2,6-dibromo-4-cyanophenyl octanoate

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Version / remarks:

2000

Qualifier:

according to guideline

Guideline:

other: US EPA Subdivision N, Section 163-1

Version / remarks:

1982

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Analytical monitoring:

yes

Details on sampling:

- Concentrations: The target nominal concentrations were 0.05, 0.025, 0.0125, 0.005 and 0.00125 mg/L [14C]-Bromoxynil Octanoate.
- Sampling interval: The soil solutions were mixed and slurried for approximately 30 minutes on an end-over-end shaker before samples were taken.
- Sample storage before analysis: Supernatants, solvent extracts and soil residues were stored at ca 5°C in the dark. Stock solutions, treatment solutions and standards were all stored at ca <-15°C in the dark. All samples analysed during the preliminary experiments were profiled by HPLC within 1 day of generation. In the definitive phase and adsorption trial experiment, supernatants and extracts were analysed immediately following sample generation.

Matrix no.:

#1

Matrix type:

other: Longwoods Sandy Loam

% Clay:

15

% Silt:

8

% Sand:

77

% Org. carbon:

1.3

pH:

7.4

CEC:

12.4 meq/100 g soil d.w.

Bulk density (g/cm³):

1.29

Matrix no.:

#2

Matrix type:

other: Farditch Silt Loam

% Clay:

17

% Silt:

54

% Sand:

29

% Org. carbon:

3.45

pH:

6

CEC:

12.5 meq/100 g soil d.w.

Bulk density (g/cm³):

0.94

Matrix no.:

#3

Matrix type:

other: Lockington Clay Loam

% Clay:

37

% Silt:

21

% Sand:

42

% Org. carbon:

2.76

pH:

5.5

CEC:

24.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.15

Matrix no.:

#4

Matrix type:

other: Calke Sandy Loam

% Clay:

10

% Silt:

15

% Sand:

75

% Org. carbon:

3.56

pH:

5.9

CEC:

12.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.13

Matrix no.:

#5

Matrix type:

other: South Witham Clay Loam

% Clay:

35

% Silt:

26

% Sand:

39

% Org. carbon:

3.8

pH:

7.6

CEC:

27.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.18

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
Longwoods: Site I2, Longwoods Quarry, Lincolnshire, UK.
Farditch Farm: Site E1, Farditch Farm, Chelmorton, Derbyshire, UK.
Lockington: Site G2, Lockington Grounds Farm, Leicestershire, UK.
Calke: Site D, Calke, Derbyshire, UK.
South Witham: Site J2, South Witham Quarry, South Witham, Lincolnshire, UK.
- Collection procedures: The soils were; Longwoods sandy loam, collected on 10 November 2010; Farditch silt loam collected on 12 November 2010; Lockington clay loam collected on 26 June 2003; Calke sandy loam collected on 02 June 2011 and South Witham clay loam collected on 07 June 2011.
- Sampling depth (cm):
Longwoods: 5-20 cm
Farditch Farm: 10-20 cm
Lockington: 9-15 cm
Calke: 5-18 cm
South Witham: 5-20 cm
- Storage conditions: The soils were stored, in the dark, at a temperature of ca 4 °C.
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): The soils were dried slightly if needed, before being passed through a 2 mm sieve and fully characterised, with respect to particle size distribution, cation exchange capacity/exchangeable cations, organic matter content, pH, bulk density and water holding capacity. All soils were sterilised by gamma irradiation (single dose of 25-45 kGy) once prior to use for the preliminary and later prior to use in the definitive test. The soils were stored, in the dark, at a temperature of ca 4 °C.

