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Adsorption / desorption

Link to relevant study record(s)

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

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

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 10^2

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]