2,6-dibromo-4-cyanophenyl octanoate

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 Feb 2015 - 18 Dec 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Version / remarks:

2002

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.4100 (Aerobic Soil Metabolism)

Version / remarks:

2008

Qualifier:

according to guideline

Guideline:

other: Commission Regulation (EU) No 283/2013 / DRAFT SANCO 11802/2010/rev 7 in accordance with Regulation (EC) No 1107

Version / remarks:

2009

Qualifier:

according to guideline

Guideline:

other: FOCUS, 2006: 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

Qualifier:

according to guideline

Guideline:

other: FOCUS, 2014: Generic guidance for estimating persistence and degradation kinetics from environmenatal fate studies on pesticides in EU registration. Version 1.1, 440 pp.

Version / remarks:

2014

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

other: Sandy loam, soil identification: CA soil

% Clay:

7.3

% Silt:

26.8

% Sand:

65.9

% Org. C:

0.84

pH:

6.8

CEC:

6.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.29

% Moisture content:

18.9

Soil no.:

#2

Soil type:

other: Sandy loam, soil identification: LAH soil

% Clay:

12.3

% Silt:

12.4

% Sand:

75.3

% Org. C:

1.2

pH:

6

CEC:

7.2 meq/100 g soil d.w.

Bulk density (g/cm³):

1.12

% Moisture content:

17.6

Soil no.:

#3

Soil type:

other: Silt loam, soil identification: NE soil

% Clay:

23.9

% Silt:

63.1

% Sand:

13

% Org. C:

2.2

pH:

7.3

CEC:

16.7 meq/100 g soil d.w.

Bulk density (g/cm³):

0.95

% Moisture content:

32.1

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: The soils were taken from agricultural use areas representing different geographical origin and different soil properties as required by the guidelines.
CA soil: Sanger, CA, USA
LAH soil: Laacher Hof, Germany
NE soil: Louisville, NE, USA
- Pesticide use history at the collection site:
CA soil: 2014- Glystar Plus, 2015- Gly-Star, 2015- Agromycin
LAH soil: No plant protection products used for previous 5 years.
NE soil: No plant protection products used for previous 5 years.
- Collection procedures: Sample taken with shovel and placed in plastic bag. The soils were sampled freshly from the fields (upper horizon of 0 to 20 cm) and sieved to remove rocks and plant material.
- Sampling depth (inches):
CA soil: 0 to 6
LAH soil: 0 to 8
NE soil: Louisville, NE, USA
- Storage conditions: Stored after sieving in a walk-in refrigerator.
- Storage length: 4 days before application after refrigerator conditions prior to application.
- Soil preparation (e.g., 2 mm sieved; air dried etc.): Soils were passed through a 2-mm sieve.

Soil No.:

#1

Duration:

>= 0 - <= 35 d

Soil No.:

#2

Duration:

>= 0 - <= 35 d

Soil No.:

#3

Duration:

>= 0 - <= 35 d

Soil No.:

#1

Initial conc.:

1.5 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

1.5 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#3

Initial conc.:

1.5 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

19.4 °C

Soil No.:

#2

Temp.:

19.4 °C

Soil No.:

#3

Temp.:

19.4 °C

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil preincubation conditions (duration, temperature if applicable): The untreated test systems were equilibrated to study conditions for 4 days prior to application of test substance.
- Soil condition: Soil moistures were adjusted to between pF 2.5 and 2.0 for the individual test systems by addition of Fisher Optima water.
- Soil (g/replicate): For preparation of the test systems, 50 g dry weight equivalents of the sieved soils were weighed into each flask.
- Control conditions, if used (present differences from other treatments, i.e., sterile/non-sterile, experimental conditions): The equilibrated native soil biomass test systems (BIO-) were left untreated. Equilibrated solvent control biomass test systems (BIO+) were applied with 200 µL methanol by dropwise application onto the soil surface.
- Test apparatus (Type/material/volume): The test systems consisted of a glass flask connected to a flow through system, containing traps for CO2 and organic volatile compounds.
- Details of traps for CO2 and organic volatile, if any: The test apparatus was connected to a flow through system, containing an ethylene glycol trap for volatile organics followed by two 2M potassium hydroxide traps, with tropaelin-O which indicates CO2 saturation by color change from orange to yellow, for collecting CO2, and a 1M sulfuric acid trap for volatile acids.
- Identity of co-solvent: Methanol