PROPERTIES
- Soil texture: See Table “Matrix properties”
- Soil classification system: USDA Textural Class
- Extractable Cations (Ca, Mg, Na, K, H) (MEQ/100 g):
Longwoods: Calcium 80.6%, Magnesium 2.6%, Sodium 0.4%, Potassium 1.5%, Hydrogen 14.9%
Farditch Farm: Calcium 51.2%, Magnesium 2.7%, Sodium 0.5%, Potassium 0.8%, Hydrogen 44.8%
Lockington: Calcium 69.7%, Magnesium 6.9 %, Sodium 0.5%, Potassium 0.6%, Hydrogen 22.3%
Calke: Calcium 62.2%, Magnesium 4.5%, Sodium 0.5%, Potassium 0.9%, Hydrogen 31.9%
South Witham: Calcium 80.4%, Magnesium 4.9 %, Sodium 0.7%, Potassium 5.0%, Hydrogen 8.9%
- Moisture at 1/3 atm (%):
Longwoods: 8.4
Farditch Farm: 27.7
Lockington: 23.4
Calke: 17.0
South Witham: 24.7

Details on test conditions:

TEST CONDITIONS
- pH: The pH of the calcium chloride solutions (sterilised by filtration) used during this study was found to be in the range 6.1 to 6.3. The pH range with soil but without test item was 6.6 to 7.6 (control samples.

TEST SYSTEM
- Type, size and further details on reaction vessel: PTFE tubes (ca 50 mL capacity) were selected for use in the definitive phase of the study. All tubes were weighed before and after addition of soil (where appropriate) and then after addition of aqueous 0.01 M calcium chloride solution. The calcium chloride solutions were all prepared using the dihydrate (CaCl2.2H2O) and the pH measured before use. All sample tubes were shaken in the dark, on an end-over-end shaker (unless otherwise specified), at a temperature of 20 ± 2°C.
- Amount of soil/sediment/sludge and water per treatment (if simulation test): Approximately 5 g ode for each soil was weighed into pre-weighed PTFE tubes. The tubes were capped and re-weighed. Calcium chloride solution (25 mL less the moisture content of the soil) was added and the mixture was shaken for ca 16 hours to pre equilibrate prior to treatment.
- Soil/sediment/sludge-water ratio (if simulation test): For each concentration and each soil a 1:5 soil to solution ratio was prepared.
- Number of reaction vessels/concentration: Duplicate tubes for each concentration and each soil were prepared.

Sample No.:

#1

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.05 other: mg/L

Temp.:

20 °C

Sample No.:

#2

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.05 other: mg/L

Temp.:

20 °C

Sample No.:

#3

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.05 other: mf/L

Temp.:

20 °C

Sample No.:

#4

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.05 other: mg/L

Temp.:

20 °C

Sample No.:

#5

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.05 other: mg/L

Temp.:

20 °C

Computational methods:

- Adsorption and desorption coefficients (Kd): The amount of [14C]-Bromoxynil Octanoate adsorbed to the soil is calculated as the difference between the amount applied (µg) and that found in the aqueous phase. As a quantity of aqueous solution (residual water) remains in the soil pellet following centrifugation, an allowance is made for this. The amount of residual water is calculated using the equation: R1 = Ws – Wode; with R1 = Residual water 1 (g), Ws = Weight of soil pellet after removal of supernatant (g), Wode = Weight of oven dried equivalent soil (g).
- Freundlich adsorption and desorption coefficients: The Freundlich adsorption constant (Kf ) and (1/n) for each soil, was calculated from the Freundlich equation.

Sample No.:

#1

Type:

Koc

Value:

24 372 dimensionless

Temp.:

20 °C

Matrix:

Longwoods sandy loam

% Org. carbon:

1.3

Sample No.:

#2

Type:

Koc

Value:

8 751 dimensionless

Temp.:

20 °C

Matrix:

Farditch silt loam

% Org. carbon:

3.5

Sample No.:

#3

Type:

Koc

Value:

28 615 dimensionless

Temp.:

20 °C

Matrix:

Lockington clay loam

% Org. carbon:

2.8

Sample No.:

#4

Type:

Koc

Value:

29 418 dimensionless

Temp.:

20 °C

Matrix:

Clake sandy loam

% Org. carbon:

3.6

Sample No.:

#5

Type:

Koc

Value:

32 540 dimensionless

Temp.:

20 °C

Matrix:

South Witham clay loam

% Org. carbon:

3.8

Sample no.:

#1

Duration:

30 min

% Adsorption:

>= 71.9 - <= 84.7

Sample no.:

#2

Duration:

30 min

% Adsorption:

>= 90.8 - <= 92.9

Sample no.:

#3

Duration:

30 min

% Adsorption:

>= 91.5 - <= 93.6

Sample no.:

#4

Duration:

30 min

% Adsorption:

>= 89.1 - <= 91

Sample no.:

#5

Duration:

30 min

% Adsorption:

>= 92 - <= 93.1

Transformation products:

not measured

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Sample purity: The radiochemical purity of the test item in treatment solution was determined as 98.4% by HPLC. Comparison of mass spectroscopic data with that of a certified reference standard demonstrated that the test item was Bromoxynil Octanoate.
- Weighed soil: Approximately 5 g ode for each soil was weighed into pre-weighed PTFE tubes.
- Volume of CaCl2 solution: Calcium chloride solution (25 mL less the moisture content of the soil) was added.
- Test substance concentration in final solution: The definitive test was carried out at nominal concentrations of 0.05, 0.025, 0.0125, 0.005 and 0.00125 mg/L. Adsorption was performed by end-over-end shaking in the dark at 20°C for 30 minutes with no desorption phase due to instability of the test item.
- Other: The overall material balance for individual samples was in the range of 91.5-97.0% for the Longwoods sandy loam (mean 95.3%), 95.1- 104.4% for the Farditch silt loam (mean 99.3%), 92.0-104.9% for the Lockington clay loam (mean 97.5%), 97.2-106.4% for the Calke sandy loam (mean 100.0%) and 91.5-99.6% for the South Witham clay loam (mean 97.3%).

MAIN TEST: PERFORMANCE
- Test material stability during adsorption/desorption phase: Following HPLC-FC and TopCount™ analysis of the definitive samples, Bromoxynil Octanoate was found to be unstable in aqueous media while reasonable stability was indicated in soil extracts. Corrections were therefore made for the actual content of the test item in both phases. Due to analytical constraints, determinations had to be focused on duplicate samples at the highest test concentration. The averages of these duplicate analyses were applied through the concentration range.
- Experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): In the absence of soil, recovery of radioactivity from the tubes (treated at the 0.01 mg/L level) indicated adhesion to the vessel walls (mean recovery of 61.1% for the glass tubes and 54.6% for the PTFE tubes). Investigations were conducted to determine the extent of adsorption to the vessel in the presence of soil. Following the outcomes of these investigations and the benefit of higher centrifugation speeds permitted with their use, PTFE tubes were selected for the definitive phase of the study.

Validity criteria fulfilled:

not applicable

Reference 2

Endpoint:

adsorption / desorption: screening

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: Guidelines for Registering Pesticides in the United States, Subpart N, Chemistry Requirements: Environmental Fate, October 3, 1980. Environmental Protection Agency.

Version / remarks:

1980

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Analytical monitoring:

yes

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

5.6

% Silt:

17.6

% Sand:

76.8

% Org. carbon:

1.1

pH:

7.2

CEC:

6.5 meq/100 g soil d.w.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

>= 0.001 - <= 0.5 other: ppm

Sample No.:

#1

Type:

Kd

Value:

6.98 dimensionless

Matrix:

loamy sand

% Org. carbon:

1.1

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient of bromoxynil octanoate was determined. On sandy loam soil, the adsorption coefficient of bromoxynil octanoate was found to be k = 6.98.

