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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
19 July 2016 to 16 March 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same 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))
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
GLP compliance:
yes (incl. QA statement)
Type of method:
HPLC estimation method
Media:
soil
Radiolabelling:
no
Test temperature:
The column temperature was 25 °C.
Details on study design: HPLC method:
METHOD
The sorption behaviour of the test material on soil can be investigated using high performance liquid chromatography (HPLC). This is performed on commercially available analytical columns packed with a solid phase containing a moderately polar stationary phase with lipophilic and polar moieties (e.g. cyano-propyl bonded phase). The chemicals injected onto the column move along it by partitioning between the mobile phase and the stationary phase. The velocity of each component thereby depends on the degree of adsorption on the stationary phase. The dual nature of the stationary phase allows for interaction of polar and apolar parts of a molecule in a similar way as is the case for soil. This enables the relationship between the retention time on such a column and the adsorption coefficient on the organic parts of the soil to be established.
The adsorption coefficient is deduced from the capacity factor (k’) given by:
k' = (tr - to) / to
where:
tr is the measured retention time of sample or reference
to is the retention time of the internal deadtime standard (I.D.S)

PROCEDURE
In order to correlate the measured capacity factor (k’) of the test material with its Koc, six reference materials were selected from a list of recommended compounds. These reference compounds were selected to have log10 Koc values between 1.3 and 5.6. An internal standard (formamide) with no retention on the HPLC column was used to determine the deadtime of the HPLC system.
A solution of test material (approximately 16 mg/L in HPLC mobile phase, and also containing I.D.S.) was prepared and chromatographed in duplicate, bracketed by samples of the reference mixture, using the following HPLC conditions:
Instrument: Agilent 1200 Series Liquid Chromatograph with Chemstation software
Column: HyperClone CN (CPS), 5 μm (25 cm x 4.6 mm internal diameter)
Column temperature: 25 °C
Mobile phase composition: Acetonitrile:pH 7 phosphate buffer (55:45 v/v)
Flow rate: 1.0 mL/minute
Injection volume: 20 μL
Detector: UV set at 210 nm
Key result
Type:
log Koc
Value:
2.8 dimensionless
Temp.:
25 °C
Matrix:
Soil (HPLC)
Key result
Type:
Koc
Value:
560 dimensionless
Temp.:
25 °C
Matrix:
Soil (HPLC)
Details on results (HPLC method):
A calibration plot of log10 k’ versus log10 Koc was constructed for the reference standards and the logarithm of the capacity factor for the test material was then calculated and the log10Koc value was determined by interpolation.

Table 2: HPLC Determination of Log10 Koc for the test material

Sample

Component

tr (minutes)

k’

log10 k’

log10 Koc

 

Standard Run A (t0 = 2.683 minutes)

Acetanilide

3.349

0.248

-0.605

1.3

Nitrobenzene

4.235

0.578

-0.238

2.4

Naphthalene

4.936

0.840

-0.076

2.8

2-Methylnaphthalene

5.238

0.952

-0.021

3.9

Anthracene

5.826

1.171

0.069

4.4

DDT

8.773

2.270

0.356

5.6

Sample A (t0 = 2.680 minutes)

Test material

4.297

0.603

-0.219

2.8

Sample B (t0 = 2.678 minutes)

Test material

4.295

0.604

-0.219

2.8

 

Standard Run B (t0 = 2.678 minutes)

Acetanilide

3.344

0.249

-0.604

1.3

Nitrobenzene

4.229

0.579

-0.237

2.4

Naphthalene

4.929

0.841

-0.075

2.8

2-Methylnaphthalene

5.231

0.953

-0.021

3.9

Anthracene

5.819

1.173

0.069

4.4

DDT

8.760

2.271

0.356

5.6

Linear regression (based on mean of standard runs A and B): log10 Koc = 4.73 log10 k’ + 3.78

Validity criteria fulfilled:
not applicable
Conclusions:
Under the conditions of this study, the test material was determined to have a log10 Koc value of 2.8 (equivalent to a Koc value of 560).
Executive summary:

The soil adsorption potential of the test material was estimated in accordance with the standardised guidelines OECD 121 and EU Method C.19 under GLP conditions using the HPLC Method.

HPLC was performed on commercially available analytical columns packed with a solid phase containing a moderately polar stationary phase with lipophilic and polar moieties. The adsorption coefficient is deduced from the capacity factor (k’). A solution of test material (approximately 16 mg/L in HPLC mobile phase, and also containing internal deadtime standard) was prepared and chromatographed in duplicate, bracketed by samples of the reference mixture. A calibration plot of log10 k’ versus log10 Koc was constructed for the reference standards. The logarithm of the capacity factor for the test material was then calculated and the log10 Koc value was determined by interpolation.

Under the conditions of this study, the test material was determined to have a log10 Koc value of 2.8 (equivalent to a Koc value of 560).

Description of key information

Under the conditions of this study, the test material was determined to have a log10 Koc value of 2.8 (equivalent to a Koc value of 560).

Key value for chemical safety assessment

Koc at 20 °C:
560

Additional information

The soil adsorption of the test material was estimated in accordance with the standardised guidelines OECD 121 and EU Method C.19 under GLP conditions using the HPLC Method. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

HPLC was performed on commercially available analytical columns packed with a solid phase containing a moderately polar stationary phase with lipophilic and polar moieties. The adsorption coefficient is deduced from the capacity factor (k’). A solution of test material (approximately 16 mg/L in HPLC mobile phase, and also containing internal deadtime standard) was prepared and chromatographed in duplicate, bracketed by samples of the reference mixture. A calibration plot of log10 k’ versus log10 Koc was constructed for the reference standards. The logarithm of the capacity factor for the test material was then calculated and the log10 Koc value was determined by interpolation.

Under the conditions of this study, the test material was determined to have a log10 Koc value of 2.8 (equivalent to a Koc value of 560).

[LogKoc: 2.8]