Test material application
- Volume of test solution used/treatment: Due to the high field application rate (560 g/ha) of bromoxynil octanoate, the treatment solution was made by mixing 14C labeled and 12C bromoxynil octanoate. To do this, 1.700 mL (4.514 mg) of 14C bromoxynil octanoate (C-1129A) was added to (4.5 mg of 12C bromoxynil octanoate (K-1322) and diluted to 24.19 mL with methanol, resulting in an application solution with a nominal concentration of 372 µg/mL (approximately 49,800,000 dpm/mL). The final concentration of this solution was determined by LSC as 390.5 µg/mL. Therefore, 200 µL applied per test system would result close to the targeted study application rate (SAR) of 75 µg per 50 g soil dry weight.
- Application method (e.g. applied on surface, homogeneous mixing etc.): 200 µL of application solution were applied dropwise onto the soil surface of the respective equilibrated test systems using a 250 µL syringe.

Any indication of the test material adsorbing to the walls of the test apparatus: No

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: Water loss from evaporation was determined by weighing all test systems at study start and the respective test systems at each sampling interval. Prior to removing the trap attachments from the test vessels for weighing, volatiles possibly still present in the head space of the test vessel were purged into the trap attachments. No significant losses of moisture were observed throughout the study.
- Continuous darkness: Yes

OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: The headspace of the test systems was continuously purged with humidified air throughout the study.

SAMPLING DETAILS
- Sampling intervals: Nine sampling intervals were distributed over the entire incubation period of 35 days. Duplicate samples were processed and analyzed at time 0, and at the following days after treatment (DAT): 0.25 (6 hr), 0.67 (16 hr), 1, 3, 7, 14, 22 and 35.
Microbial soil biomass was determined at start, middle and end of the study (DAT-0,
DAT-22, and DAT-35).
- Sampling method for soil samples: Prior to opening an incubated test system for processing of soil, volatiles possibly still present in the head space of the test system were purged into the trap attachment. Afterwards, the trap attachment was removed and the soil was extracted.

Soil No.:

#1

% Total extractable:

2.8

% Non extractable:

40.5

% CO2:

55.1

% Recovery:

98.3

Remarks on result:

other:

Remarks:

% Recovery of applied radioactivity after 35 day; CA soil

Soil No.:

#2

% Total extractable:

5.6

% Non extractable:

63.5

% CO2:

29.4

% Other volatiles:

0.2

% Recovery:

98.7

Remarks on result:

other:

Remarks:

% Recovery of applied radioactivity after 35 day; LAH soil

Soil No.:

#3

% Total extractable:

2.6

% Non extractable:

66.5

% CO2:

33.6

Remarks on result:

other:

Remarks:

102.7% Recovery of applied radioactivity after 35 day; NE soil

Parent/product:

parent

Soil No.:

#1

% Degr.:

55.1

Parameter:

radiochem. meas.

Sampling time:

35 d

Remarks on result:

other:

Remarks:

14CO2 formation in CA soil

Parent/product:

parent

Soil No.:

#2

% Degr.:

29.4

Parameter:

radiochem. meas.

Sampling time:

35 d

Remarks on result:

other:

Remarks:

14CO2 formation in LAH soil

Parent/product:

parent

Soil No.:

#3

% Degr.:

33.6

Parameter:

radiochem. meas.

Sampling time:

35 d

Remarks on result:

other:

Remarks:

14CO2 formation in NE soil

Soil No.:

#1

DT50:

0.62 d

Type:

other: Double first order in parallel (DFOP)

Temp.:

19.4 °C

Remarks on result:

other:

Remarks:

DT50 of parent compound in CA soil

Soil No.:

#1

DT50:

1.25 d

Type:

other: Double first order in parallel (DFOP)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent compound in CA soil, based on results at 19.4 °C

Soil No.:

#2

DT50:

0.61 d

Type:

other: Double first order in parallel (DFOP)

Temp.:

19.4 °C

Remarks on result:

other:

Remarks:

DT50 of parent compound in LAH soil

Soil No.:

#2

DT50:

1.23 d

Type:

other: Double first order in parallel (DFOP)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent compound in LAH soil, based on results at 19.4 °C

Soil No.:

#3

DT50:

0.14 d

Type:

other: Double first order in parallel (DFOP)

Temp.:

19.4 °C

Remarks on result:

other:

Remarks:

DT50 of parent compound in NE soil

Soil No.:

#3

DT50:

0.28 d

Type:

other: Double first order in parallel (DFOP)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent compound in NE soil, based on results at 19.4 °C

Soil No.:

#1

DT50:

0.58 d

Type:

other: Dual first-order in parallel model (DFOP)

Temp.:

20 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation using FOCUS; CA soil

Soil No.:

#1

DT50:

1.23 d

Type:

other: Dual first-order in parallel model (DFOP)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation using FOCUS; Calculated DT50 based on results at 20 °C, CA soil

Soil No.:

#2

DT50:

0.47 d

Type:

other: Dual first-order in parallel model (DFOP)

Temp.:

20 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation using FOCUS; LAH soil

Soil No.:

#2

DT50:

1 d

Type:

other: Dual first-order in parallel model (DFOP)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation using FOCUS; Calculated DT50 based on results at 20 °C, LAH soil

Soil No.:

#3

DT50:

0.12 d

Type:

other: First-order multi-compartment (FOMC)

Temp.:

20 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation using FOCUS; NE soil

Soil No.:

#3

DT50:

0.25 d

Type:

other: First-order multi-compartment (FOMC)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation using FOCUS; Calculated DT50 based on results at 20 °C, NE soil

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on transformation products:

- Formation and decline of each transformation product during test:
Extractable residues decreased from DAT-0 to DAT-35 from 98.0 to 2.8% AR in CA soil, from 98.1 to 5.6% AR in LAH soil, and from 100.8 to 2.6% AR in NE soil. The amount of bromoxynil octanoate in CA soil decreased from 93.7% at DAT-0 to approximately 2% at DAT-7 and DAT-14 and then declined to below the limit of detection (LOD) after DAT-14. The amount of bromoxynil octanoate in LAH soil decreased from 92.8% at DAT-0 to 1.7% at DAT-35. The amount of bromoxynil octanoate in NE soil decreased from 82.4% at DAT-0 to 0.8% at DAT-7, and then declined to below the LOD after DAT-7. Degradation of bromoxynil octanoate was accompanied by the formation of three degradation products. Bromoxynil-phenol occurred at maximum levels of 36.4% at DAT-0.67 in CA soil, 24.8% at DAT-0.67 in LAH soil, and 42.3% AR at DAT-0.25 in NE soil. The major degradate 3,5-dibromo-4-hydroxybenzamide occurred at maximum levels of 14.1% in CA soil at DAT-3, 13.1% in LAH soil at DAT-0.67 and 32.4% AR at DAT-0.67 in NE soil. The degradate 3,5-dibromo-4-hydroxybenzoic acid occurred at maximum levels of with 6.8% in CA soil at DAT-3, 3.5% in LAH soil at DAT-0.67 and 7.2% AR at DAT-1 in NE soil. The total unidentified residues amounted to a maximum of 1.9% AR and no single component exceeded 1.9% AR at any sampling interval for all soils.
- Pathways for transformation: Based on the results of the study, the proposed pathway for the degradation of [phenyl-UL-14C]bromoxynil octanoate in soil under aerobic conditions involves the following possible processes: Ester cleavage of bromoxynil octanoate, resulting in the formation of bromoxynilphenol; Stepwise hydrolysis of the nitrile of bromoxynil-phenol, resulting in the formation of 3,5-dibromo-4-hydroxybenzamide and 3,5-dibromo-4-hydroxybenzoic acid; Mineralization (carbon dioxide formation); Formation of non-extractable residues.

Evaporation of parent compound:

no

Remarks:

Formation of volatile organic compounds was insignificant as demonstrated by values of = 0.6% applied radioactivity at all sampling intervals in all soils.

Volatile metabolites:

no

Remarks:

Formation of volatile organic compounds was insignificant as demonstrated by values of = 0.6% applied radioactivity at all sampling intervals in all soils.

Details on results:

TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes. No significant loss of moisture was observed throughout the study. Additionally, microbial evaluations showed that soils were biologically active.