Reference 3

Endpoint:

adsorption / desorption: screening

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 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Version / remarks:

1995

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 ± 2 °C

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

8

% Silt:

4

% Sand:

88

% Org. carbon:

0.5

pH:

7.6

CEC:

8.9 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

sandy loam

% Clay:

15

% Silt:

33

% Sand:

52

% Org. carbon:

2.2

pH:

7.4

CEC:

13.6 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

clay loam

% Clay:

34

% Silt:

28

% Sand:

38

% Org. carbon:

4.7

pH:

7.9

CEC:

26.6 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

sandy loam

% Clay:

13

% Silt:

12

% Sand:

75

% Org. carbon:

1.2

pH:

5.3

CEC:

6.1 meq/100 g soil d.w.

Validity criteria fulfilled:

not applicable

Conclusions:

In spite of the fact that this study was performed at a concentration above the nominal solubility of bromoxynil octanoate, it can be concluded that the compound was unstable in the presence of sterile soil and thus it was not possible to perform the definitive adsorption/desorption study under these conditions.

Reference 4

Endpoint:

adsorption / desorption: screening

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 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Version / remarks:

2000

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 ± 2 °C

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

8

% Silt:

4

% Sand:

88

% Org. carbon:

0.5

pH:

7.6

CEC:

8.9 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

sandy loam

% Clay:

13

% Silt:

32

% Sand:

55

% Org. carbon:

2.4

pH:

7.1

CEC:

22.6 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

clay

% Clay:

36

% Silt:

27

% Sand:

37

% Org. carbon:

3.8

pH:

8

CEC:

31.4 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

sandy loam

% Clay:

13

% Silt:

11

% Sand:

76

% Org. carbon:

1.1

pH:

5

CEC:

17.4 meq/100 g soil d.w.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

12.5 other: µg/L

Temp.:

20 °C

Sample No.:

#2

Duration:

24 h

Initial conc. measured:

12.5 other: µg/L

Temp.:

20 °C

Sample No.:

#3

Duration:

24 h

Initial conc. measured:

12.5 other: µg/L

Temp.:

20 °C

Sample No.:

#4

Duration:

24 h

Initial conc. measured:

12.5 other: µg/L

Temp.:

20 °C

Validity criteria fulfilled:

not applicable

Conclusions:

It was concluded that bromoxynil octanoate was not stable under the test conditions and, therefore, meaningful batch equilibrium sorption data cannot be obtained for this compound. Determination of the adsorption/desorption behaviour of bromoxynil octanoate (kinetics, isotherms) consequently could not be performed.

Reference 5

Endpoint:

adsorption / desorption: screening

Type of information:

(Q)SAR

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

Type of method:

other: The bromoxynil octanoate Koc soil adsorption coefficient was estimated based on the Sabljic molecular connectivity method with improved correction factors as implemented in the PCKOCWIN v1.66 model.

Type:

Koc

Value:

4 847 L/kg

Validity criteria fulfilled:

not applicable

Conclusions:

The bromoxynil octanoate Koc soil adsorption coefficient was estimated to be 4847 L/kg based on the Sabljic molecular connectivity method with improved correction factors as implemented in the PCKOCWIN v1.66 model.

Reference 6

Endpoint:

adsorption / desorption: screening

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 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

Version / remarks:

2001

GLP compliance:

yes (incl. QA statement)

Type of method:

HPLC estimation method

Details on study design: HPLC method:

Instrument:
HPLC System: Series 1100 chromatography workstation (Agilent):
- quaternary HPLC pump
- UV variable wavelength detector
- autosampler
- temperature controlled column compartment
- online vacuum solvent degasser
Software: Gina Star, Version 2.18 (Raytest)

Stationary Phase:
Chromatography Column: Hyperchrome Zorbax CN, 5 µm (Bischoff), length = 250 mm / inner diameter = 4.6 mm, Serial No.: 20094G015, Part No.: 2546D200ZX050
Guard Column: none used

