100 days in the test system Clay loam, sterile samples
Parent/product:
parent
Compartment:
total system
% Degr.:
57.22
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other:
Remarks:
14CO2 formation after 100 days in the test system Sandy loam, viable samples
Parent/product:
parent
Compartment:
total system
% Degr.:
55.44
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other:
Remarks:
14CO2 formation after 100 days in the test system Clay loam, viable samples
Parent/product:
parent
Compartment:
total system
% Degr.:
5.6
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other:
Remarks:
14CO2 formation after 100 days in the test system Sandy loam, sterile samples
Parent/product:
parent
Compartment:
total system
% Degr.:
5.82
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other:
Remarks:
14CO2 formation after 100 days in the test system Clay loam, sterile samples
Parent/product:
product
Compartment:
total system
% Degr.:
1.11
Parameter:
radiochem. meas.
Remarks:
Bromoxynil
Sampling time:
14 d
Remarks on result:
other:
Remarks:
TLC Characterisation of Radioactivity in Surface Water and Sediment Extracts of a Sandy Loam Test System Following a Single Application of Bromoxynil Octanoate
Parent/product:
product
Compartment:
total system
% Degr.:
44.81
Parameter:
radiochem. meas.
Remarks:
Bromoxynil
Sampling time:
14 d
Remarks on result:
other:
Remarks:
TLC Characterisation of Radioactivity in Surface Waters and Sediment Extracts of a Clay Loam Test System Following a Single Application of Bromoxynil Octanoate
Compartment:
natural water / sediment: freshwater
DT50:
< 2 h
Type:
not specified
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Sandy loam
Compartment:
natural water / sediment: freshwater
DT50:
4.2 h
Type:
not specified
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Sandy loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
4 h
Type:
not specified
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Clay loam
Compartment:
natural water / sediment: freshwater
DT50:
8.5 h
Type:
not specified
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Clay loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
0.074 d
Type:
other: Simple first order model (SFO), kinetic evaluation (1)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Sandy loam
Compartment:
natural water / sediment: freshwater
DT50:
0.16 d
Type:
other: Simple first order model (SFO), kinetic evaluation (1)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Sandy loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
0.16 d
Type:
other: Dual first-order in parallel model (DFOP), kinetic evaluation (1)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Clay loam
Compartment:
natural water / sediment: freshwater
DT50:
0.34 d
Type:
other: Dual first-order in parallel model (DFOP), kinetic evaluation (1)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Clay loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
2.92 d
Type:
other: Simple first order model (SFO), kinetic evaluation (2)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Sandy loam
Compartment:
natural water / sediment: freshwater
DT50:
6.2 d
Type:
other: Simple first order model (SFO), kinetic evaluation (2)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Sandy loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
12.81 d
Type:
other: Simple first order model (SFO), kinetic evaluation (2)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Clay loam
Compartment:
natural water / sediment: freshwater
DT50:
27.2 d
Type:
other: Simple first order model (SFO), kinetic evaluation (2)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Clay loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
0.07 d
Type:
other: Simple first order model (SFO), kinetic evaluation (3)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Sandy loam
Compartment:
natural water / sediment: freshwater
DT50:
0.15 d
Type:
other: Simple first order model (SFO), kinetic evaluation (3)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Sandy loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
0.5 d
Type:
other: Simple first order model (SFO), kinetic evaluation (3)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 in the test system Clay loam
Compartment:
natural water / sediment: freshwater
DT50:
1.06 d
Type:
other: Simple first order model (SFO), kinetic evaluation (3)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the test system Clay loam, based on results at 20 °C.
Compartment:
natural water / sediment: freshwater
DT50:
4 d
Type:
not specified
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 of the main degradation product 3,5-dibromo-4-hydroxybenzonitrile in Sandy loam
Compartment:
natural water / sediment: freshwater
DT50:
8.5 d
Type:
not specified
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 of the main degradation product 3,5-dibromo-4-hydroxybenzonitrile in Sandy loam, based on results at 20 °C
Compartment:
natural water / sediment: freshwater
DT50:
17 d
Type:
not specified
Temp.:
20 °C
Remarks on result:
other:
Remarks:
DT50 of the main degradation product 3,5-dibromo-4-hydroxybenzonitrile in Clay loam
Compartment:
natural water / sediment: freshwater
DT50:
36 d
Type:
not specified
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 of the main degradation product 3,5-dibromo-4-hydroxybenzonitrile in Clay loam, based on results at 20 °C
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
Details on transformation products:
- Formation and decline of each transformation product during test:
Sandy loam: The levels of bromoxynil octanoate declined rapidly in the sandy loam test system, from ca 37% at zero time to ca 10% at 6 h; parent compound was not detected in the remaining samples. The principal degradation product detected in samples cochromatographed with bromoxynil. Levels of bromoxynil increased from ca 48% at zero time to a maximum of ca 59% at 6 h, and then declined to ca 1% at 14 days. 3-Bromo-4-hydroxy-benzonitrile and 4-hydroxy-benzonithle were detected in samples from zero time to 14 days, accounting for up to 11% and 15% of applied radioactivity, respectively. Low levels of 2-bromo-4-cyanophenyl octanoate (<1%) were detected in the zero time samples. In addition, up to 7 unidentified components (each accounting for up to ca 4% of applied radioactivity) were also detected.
Clay loam: [14C]-Bromoxynil octanoate declined to 0.23% after 30 days. Bromoxynil was the principal radiolabelled degradation product, accounting for up to ca 65% of applied at 2 days; levels subsequently declined to ca 5% after 30 days. 4-Hydroxy-benzonitrile was detected in samples from 6 h to 30 days and levels increased to a maximum of ca 33% at 30 days. Low levels of 3-bromo-4-hydroxy-benzonitrile (up to ca 8%), 2-bromo-4-cyanophenyl octanoate (<1%) and up to 7 unidentified components (each accounting for up to ca 2% of applied radioactivity) were also detected.
Evaporation of parent compound:
no
Remarks:
Levels of radioactivity associated with the potyurethane plugs and ethanediol traps were generally low (up to ca 5% and ca 6% of applied radioactivity respectively).
Volatile metabolites:
no
Remarks:
Levels of radioactivity associated with the potyurethane plugs and ethanediol traps were generally low (up to ca 5% and ca 6% of applied radioactivity respectively).
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes. In the opinion of the Study Director, nothing occurred to jeopardise the scientific integrity of the study.