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Degradation of bromoxynil octanoate was accompanied by the formation of three degradation products. Bromoxynil-phenol occurred at maximum levels of 36.4% at DAT-0.67 in CA soil, 24.8% at DAT-0.67 in LAH soil, and 42.3% AR at DAT-0.25 in NE soil. The major degradate 3,5-dibromo-4-hydroxybenzamide occurred at maximum levels of 14.1% in CA soil at DAT-3, 13.1% in LAH soil at DAT-0.67 and 32.4% AR at DAT-0.67 in NE soil. The degradate 3,5-dibromo-4-hydroxybenzoic acid occurred at maximum levels of with 6.8% in CA soil at DAT-3, 3.5% in LAH soil at DAT-0.67 and 7.2% AR at DAT-1 in NE soil. The total unidentified residues amounted to a maximum of 1.9% AR and no single component exceeded 1.9% AR at any sampling interval for all soils.

EXTRACTABLE RESIDUES
- % of applied amount at end of study period: Extractable residues decreased from DAT-0 to DAT-35 from 98.0 to 2.8% AR in CA soil, from 98.1 to 5.6% AR in LAH soil, and from 100.8 to 2.6% AR in NE soil.

NON-EXTRACTABLE RESIDUES
- % of applied amount at end of study period: In CA soil, non-extractable residues (NER) increased from 0.8% at DAT-0 to 51.5% AR at DAT-7 in and then declined to 40.5% AR by DAT-35 (end of study). In LAH soil, NER increased from 1.0% at DAT-0 to 75.2% AR at DAT-7 and declined to 63.5% AR at DAT-35. In NE soil, NER increased from 1.1% at DAT-0 to 69.0% AR in at DAT-7 then declined to 66.5% AR at DAT-35.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: The maximum amount of carbon dioxide was 55.5%, 29.4% and 33.6% AR in CA soil, LAH soil and NE soil, respectively.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Formation of volatile organic compounds was insignificant as demonstrated by values of = 0.6% applied radioactivity at all sampling intervals in all soils.

Reference 2

Endpoint:

biodegradation in soil: 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:

other: US EPA Pesticide Assessment Guidelines Subdivision N, 162-1

Version / remarks:

1982

Qualifier:

according to guideline

Guideline:

other: FOCUS, 2006: 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

Qualifier:

according to guideline

Guideline:

other: FOCUS, 2014: Generic guidance for estimating persistence and degradation kinetics from environmenatal fate studies on pesticides in EU registration. Version 1.1, 440 pp.

Version / remarks:

2014

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil no.:

#1

Soil type:

sandy loam

% Clay:

10.4

% Silt:

20.8

% Sand:

68.8

% Org. C:

2.1

pH:

6.7

CEC:

6.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.43

% Moisture content:

10.86

Soil No.:

#1

Duration:

>= 0 - <= 90 d

Soil No.:

#1

Initial conc.:

5.96 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

21 ± 2 °C

Soil No.:

#1

% Total extractable:

10.85

% Non extractable:

13.59

% CO2:

64.28

% Other volatiles:

0.35

% Recovery:

89.47

Remarks on result:

other:

Remarks:

% Recovery of applied radioactivity after 90 days

Parent/product:

parent

Soil No.:

#1

% Degr.:

64.28

Parameter:

CO2 evolution

Sampling time:

90 d

Remarks on result:

other:

Remarks:

14CO2 formation

Soil No.:

#1

DT50:

2 d

Type:

not specified

Temp.:

21 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance

Soil No.:

#1

DT50:

4.65 d

Type:

not specified

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent compound, based on results at 20 °C

Soil No.:

#1

DT50:

1.37 d

Type:

other: Simple first order model (SFO)

Temp.:

20 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation (1) using FOCUS

Soil No.:

#1

DT50:

2.91 d

Type:

other: Simple first order model (SFO)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation (1) using FOCUS; Calculated DT50 based on results at 20 °C

Soil No.:

#1

DT50:

1.37 d

Type:

other: Simple first order model (SFO)

Temp.:

20 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation (2) using FOCUS

Soil No.:

#1

DT50:

2.91 d

Type:

other: Simple first order model (SFO)