Analytical Conditions:
Oven Temperature: 40 °C; Inject Volume: 50 µL
Flow Rate: 1.0 mL/min
Eluent: Methanol / 0.01 M Citrate buffer pH 6 (55 / 45 v/v, premixed)
Gradient Method: isocratic elution
Run Time: 30 min
UV Detection Wavelength: 220 nm

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient on soil (KOC) of the herbicide active substance Bromoxynil-Octanoate was estimated using the HPLC method according to OECD Test Guideline No. 121. The experiment was conducted in compliance with OECD-GLP standards. Eleven reference items for which reliable KOC values are known from the literature were chromatographed in duplicate on a cyanopropyl-type column. Sodium nitrate was used for determination of the chromatography system dead-time. Average capacity factors (k') were derived for each compound, and a linear calibration function was established for measured log k' values vs. literature log KOC values R2= (slope= 4.65, intercept = 1.03, 0.993). The capacity factor of the test item Bromoxynil-Octanoate was determined by replicate analysis within the same HPLC autosampler worklist as the reference items. Based on the above calibration equation, the soil adsorption coefficient of Bromoxynil-Octanoate was estimated as log KOC = 5.27, KOC = ca. 184300.
According to the BRIGGS classification system for the mobility of crop protection agents in soil based on their numeric adsorption coeffcients, Bromoxynil-Octanoate would be categorized as 'immobile'.

Reference 7

Endpoint:

adsorption / desorption: screening

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: Guidelines for Registering Pesticides In the United States, Subpart N, Chemistry Requirements: Evnironmental Fate, October 3, 1980. Environmental Protection Agency.

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

5.6

% Silt:

17.6

% Sand:

76.8

% Org. carbon:

1.1

pH:

7.2

CEC:

6.5 meq/100 g soil d.w.

Bulk density (g/cm³):

1.49

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

>= 0.005 - <= 0.5 other: ppm

Sample No.:

#1

Type:

Kd

Value:

6.98 dimensionless

Matrix:

loamy sand

% Org. carbon:

1.1

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficients of the bromoxynil octanoate was determined. On sandy loam soil, the compound was shown to have an adsorption coefficient of k =7.03.

Description of key information

log Koc = 3.94 – 4.51

Key value for chemical safety assessment

Koc at 20 °C:

8 751

Additional information

A key study assessed the adsorption of 2,6-dibromo-4-cyanophenyl octanoate in five different soils and followed GLP and OECD Guideline 106. The study found Freundlich adsorption constants related to the organic carbon content (Koc) ranging from 8751 to 32540 L/kg (log Koc = 3.94 – 4.51).

 

This result is supported by another study, according to GLP and OECD Guideline 121. Using High Performance Liquid Chromatography the Koc of the test substance was estimated to be 184300 (log Koc = 5.27).

 

In another study the Koc soil adsorption coefficient of the test substance was estimated to be 4847 L/kg based on the Sabljic molecular connectivity method with improved correction factors as implemented in the PCKOCWIN v1.66 model.

 

In two more studies the adsorption coefficient of 2,6-dibromo-4-cyanophenyl octanoate was determined on sandy loam soils. The adsorption coefficient of 2,6-dibromo-4-cyanophenyl octanoate was found to be k = 6.98 and k =7.03.

 

Two more studies are available, in which 2,6-dibromo-4-cyanophenyl octanoate was not stable under the test conditions and, therefore, meaningful batch equilibrium sorption data could be obtained for this compound. Determination of the adsorption/desorption behaviour of 2,6-dibromo-4-cyanophenyl octanoate (kinetics, isotherms) consequently could not be performed.

 

For the sake of completeness and to mention all available data, a position paper on the soil adsorption characteristics of the esters of bromoxynil is available. It and summarises and assesses the various attempts (all studies mentioned above) to obtain theoretical and experimental KOC values. It concluded that the recently conducted studies provide the most reliable results to date and that the mean KFOC value of 24739 mL/g for bromoxynil octanoate is a conservative values and is suitable for use in risk assessments.