2,6-dibromo-4-cyanophenyl heptanoate

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

Study period:

11 Nov 2011 - 24 Jul 2013

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: Regulation (EC) No 1107/2009 of the European Parliament and of the Council of 21 October 2009 concerning the placing of plant protection products on the market and repealing Council Directives 79/117/EEC and 91/414/EEC

Version / remarks:

2009

Qualifier:

according to guideline

Guideline:

other: US EPA, Pesticide Assessment Guidelines, Subdivision N, Environmental Fate, § 163-1: Leaching and Adsorption/desorption Studies.

Version / remarks:

1982

Qualifier:

according to guideline

Guideline:

other: Canada Pest management Regulatory Agency (PMRA), Environmental Chemistry and Fate, Guidelines for Registration of Pesticides in Canada.

Version / remarks:

1987

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 ± 2 °C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: The target nominal concentrations were 0.1, 0.05, 0.01, 0.005 and 0.001 mg/L [14C]-Bromoxynil Heptanoate.
- Sampling interval: Adsorption time was reduced to the minimum allowable by the guideline (i.e. 30 minutes) and due to the limited stability of the test item, no desorption step was conducted.

Matrix no.:

#1

Matrix type:

other: Sandy loam; soil identification: Longwoods

% 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: Silt loam; soil identification: Farditch

% Clay:

17

% Silt:

56

% Sand:

27

% 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: Clay loam; soil identification: Lockington

% 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: Sandy loam; soil identification: Calke

% 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: Clay loam; soil identification: South Witham

% 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.
- 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: Soils were stored, in the dark, at a temperature of ca 4 °C.
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): 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.
Longwoods: Dried and sieved to 2 mm
Farditch Farm: Dried slightly and sieved to 2 mm
Lockington: Air dried and sieved to 2 mm
Calke: Sieved to 2 mm
South Witham: Dried slightly and sieved to 2 mm

PROPERTIES
- For information on soil properties see Table “Matrix properties”

Details on test conditions:

- Duplicate tubes for each concentration and each soil were prepared at the 1:5 soil to solution ratio. PTFE tubes were used and hence the maximum centrifuge speed of 3,400 rpm was adopted. Adsorption time was reduced to the minimum allowable by the guideline (i.e. 30 minutes) and due to the limited stability of the test item, no desorption step was conducted.
- The target nominal concentrations were 0.1, 0.05, 0.01, 0.005 and 0.001 mg/L [14C]-Bromoxynil Heptanoate.
- 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.
- The soil solutions were mixed and slurried for approximately 30 minutes on an end-over-end shaker in the dark at a temperature of 20 ± 2 °C.

Sample No.:

#1

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.1 other: mg/L

Temp.:

20 °C

Remarks:

Soil identification: Longwoods

Sample No.:

#2

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.1 other: mg/L

Temp.:

20 °C

Remarks:

Soil identification: Farditch

Sample No.:

#3

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.1 other: mg/L

Temp.:

20 °C

Remarks:

Soil identification: Lockington

Sample No.:

#4

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.1 other: mg/L

Temp.:

20 °C

Remarks:

Soil identification: Calke

Sample No.:

#5

Duration:

30 min

Initial conc. measured:

>= 0.001 - <= 0.1 other: mg/L

Temp.:

20 °C

Remarks:

Soil identification: South Witham

Sample No.:

#1

Type:

Koc

Value:

51 659 L/kg

Temp.:

20 °C

Matrix:

#1; soil identification: Longwoods

% Org. carbon:

1.3

Sample No.:

#2

Type:

Koc

Value:

12 835 L/kg

Temp.:

20 °C

Matrix:

#2; soil identification: Farditch

% Org. carbon:

3.45

Sample No.:

#3

Type:

Koc

Value:

47 260 L/kg

Temp.:

20 °C

Matrix:

#3; soil identification: Lockington

% Org. carbon:

2.76

Sample No.:

#4

Type:

Koc

Value:

17 119 L/kg

Temp.:

20 °C

Matrix:

#4; soil identification: Calke

% Org. carbon:

3.56

Sample No.:

#5

Type:

Koc

Value:

11 191 L/kg

Temp.:

20 °C

Matrix:

#5; soil identification: South Witham

% Org. carbon:

3.8

Sample no.:

#1

Duration:

30 min

% Adsorption:

>= 60.4 - <= 65.1

Remarks on result:

other:

Remarks:

Soil identification: Longwoods

Sample no.:

#2

Duration:

30 min

% Adsorption:

>= 90.9 - <= 93.5

Remarks on result:

other:

Remarks:

Soil identification: Farditch

Sample no.:

#3

Duration:

30 min

% Adsorption:

>= 90.5 - <= 93.2

Remarks on result:

other:

Remarks:

Soil identification: Lockington

Sample no.:

#4

Duration:

30 min

% Adsorption:

>= 86.9 - <= 91.9

Remarks on result:

other:

Remarks:

Soil identification: Calke

Sample no.:

#5

Duration:

30 min

% Adsorption:

>= 90.6 - <= 93.5

Remarks on result:

other:

Remarks:

Soil identification: South Witham

Transformation products:

not specified

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Sample purity: The radiochemical purity of the test item in treatment solution was determined as 99.1% by HPLC. Comparison of mass spectroscopic data with that of a certified reference standard demonstrated that the test item was Bromoxynil Heptanoate.

MAIN TEST: PERFORMANCE
- Test material stability during adsorption/desorption phase: Following HPLC-FC and TopCount™ analysis of the definitive samples, Bromoxynil Heptanoate was found to be unstable in aqueous media while limited 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. The test systems were maintained in the dark and at a temperature of 20 ± 2°C throughout the study. The pH of the calcium chloride solutions used during this study was found to be in the range 6.1 to 6.2.

RESIDUES
- Total recovery: The recovery of radioactivity was quantitative, with all recoveries within the range of 90-110% of applied radioactivity, with a single exception (Lockington clay loam with a recovery of 111.9% at the lowest concentration). The overall material balance for individual samples was in the range of 97.9-103.6% for the Longwoods sandy loam (mean 99.6%), 96.8-107.8% for the Farditch silt loam (mean 101.3%), 97.6-111.9% for the Lockington sandy loam (mean 101.4%), 97.0-109.6% for the Calke sandy loam (mean 101.3%) and 94.4-107.6% for the South Witham clay loam (mean 99.7%).
- For all soils the fit of log Cs1 vs. log Cw1 to a linear equation, was good with correlation coefficients ranging from 0.995 (Calke sandy loam and South Witham clay loam soils) to 0.998 (Longwoods sandy loam ), with a mean of 0.996 for all soils.
- There was a near-linear relationship between the soil and solution concentration for all soils tested, with 1/n values ranging from 0.95 in the Farditch silt loam to 1.06 in the Lockington sandy loam.
- The Kf values (corrected for the actual amount of test item detected in each phase) ranged from 425 mL/g in the South Witham clay loam to 1304 mL/g in the Lockington sandy loam (mean of 691 mL/g). Corresponding values for Koc ranged from 11191 mL/g in the South Witham clay loam to 51659 mL/g in the Longwoods sandy loam, with a mean value of 28013 mL/g.

Validity criteria fulfilled:

not applicable

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

06 Aug 2009 - 24 Nov 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

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

Radiolabelling:

no

Test temperature:

25 °C

Sample No.:

#1

Type:

log Koc

Value:

4.2 dimensionless

Temp.:

25 °C

Remarks on result:

other:

Remarks:

log Koc determined by HPLC method

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient (KOC) of Bromoxynil heptanoate was determined according to the OECD guideline 121 and the guideline 2001/59/EEC C.19. Nine calibration substances were injected into an HPLC-system under the same analytical conditions (column temperature 25°C) as for the test item (repeat determination). Calibration curves were created by using the measured retention times (log k’-values) and the known log KOC-values of the calibration substances for linear regression.
The adsorption coefficient (KOC) of Bromoxynil heptanoate was determined at 25 °C as 16000 (log Koc = 4.2).

Description of key information

log Koc = 4.05 – 4.71

Key value for chemical safety assessment

Koc at 20 °C:

11 191

Additional information

The Freundlich adsorption constant of radiolabelled 2,6-dibromo-4-cyanophenyl heptanoate related to organic carbon content (Koc) was tested in a study following GLP and OECD Guideline 106. The study was conducted using five different soils (2x sandy loam, silt loam, 2x clay loam). The Koc of the test substance ranged from 11191 to 51659 L/kg (log Koc = 4.05 – 4.71).

 

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 4.2.

 

For the sake of completeness and to mention all available data, a position paper on the soil adsorption characteristics of the esters of 3,5-dibromo-4-hydroxybenzonitrile (CAS 1689-84-5) is available. It and summarises and assesses the various attempts 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 28013 mL/g for 2,6-dibromo-4-cyanophenyl heptanoate is a conservative values and is suitable for use in risk assessments.