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Kinetic evaluation (2) using FOCUS; Calculated DT50 based on results at 20 °C

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

Conclusions:

The objective of this study was to Investigate the metabolism of [14C]-Bromoxynil Octanoate in soil under aerobic conditions. This study was performed to meet the US Pesticide Assessment Guidelines Subdivision N, 162-1.
Cyano-labelled [14C]-Bromoxynil Octanoate was Incubated aerobically in a sandy loam soil. 14C-labelled carbon dioxide [14CO2], organic volatile evolution and levels of radioactivity in the soil were determined throughout the Incubation period. Profiles of radiolabelled components were also examined. Overall mean recoveries ranged from 87.11% to 103.86% over a 90 day Incubation period. 14CO2 evolution increased with the duration of incubation rising to 64.28% at 90 days. Organic volatile evolution was low (<5%). Extractable radioactivity decreased with incubation time decreasing from 103.35% at zero time to 10.85% at 90 days. However a proportionate increase in bound residues was not observed as bound radioactivity at 90 days only accounted for 13.59% of the applied dose. Degradate profiling, using high performance liquid chromatography, (HPLC) Indicated that [14C]-Bromoxynil Octanoate rapidly degraded to several components. The principal degradate co-chromatographed with brotnoxynil, although low levels of components chromatographically similar to 3-bromo-4-hydroxy benzamide, 3,5-dibromo-4-hydroxy benzamide and 3,5-dibromo-4-hydroxy benzole add were also detected. The relative contribution of these degradates decreased with increased incubation time, indicating that further degradation, to 14CO2, had resulted.
Under the conditions used in this study, the half-life for [14C]-Bromoxynil Octanoate was calculated to be 2 days.

Reference 3

Endpoint:

biodegradation in soil: simulation testing

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:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

no

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

loam

% Clay:

25

% Silt:

29

% Sand:

46

% Org. C:

1.59

pH:

7.4

CEC:

21.7 meq/100 g soil d.w.

% Moisture content:

2.6

Soil no.:

#2

Soil type:

clay loam

% Clay:

31

% Silt:

26

% Sand:

43

% Org. C:

1.45

pH:

6.6

CEC:

19.4 meq/100 g soil d.w.

% Moisture content:

2.1

Soil no.:

#3

Soil type:

loamy sand

% Clay:

11

% Silt:

4

% Sand:

85

% Org. C:

2.97

pH:

7.34

CEC:

15.65 meq/100 g soil d.w.

% Moisture content:

1.2

Soil no.:

#4

Soil type:

sandy loam

% Clay:

15

% Silt:

15

% Sand:

70

% Org. C:

1.42

pH:

6.67

CEC:

7.65 meq/100 g soil d.w.

% Moisture content:

0.86

Soil No.:

#1

Duration:

>= 0 - <= 10 d

Soil No.:

#2

Duration:

>= 0 - <= 10 d

Soil No.:

#3

Duration:

>= 0 - <= 10 d

Soil No.:

#4

Duration:

>= 0 - <= 10 d

Soil No.:

#1

Initial conc.:

2 ppm

Based on:

test mat.

Soil No.:

#2

Initial conc.:

2 ppm

Based on:

test mat.

Soil No.:

#3

Initial conc.:

2 ppm

Based on:

test mat.

Soil No.:

#4

Initial conc.:

2 ppm

Based on:

test mat.

Parameter followed for biodegradation estimation:

test mat. analysis

Soil No.:

#1

Temp.:

10 °C

Soil No.:

#1

Temp.:

22 °C

Soil No.:

#2

Temp.:

10 °C

Soil No.:

#2

Temp.:

22 °C

Soil No.:

#3

Temp.:

10 °C

Soil No.:

#3

Temp.:

22 °C

Soil No.:

#4

Temp.:

10 °C

Soil No.:

#4

Temp.:

22 °C

Soil No.:

#1

DT50:

18.76 d

Type:

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

Temp.:

10 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Loam soil

Soil No.:

#1

DT50:

7.11 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Loam soil

Soil No.:

#1

DT50:

18.1 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent substance, based on results at 22 °C; Loam soil

Soil No.:

#2

DT50:

20.22 d

Type:

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

Temp.:

10 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Clay-loam soil

Soil No.:

#2

DT50:

10.62 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Clay-loam soil

Soil No.:

#2

DT50:

27.04 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent substance, based on results at 22 °C; Clay-loam soil

Soil No.:

#3

DT50:

34.07 d

Type:

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

Temp.:

10 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Loamy-sand soil

Soil No.:

#3

DT50:

15.07 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Loamy-sand soil

Soil No.:

#3

DT50:

38.37 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent substance, based on results at 22 °C; Loamy-sand soil

Soil No.:

#4

DT50:

28.65 d

Type:

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

Temp.:

10 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Sandy-loam soil

Soil No.:

#4

DT50:

18.7 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance; Sandy-loam soil

Soil No.:

#4

DT50:

47.62 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent substance, based on results at 22 °C; Sandy-loam soil

Conclusions:

This report describes a study carried out to determine the rate of degradation of bromoxynil octanoate in loam, clay-loam, loamy-sand and sandy-loam soils at 10°C and 22°C. The soil, at approximately 50% of its maximum moisture capacity, was treated with bromoxynil octanoate at approximately 2 ppm (on a dry weight basis) equivalent to an application rate of 0.4 kg a.i./ha in the top 2 cm of soil. The soil was incubated for up to 10 days after treatment and was sampled at intervals. Each sample was then subjected to an extraction procedure designed to isolate unchanged bromoxynil octanoate. The bromoxynil octanoate was determined using gas liquid chromatography.
The results of this study indicate that bromoxynil octanoate was rapidly metabolised at 10°C and 22°C in the four soils used. At 10°C and 22°C the half-life of the ester was found to be 18.76h and 7.11h for loam, 20.22h and 10.62h for clay-loam, 34.07h and 15.07h for loamy-sand and 28.65h and 18.70h for sandy-loam respectively.

Reference 4

Endpoint:

biodegradation in soil: 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:

other: EC Directive 95/36/EC, Active Substances, Section 7.1.1.1.2 (July 1995) and SETAC Procedures for assessing the Environmental Fate and Ecotoxicity of Pesticides, Section 1.2

Version / remarks:

1995

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Oxygen conditions:

anaerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

15

% Silt:

32

% Sand:

53

% Org. C:

2.1

pH:

7.1

CEC:

9.1 meq/100 g soil d.w.

% Moisture content:

28.56

Soil No.:

#1

Duration:

>= 0 - <= 121 d

Soil No.:

#1

Initial conc.:

0.82 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20 ± 2 °C

Microbial biomass:

547.82 µg C/g soil

Soil No.:

#1

% Total extractable:

3.1

% Non extractable:

14.3

% CO2:

68.2

% Other volatiles:

0.3

% Recovery:

87.6

Remarks on result:

other:

Remarks:

% Recovery of applied radioactivity after 121 days

Parent/product:

parent

Soil No.:

#1

% Degr.:

68.2

Parameter:

CO2 evolution

Sampling time:

121 d

Remarks on result:

other:

Remarks:

% Mineralisation of applied radioactivity

Soil No.:

#1

DT50:

0.5 d

Temp.:

20 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance

Soil No.:

#1

DT50:

1.06 d

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent substance, based on results at 20 °C

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Conclusions:

The anaerobic soil metabolism of [14C]-phenyl ring labelled bromoxynil octanoate has been investigated in a sandy loam soil with bromoxynil octanoate applied at a field rate of 0.818 kg/ha. This is equivalent to a field rate of bromoxynil phenol of 0.562 kg/ha.
The samples were incubated in the dark at 20 ± 2 °C. After treatment they were purged continuously with nitrogen during the 121-day incubation period. Effluent gases were passed through a foam bung to trap high molecular weight volatiles, ethanediol to trap polar volatiles and two 2 M sodium hydroxide solutions to trap carbon dioxide. The effluent gasses from an additional five units were passed through two 2 M sodium hydroxide solution traps, a catalytic converter (to convert methane to carbon dioxide) and a further two 2 M sodium hydroxide traps (to trap any carbon dioxide formed in the catalytic converter). The redox potential of the soil was measured in two control flasks prior to test article application to confirm that anaerobic conditions (redox potential <200 mV) had been established. Soil samples were taken for analysis at zero time and 1, 3, 7, 14, 29, 58 and 121 days after application.
Radioactivity extracted from soil in acetonitrile and acetonitrile : water (1:1 v/v) decreased from a maximum of 44% of applied radioactivity initially to 2% at 121 days. Soxhlet extractions with acetonitrile : water (4:1 v/v) of samples containing >10% of applied radioactivity unextracted (i.e., 29, 58 and 121-day samples) recovered an additional 1 to 3% of applied radioactivity. During the incubation period, the bromoxynil octanoate concentration in the total system decreased rapidly from 96% of applied radioactivity, initially, to <1% at 7 days. Three major metabolites were formed, bromoxynil, benzoic acid and 3-bromo-4-hydroxybenzonitrile (RPA722852). The DT-50 value (half life) of bromoxynil octanoate was 0.5 days, and the DT-90 was 1.7 days. Bromoxynil octanoate was degraded to carbon dioxide (68% at 121 days) and methane (up to 17% at 121 days).

