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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from 23 May 2018 to 06 August 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Version / remarks:
2016
Deviations:
no
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
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil
Radiolabelling:
no
Test temperature:
Column temperature: 35°C ± 1°C
Details on study design: HPLC method:
UPLC CONDITIONS
- Instruments: Acquity UPLC system with TUV detector (Waters, USA)
- Column: Acquity UPLC HSS Cyano, 100 mm x 2.1 mm i.d., dp = 1.8 µm (Waters)
- Column temperature: 35°C ± 1°C
- Injection volume: 5 μL
- Flow: 0.4 mL/min
- UV detection: 210 nm

TESTS
Based on pKa values calculated for the substance, the HPLC method was performed at pH 7 and pH 9.

MOBILE PHASE
- Type: buffered mobile phase
- Composition: 55/45 (v/v) methanol/buffer pH 7 (Test at pH 7)
- Composition: 55/45 (v/v) methanol/buffer pH 9 (Test at pH 9)
- Buffer pH 7: Solution of 0.1 M potassium di-hydrogen-phosphate in water adjusted to pH 7 using 10N sodium hydroxide
- Buffer pH 9: Solution of 0.1 M boric acid in water and 0.1 M potassium chloride in water adjusted to pH 9 using 10N sodium hydroxide
- Type of water: Tap water purified by a Milli-Q water purification system (Millipore, USA)

DETERMINATION OF DEAD TIME
- Method: by inert substance which is not retained by the column. Formamide was used in this study.
- A solution of formamide was prepared in 75/25 (v/v) methanol/buffer pH 7 from a 5 g/L stock solution in methanol.
- A solution of formamide was prepared in 75/25 (v/v) methanol/buffer pH 9 from a 5 g/L stock solution in methanol.

REFERENCE SUBSTANES
- Identity: Acetanilide, Monuron, 2,5-Dichloroaniline, Naphthalene, Benzoic acid phenylester, Fenthion, Phenanthrene and 4,4’-DDT.
- The log Koc values of the reference substances are as mentioned in OECD TG121 (based on soil adsorption data).
- Stock solutions (1 g/L) of the reference substances in methanol (or acetonitrile) were diluted to obtain an end solution of 75/25 (v/v) methanol/buffer pH 7.
- Stock solutions (1 g/L) of the reference substances in methanol (or acetonitrile) were diluted to obtain an end solution of 75/25 (v/v) methanol/buffer pH 9.

TEST ITEM
- A 10.0 mg/L test item solution was prepared in 75/25 (v/v) methanol/buffer pH 7 from a stock solution (1 g/L) in methanol.
- A 10.0 mg/L test item solution was prepared in 75/25 (v/v) methanol/buffer pH 9 from a stock solution (1 g/L) in methanol.

DETERMINATION OF RETENTION TIMES
- Duplicate injections of the unretained substance, reference substances and test item.
- Single injection of the blank (75/25 (v/v) methanol/buffer pH 7 or 75/25 (v/v) methanol/buffer pH 9).

DATA HANDLING
- Dead time (t0) = mean retention time of the unretained substance
- Calculation of capacity factor k' of each compound from its retention time : k' = (tr-t0)/t0
- Log k’ values (references substances) were plotted against their known log Koc values using linear regression analysis (least squares method).
- Log Koc of the substance was calculated by substituting its mean log k’ in the regression line (log k' vs log Koc).
Key result
Type:
log Koc
Value:
5.19 dimensionless
pH:
7
Temp.:
20 °C
Remarks on result:
other: Peak area of 99%
Key result
Type:
log Koc
Value:
5.06 dimensionless
pH:
9
Temp.:
20 °C
Remarks on result:
other: Peak area of 98%
Details on results (HPLC method):
Test at pH 7
- Retention times of reference substances used for calibration: see table below
- Details of fitted regression line: log k’ = 0.323 log Koc– 0.774 (r=0.98, n=16)
- The chromatogram of test item showed one major peak (99%) and two small peaks (<1%).
- The log Koc for the major peak was reported as the log Koc of the substance.
- Average retention data for the test item: see table below
- The value of log Koc obtained from duplicate measurements was within ± 0.25 log units.

Test at pH 9
- Retention times of reference substances used for calibration: see table below
- Details of fitted regression line: log k’ = 0.297 log Koc– 0.868 (r=0.97, n=16)
- Regression line: see illustration below
- The chromatogram of test item showed one major peak (98%) and two small peaks (<1% and 1.4%).
- The log Koc for the major peak was reported as the log Koc of the substance.
- Average retention data for the test item: see table below
- The value of log Koc obtained from duplicate measurements was within ± 0.25 log units.

