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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
16 December 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
This study was performed according to OECD Guideline 121 with GLP statement.
Qualifier:
according to
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Deviations:
no
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil
Specific details on test material used for the study:
Test substance storage: protected from light
Stability at higher temperatures: Yes, maximum temperature: 40°C, maximum duration: 10 days
Volatile: Yes, vapour pressure: 1.51 Pa
Radiolabelling:
no
Test temperature:
35 ± 1 °C
Details on study design: HPLC method:
ANALYTICAL METHOD
- In this study an ultra performance liquid chromatography (UPLC) was used. The biggest difference between UPLC and HPLC is that UPLC works under much higher pressures and uses columns with smaller particles. This results in better resolution in shorter time frames.

EQUIPMENT
- HPLC method using soil-adsorption-reference data was applied for the determination of the adsorption coefficient (Koc) of test substance. To increase the resolution, UPLC was used instead of HPLC.
- Apparatus:
Instrument: Acquity UPLC system (Waters, Milford, MA, USA)
Detector: Acquity UPLC TUV detector (Waters)
Column: Acquity UPLC HSS Cyano, 100 mm × 2.1 mm i.d., dp = 1.8 μm (Waters)
Column temperature: 35°C ± 1°C
Mobile phase: 55/45 (v/v) methanol/water
Flow: 0.4 mL/min
Injection volume: 5 μL
UV detection: 210 nm

MOBILE PHASES
- Type: 55/45 (v/v) methanol/water

PREPARATION OF SOLUTIONS
All solutions containing the test substance were protected from light.
Solution of the unretained compound: A 5.0 g/L stock solution of formamide (99.2%, [75-12-7], Acros Organics, Geel, Belgium) in methanol was used. The stock solution was diluted to obtain an end solution of 55/45 (v/v) methanol/water.
The formamide blank solution was 55/45 (v/v) methanol/water.
Reference substance solutions: Stock solutions of the reference substances at concentrations of approximately 1 g/L in methanol were used. The stock solutions were diluted to obtain an end solution of 55/45 (v/v) methanol/water. The blank solution for the mixture of reference substances was 55/45 (v/v) methanol/water.
Test solution: A 1010 mg/L stock solution of the test substance was prepared in methanol. The stock solution was diluted to obtain an end solution of 55/45 (v/v) methanol/water. The final concentration of the test substance solution was 10.1 mg/L. The test substance blank solution was 55/45 (v/v) methanol/water.

REFERENCE SUBSTANCES
- Identity: See Table 5.4.1/1

DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column: 5 μL

REPETITIONS
- Number of determinations: The reference substance and test substance solutions were injected in duplicate. Blank solutions were analysed by single injection.

EVALUATION
- Calculation of capacity factors k': (tr-t0)/t0
- Calibration curve: logk' = alogkoc + b
tr = retention time (min)
t0 = dead time (min)
a = slope
b = intercept
Key result
Sample No.:
#1
Type:
Koc
Value:
820 dimensionless
pH:
7
Temp.:
35 °C
Matrix:
soil
Key result
Sample No.:
#1
Type:
log Koc
Value:
2.9 dimensionless
pH:
7
Temp.:
35 °C
Matrix:
soil
Details on results (HPLC method):
- Calculation of pKa values: No pKa values for acidic and basic groups in the molecular structure of the test substance in the logarithm range of 1 − 14 were calculated.
- Determination of the Koc: In the chromatogram of the test solution, one test substance peak was observed.
- Retention times of reference substances used for calibration: See table 5.4.1/2
- Details of fitted regression line (log k' vs. log Koc): The equation of the regression line was log k’ = 0.324 × log Koc – 0.853 (r = 0.98, n = 16).
- Graph of regression line attached: See "Attached background material" section
- Average retention data for test substance: 1.548

Table 5.4.1/2: Koc of the test substance

 

Substance

 

tr,1 [min]

 

tr,2 [min]

 

mean tr (n=2)

 

log Koc

 

Koc

 

Formamide (t0)

 

0.693

0.693

0.693

-

-

Acetanilide

 

0.903

0.902

-

1.26

-

Monuron

 

1.110

1.108

-

1.99

-

2,5-Dichloroaniline

 

1.260

1.258

-

2.55

-

Naphthalene

 

1.462

1.460

-

2.75

-

Benzoic acid phenylester

 

1.721

1.718

-

2.87

-

Fenthion

 

2.317

2.314

-

3.31

-

Phenanthrene

 

2.544

2.540

-

4.09

-

4,4’-DDT

 

6.338

6.339

-

5.63

-

Test substance – peak 1

 

1.548

1.547

1.548

2.92

8.2 x 102

Validity criteria fulfilled:
yes
Conclusions:
The HPLC method using soil-adsorption-reference data was applied for the determination of the adsorption coefficient (Koc) of test substance. To increase the resolution, UPLC was used instead of HPLC. The Koc and log Koc values of the test substance at neutral pH was: 820 and 2.9, respectively.
Executive summary:

The adsorption coefficient (Koc) for the test substance was determined according to OECD 121 guideline with GLP compliance. The HPLC method using soil-adsorption-reference data was applied for the determination of the adsorption coefficient (Koc) of test substance. To increase the resolution, UPLC was used instead of HPLC.

 

The column temperature of 35 ± 1 °C with a mobile phase consisting of 55 % methanol and 45 % water. A 10.1 mg/L sample of the test substance was analyzed using UPLC method. Solutions of reference substances with known log Koc values based on soil adsorption data and the test substance were analysed. Calibrations were performed using 8 reference items; retention times, capacity factors (k') and log k’ values of the references substances were plotted against the known log Koc values. Dead time of the UPLC-system was determined with Formamide. The retention times, capacity factor and log10 Koc value determined for the test substance at a constant UPLC column temperature of 35 ± 1 °C.

 

No pKa values for acidic and basic groups in the molecular structure of the test substance in the logarithm range of 1 − 14 were calculated. The equation of the regression line was: log k’ = 0.324 × log Koc – 0.853 (r = 0.98, n = 16).

 

The adsorption coefficient (Koc) and log Koc of the test substance at neutral pH was: 820 and 2.9, respectively.

Description of key information

OECD Guideline 121, EU Method C.19, GLP, key study, validity 1:

log Koc = 2.9 for soil

Koc = 820 for soil

The mobility of the substance in soils is considered as low (according to the criteria developed by P.J. McCall et al., 1981).

Key value for chemical safety assessment

Koc at 20 °C:
820

Additional information

To assess the adsorption potential of the registered substance on soil and on sewage sludge, one key study is available.

This study (WIL, 2015) was performed on the registered substance according to OECD Guideline 121 and EU Method C.19 (HPLC screening method) under GLP conditions. According to this study, the adsorption coefficient log Koc of the registered substance was determined at 2.9 for soil. The results indicate that the substance has low mobile in soils (according to P.J. McCall et al., 1981).

McCall P.J., Laskowski D.A., Swann R.L., and Dishburger H.J., (1981), “Measurement of sorption coefficients of organic chemicals and their use, in environmental fate analysis”, in Test Protocols for Environmental Fate and Movement of Toxicants. Proceedings of AOAC Symposium, AOAC, Washington DC.

Mobility classification scheme:

of Koc

Mobility class

0 - 50

Very high

50 - 150

High

150 - 500

Medium

500 - 2000

Low

2000 - 5000

Slightly

> 5000

Immobile

[LogKoc: 2.9]