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed:
Sandy loam: The levels of bromoxynil octanoate declined rapidly in the sandy loam test system, from ca 37% at zero time to ca 10% at 6 h; parent compound was not detected in the remaining samples. The principal degradation product detected in samples cochromatographed with bromoxynil. Levels of bromoxynil increased from ca 48% at zero time to a maximum of ca 59% at 6 h, and then declined to ca 1% at 14 days. 3-Bromo-4-hydroxy-benzonitrile and 4-hydroxy-benzonithle were detected in samples from zero time to 14 days, accounting for up to 11% and 15% of applied radioactivity, respectively.
Clay loam: [14C]-Bromoxynil octanoate declined to 0.23% after 30 days. Bromoxynil was the principal radiolabelled degradation product, accounting for up to ca 65% of applied at 2 days; levels subsequently declined to ca 5% after 30 days. 4-Hydroxy-benzonitrile was detected in samples from 6 h to 30 days and levels increased to a maximum of ca 33% at 30 days.

MINOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed:
Sandy loam: Low levels of 2-bromo-4-cyanophenyl octanoate (<1%) were detected in the zero time samples. In addition, up to 7 unidentified components (each accounting for up to ca 4% of applied radioactivity) were also detected.
Clay loam: Low levels of 3-bromo-4-hydroxy-benzonitrile (up to ca 8%), 2-bromo-4-cyanophenyl octanoate (<1%) and up to 7 unidentified components (each accounting for up to ca 2% of applied radioactivity) were also detected.

EXTRACTABLE RESIDUES
- % of applied amount at end of study period: Levels of radioactivity associated with the sediment extracts and surface water from viable samples declined as the incubation progressed, accounting for ca 1-2% and <1% respectively, at 100 days.

NON-EXTRACTABLE RESIDUES
- % of applied amount at end of study period: Non-extractable residues in the sandy loam test system increased to a maximum of 14% (30 days) and then declined to 11% (100 days); in the clay loam test system, levels increased to a maximum of 19% at study termination.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: A concomitant increase in levels of 14CO2 recovered from the test system was observed (up to 57% at study termination).

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Levels of radioactivity associated with the potyurethane plugs and ethanediol traps were generally low (up to ca 5% and ca 6% of applied radioactivity respectively).