Reference 5

Endpoint:

biodegradation in soil: 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:

other: EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

anaerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

silt loam

% Clay:

25.6

% Silt:

64

% Sand:

10.4

pH:

5.9

CEC:

9.7 meq/100 g soil d.w.

Soil No.:

#1

Duration:

>= 0 - <= 12 mo

Soil No.:

#1

Initial conc.:

1 ppm

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

22 - 24 °C

Soil No.:

#1

% Total extractable:

1.9

% Non extractable:

24.8

% Other volatiles:

72.9

% Recovery:

100

Remarks on result:

other:

Remarks:

% Of recovered radioactivity, after 12 month, normalized to the total recovered radioactivity

Soil No.:

#1

DT50:

< 1 d

Temp.:

>= 22 - <= 24 °C

Remarks on result:

other:

Remarks:

DT50 of the parent compound

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

No.:

#6

Conclusions:

Forty (40) gram samples of the soil, in individual flasks, were flooded with 100 mL of water and aged for 1 month prior to fortification. After aging, each soil sample was fortified with 1.0 ppm of 14C bromoxynil octanoate. The soil/water samples were purged with nitrogen and placed in soil cabinets in the dark at a constant temperature between 22 - 24° C for the duration of the study. The flasks were periodically purged with nitrogen in order to maintain anaerobicity and collect volatiles in a series of traps. Test samples were taken at 0,1, 3, 7,14, 21, and 28 days; 2, 4, 6,10 and 12 months. Where possible, the extracts were analyzed by thin-layer chromatography in an attempt to identify the compounds present.
The parent compound, bromoxynil octanoate, hydrolyzed rapidly in water to the phenol with a half-life of <1 day. Significant amounts of 14C activity began to appear in the NaOH/C02 traps at 14 days. At this point in time 3% of the total residue in the sample was found to be in the form of volatile products. This percentage steadily increased to 73% of the total sample residue at 12 months. In the interval between 4 months and 12 months the majority of the 14C residue in the sample was found to be in the form of volatile products. These residues represented between 17 & 18% of the initial dose.
Degradation products together represented an amount equivalent to 1.7% of the initial bromoxynil octanoate concentration.

Reference 6

Endpoint:

biodegradation in soil: 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:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Version / remarks:

2002

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic/anaerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

17

% Silt:

26

% Sand:

57

% Org. C:

1.1

pH:

7.6

CEC:

10.7 meq/100 g soil d.w.

Bulk density (g/cm³):

1.2

% Moisture content:

5.22

Soil No.:

#1

Duration:

>= 0 - <= 126 d

Soil No.:

#1

Initial conc.:

2.19 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20 ± 2 °C

Microbial biomass:

343.4 µg C/g soil

Soil No.:

#1

% Total extractable:

55.99

% Non extractable:

20.76

% CO2:

14.66

% Recovery:

91.4

Remarks on result:

other:

Remarks:

% Recovery of the applied radioactivity after 122 days of anaerobic incubation

Parent/product:

parent

Soil No.:

#1

% Degr.:

14.66

Parameter:

CO2 evolution

Sampling time:

122 d

Remarks on result:

other:

Remarks:

% Of applied radioactivity as 14CO2 evolution, after 122 days of anaerobic incubation

Soil No.:

#1

DT50:

0.9 d

Type:

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

Temp.:

20 °C

Remarks on result:

other:

Remarks:

DT50 of parent substance

Soil No.:

#1

DT50:

1.91 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of parent substance, based on results at 20 °C

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

No.:

#6

Conclusions:

Following aging of [14C]-bromoxynil octanoate in a sandy loam soil under aerobic conditions the route and rate of degradation of 14C-residues including the rapidly formed metabolite bromoxynil phenol have been investigated under anaerobic conditions at 20 ± 2°C in the dark. The test system consisted of 100 g of soil (oven dried equivalent) in straight-sided, conical flasks put into a flow through system. The individual flasks were connected to a series of traps for the collection of volatile organic compounds and 14CO2. Following treatment with [14C]-bromoxynil octanoate at an application rate equivalent to 2.19 mg/kg. Treated samples were incubated under aerobic conditions, at a soil moisture content of 17 g per 100 g of soil, for 3 days. Anaerobic conditions were established by adding nitrogen-purged de-ionised water to an approximate depth of 2 cm above the soil surface, followed by a continuous flow of nitrogen through the flasks for 122 days. At intervals of 0 and 3 days during the aerobic phase, and at 1, 3, 7, 14, 31, 61, 90 and 122 days after waterlogging, duplicate flasks and their corresponding traps were removed from the incubation system. Following quantification of radioactivity by LSC, components in the water and soil extracts were analysed by HPLC and TLC. In addition confirmation of structural identity of metabolites was performed for selected extracts by LC/MS. The non-extractable radioactivity in the soil was quantified by combustion/LSC.
The overall recoveries ranged from 90.6 to 100.8% for individual samples with a mean value of 95.5% of applied radioactivity (AR). The total volatile Radioactivity (14CO2) generated during the anaerobic phase had reached 14.7% at the end of the study. An initial lag phase in the production of volatile radioactivity was seen up to 60 days of anaerobic incubation where only 3-4% was produced. The half-life of bromoxynil octanoate was 0.9 days.

Description of key information

DT50 = 0.14 to 0.62 days (0.28 to 1.25 days, recalculated to 12 °C), 29.4 – 55.1% degradation after 35 days, aerobic conditions (OECD 307)

Key value for chemical safety assessment

Half-life in soil:

1.25 d

at the temperature of:

12 °C

Additional information

A simulation study on the biodegradation of 14C-labelled 2,6-dibromo-4-cyanophenyl octanoate in three different soils (sandy loam, sandy loam and silt loam) was investigated, following GLP and OECD Guideline 307. At 19.4 °C the test substance degraded with a half-life of 0.14 – 0.62 days (0.28 – 1.25 days, recalculated to 12 °C). After 35 days 29.4 – 55.1% of the applied radioactivity were mineralized. In addition, a kinetic evaluations was conducted, according to FOCUS (2006, 2014), and found DT50 values ranging from 0.12 to 0.58 days (0.25 to 1.23 days, recalculated to 12 °C).

 

Another simulation study, according to GLP and “US EPA Pesticide Assessment Guidelines Subdivision N, 162-1”, investigated the degradation of the test substance in one test soil under aerobic conditions at 21 °C. After 90 days 64.28% of the applied radioactivity was found as 14CO2. The DT50 of the test substance was 2.0 days (4.65 days, recalculated to 12 °C). Additionally, two kinetic evaluations were conducted, according to FOCUS (2006, 2014), and determined a half-life of 1.37 days (2.91 days, recalculated to 12 °C).

 

A third study assessed the biodegradation of 2,6-dibromo-4-cyanophenyl octanoate in four different soils (loam, clay loam, loamy sand, sandy loam), following GLP. The DT50 of the test substance was 18.76 – 34.07 days at 10 °C and 7.11 – 18.70 days at 22 °C (18.10 – 47.62 days, recalculated to 12 °C based on results at 22 °C).

 

Three additional GLP and guideline studies investigated the anaerobic degradation of 2,6-dibromo-4-cyanophenyl octanoate in soil. After 121 and 126 days 68.2 and 14.7% of the applied radioactivity was found as 14CO2. The determined half-life of the test substance at 20 °C was 0.5 – 0.9 days (1.06 – 1.91 days, recalculated to 12 °C).