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Environmental fate & pathways

Biodegradation in soil

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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.
Endpoint:
biodegradation in soil: simulation testing
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
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
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
Deviations:
yes
Remarks:
The test duration of the study with the target substance was only 7 days.
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 in accordance with Regulation (EC) No 1107/2009
Version / remarks:
2009
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 2.0
Version / remarks:
2006
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:
sandy loam
% Clay:
9
% Silt:
19
% Sand:
72
% Org. C:
2
pH:
6.5
CEC:
9 meq/100 g soil d.w.
Bulk density (g/cm³):
1.21
Soil No.:
#1
Duration:
7 d
Soil No.:
#1
Initial conc.:
2.15 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#1
% Total extractable:
26.5
% Non extractable:
68.5
% CO2:
16
% Other volatiles:
0.1
Remarks on result:
other:
Remarks:
Total recovery: 101.0 % of applied radioactivity; At day 7
Parent/product:
parent
Soil No.:
#1
% Degr.:
16
Parameter:
radiochem. meas.
Sampling time:
7 d
Remarks on result:
other:
Remarks:
14CO2 formation
Soil No.:
#1
DT50:
0.7 d
Type:
other: Double first order in parallel (DFOP)
Temp.:
19.6 °C
Soil No.:
#1
DT50:
1.4 d
Type:
other: Double first order in parallel (DFOP)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
DT50 calculated based on results at 19.6 °C.
Soil No.:
#1
DT50:
0.97 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Kinetic evaluation (1) using FOCUS 2006
Soil No.:
#1
DT50:
2.1 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Kinetic evaluation (1) using FOCUS 2006; DT50 recalculated to 12 °C
Soil No.:
#1
DT50:
0.85 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Kinetic evaluation (2) using FOCUS 2006
Soil No.:
#1
DT50:
1.8 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Kinetic evaluation (2) using FOCUS 2006; DT50 recalculated to 12 °C
Soil No.:
#1
DT50:
0.85 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Kinetic evaluation (3) using FOCUS 2006
Soil No.:
#1
DT50:
1.8 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Kinetic evaluation (3) using FOCUS 2006; DT50 recalculated to 12 °C
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
Conclusions:
The route and rate of degradation of [phenyl-UL-14C]bromoxynil heptanoate were studied in one soil under aerobic conditions in the dark in the laboratory for 7 days at 19.6 °C and 54.9% of the maximum water holding capacity.
A study application rate of 2.15 mg bromoxynil heptanoate per kg soil dry weight was applied. The test was performed in static systems consisting of Erlenmeyer flasks each containing 100 g soil (dry weight equivalents) and equipped with traps for the collection of carbon dioxide and volatile organic compounds.
The mean material balance was 98.8% AR (range from 95.7 to 101.0% AR). The maximum amount of carbon dioxide was 16.0% AR at study end (DAT-7). Formation of other volatile organic compounds (VOC) was insignificant as demonstrated by values of = 0.1% AR at all sampling intervals.
Besides the formation of carbon dioxide, three degradation products were identified with the following maximum amounts: bromoxynil-phenol with 31.7% AR at DAT-2, 3,5-dibromo-4-hydroxybenzamide with 10.6% AR at DAT-2 and 3,5-dibromo-4-hydroxybenzoic acid with 4.5% AR at DAT-2. The total unidentified residues amounted to a maximum of 1.6% AR and no single component exceeded 1.6% AR at any sampling interval.
The experimental data could be well described by a double first order in parallel (DFOP) kinetic model. The half-life of bromoxynil heptanoate under aerobic conditions was 0.7 days.

The kinetic evaluations, according to FOCUS (2006), of the presented study (Störch, K. and Kasel, D. 2014) revealed DT50 values from 0.85 – 0.97 (1.8 – 2.1 days, recalculated to 12 °C).

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); based on RA to 2,6-dibromo-4-cyanophenyl octanoate (CAS 1689-99-2)

Key value for chemical safety assessment

Half-life in soil:
1.25 d
at the temperature of:
12 °C

Additional information

Reliable data on the biodegradation of 2,6-dibromo-4-cyanophenyl heptanoate (CAS 56634-95-8) is 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), the assessment was based on reliable and adequate read-across data available for the structural analogue 2,6-dibromo-4-cyanophenyl octanoate (CAS 1689-99-2).

 

The fate of the read-across substance 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).

 

A simulation study the biodegradation of 14C-labelled 2,6-dibromo-4-cyanophenyl heptanoate in a sandy loam soil was investigated, following GLP and OECD Guideline 307 with acceptable restrictions. At 20 °C the test substance degraded with a half-life of 0.7 days (1.4 days, recalculated to 12 °C). After 7 days 16% of the applied radioactivity was mineralized.