STERILE TREATMENTS (if used)
- Transformation of the parent compound: [14]-Bromoxynil octanoate, bromoxynil, 3-bromo-4-hydroxy-benzonitrile, 2-bromo-4-cyanophenyl octanoate and 4-hydroxy-benzonitrile were present in most of the sterilised surface waters and sediment extracts in both test systems at 30 and 100 days post-application.
Validity criteria fulfilled:
not applicable
Endpoint:
biodegradation in water: sediment simulation testing
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 Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)
Version / remarks:
1982
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Duration of test (contact time):
>= 0 - <= 26 wk
Compartment:
natural water / sediment: freshwater
% Total extractable:
1.26
% Non extractable:
6.95
% CO2:
55.24
% Other volatiles:
0.44
% Recovery:
64.89
Remarks on result:
other:
Remarks:
% Recovery of the applied radioactivity after 26 weeks
Parent/product:
parent
Compartment:
total system
% Degr.:
55.24
Parameter:
radiochem. meas.
Sampling time:
26 wk
Remarks on result:
other:
Remarks:
14CO2 formation
Compartment:
natural water / sediment: freshwater
DT50:
3.7 d
Type:
zero order
Temp.:
20 °C
Compartment:
natural water / sediment: freshwater
DT50:
7.86 d
Type:
zero order
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 based on results at 20°C
Transformation products:
yes
No.:
#1
No.:
#2
Validity criteria fulfilled:
not applicable
Conclusions:
The metabolism of [14C]-Bromoxynil Octanoate in a natural water and sediment under anaerobic conditions was investigated over a 26 week period. 14CO2 formation increased from 0.35% at 7 days to 9.79% at 28 days, 24.17% at 8 weeks and 55.70% at 26 weeks. Bromoxynil Octanoate was degraded to Bromoxynil with a half-life of 3.7 days. Further degradation to 3-Bromo-4-hydroxybenzonitrile and 4-Hydroxybenzonitrile was indicated.

Description of key information

DT50 in sediment/water system at 20 °C: <2 to 4 hours (4.2 to 8.5 hours, recalculated to 12 °C), aerobic conditions (BBA, Part IV, Section 5-1)

  

DT50 in freshwater at 20 °C: >1000 days, aerobic conditions; based RA to 3,5-dibromo-4-hydroxybenzonitrile (CAS 1689-84-5)

Key value for chemical safety assessment

Half-life in freshwater sediment:
8.5 h
at the temperature of:
12 °C

Additional information

A simulation study was carried out, according to GLP and BBA Guidelines for the Official Testing of Plant Protection Products, Part IV, Section 5-1 (1990), to investigate the fate of 2,6-dibromo-4-cyanophenyl octanoate in an aquatic model ecosystem consisting of two sediment/water systems under aerobic conditions at 20 °C. The formation of 14CO2 after 100 days accounted for 55.2 and 55.4%, respectively, of the applied radioactivity. The determined DT50 of the test compound ranged from <2 to 4 hours (4.2 to 8.5 hours, recalculated to 12 °C). In addition, three kinetic evaluations were conducted, according to FOCUS (2006), and found DT50 values ranging from 0.074 to 12.81 days (0.16 to 27.2 days, recalculated to 12 °C). The main degradation product in water and sediment was 3,5-dibromo-4-hydroxybenzonitrile, with a half-life ranging from 8.5 to 36 days (recalculated to 12 °C). The high abundance and lower degradability of the main degradation product underline its suitability as a read across substance.

 

In addition, a simulation study on the anaerobic degradation of the test substance in water/sediment following GLP and “EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)” was conducted at 20 °C. After 26 weeks 55.24% of the applied radioactivity were mineralized. The calculated half-life DT50 of the test substance was 3.7 days (7.86 days, recalculated to 12 °C).

 

Data on the degradation of 2,6-dibromo-4-cyanophenyl octanoate in surface water are not available. 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 structural analogue 3,5-dibromo-4-hydroxybenzonitrile (CAS 1689-84-5) has been applied to support the environmental hazard assessment of 2,6-dibromo-4-cyanophenyl octanoate.

In the key study, the route and rate of degradation of [14C]- 3,5-dibromo-4-hydroxybenzonitrile was investigated in natural water samples incubated in the dark under aerobic conditions at a temperature of 20 ± 2 °C in accordance with the OECD Test Guideline No. 309. At both of the dose levels investigated the test-item remained stable under the conditions of the test (DT50 = >1000 days).