Table: Results Adsorption coefficient (HPLC estimation method) - pH 7

Substance

Retention time (min)

log Koc

Koc

Peak area
(%)

RT1

RT2

mean

Formamide (t0)

0.695

0.694

0.695

 

 

 

Acetanilide

0.943

0.938

0.941

1.26

 

 

Monuron

1.193

1.182

1.188

1.99

 

 

2,5-Dichloroaniline

1.374

1.359

1.367

2.55

 

 

Naphthalene

1.635

1.614

1.625

2.75

 

 

Benzoic acid phenylester

1.987

1.952

1.970

2.87

 

 

Fenthion

2.656

2.598

2.627

3.31

 

 

Phenanthrene

2.974

2.903

2.939

4.09

 

 

4,4’-DDT

7.406

7.146

7.276

5.63

 

 

Test item – peak 1

3.177

3.167

3.172

4.11

1.3E4

0.21

Test item – peak 2

6.241

6.213

6.227

5.19

1.5E5

99

Test item – peak 3

6.971

6.947

6.959

5.35

2.3E5

0.57

 

Table: Results Adsorption coefficient (HPLC estimation method) - pH 9

Substance

Retention time (min)

log Koc

Koc

Peak area
(%)

RT1

RT2

mean

Formamide (t0)

0.718

0.717

0.718

 

 

 

Acetanilide

0.901

0.903

0.902

1.26

 

 

Monuron

1.073

1.079

1.076

1.99

 

 

2,5-Dichloroaniline

1.212

1.215

1.214

2.55

 

 

Naphthalene

1.399

1.400

1.400

2.75

 

 

Benzoic acid phenylester

1.599

1.610

1.605

2.87

 

 

Fenthion

1.991

1.997

1.994

3.31

 

 

Phenanthrene

2.217

2.233

2.225

4.09

 

 

4,4’-DDT

4.476

4.579

4.528

5.63

 

 

Test item – peak 1

2.265

2.277

2.271

4.05

1.1E4

0.17

Test item – peak 2

3.803

3.816

3.810

5.06

1.1E5

98

Test item – peak 3

4.187

4.212

4.200

5.23

1.7E5

1.4

 

Conclusions:
The log Koc of the substance at pH 7 and ca. 20°C was determined to be 5.19. Koc= 1.5E05.
The log Koc at pH 7 and ca. 20°C for the impurities was determined to be 4.11 and 5.35. Koc= 1.3E4 and 2.3E05, resp.

The log Koc of the substance at pH 9 and ca. 20°C was determined to be 5.06. Koc= 1.1E05.
The log Koc at pH 9 and ca. 20°C for the impurities was determined to be 4.05 and 5.23. Koc= 1.1E4 and 1.7E05, resp.
Executive summary:

The adsorption coefficient (Koc) of the substance was determined using the HPLC estimation method based on soil-adsorption reference data. The study was performed in accordance with EC C.19 and OECD 121 and in compliance with GLP. Formamide was used as unretained substance. For the construction of the regression line, eight references substances (with log Koc range according to OECD TG121: 1.26 to 5.63 at ca. 20°C) were used. Duplicate injections of unretained substance, reference substances and test item in an UPLC-UV system. Based on pKa values calculated for the substance, the HPLC method was performed at pH 7 and pH 9. Mobile phase was 55/45 (v/v) methanol/buffer pH 7 or 55/45 (v/v) methanol/buffer pH 9. The wavelength of detection was 210 nm. The stationary phase contained cyanopropyl chains chemically bonded to silica. Each chromatogram of the substance showed one major peak and two smaller peaks. Substituting the mean retention times in the regression line yielded the (log) Koc values as presented in the table below:

 

pH 7

pH 9

Koc

log Koc

Peak area
(%)

Koc

log Koc

Peak area
(%)

Test item – peak 1

1.3E4

4.11

0.21

1.1E4

4.05

0.17

Test item – peak 2

1.5E5

5.19

99

1.1E5

5.06

98

Test item – peak 3

2.3E5

5.35

0.57

1.7E5

5.23

1.4

Description of key information

Koc at 20°C: 1.1E05 (EC C.19, OECD 121: HPLC estimation method based on soil-adsorption reference data)

Key value for chemical safety assessment

Koc at 20 °C:
110 000

Additional information

Log Koc of the main peak (99%) at pH 7: 5.19, Koc: 1.5E05

Log Koc of the main peak (99%) at pH 9: 5.06, Koc: 1.1E05

For the derivation of PNECsed and PNECsoil values, the lowest Koc of 1.1E05 is used, as this is considered worst case for sediment and soil.