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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:
17 August 2009 to 22 August 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))
Deviations:
no
GLP compliance:
yes
Remarks:
Date of GLP inspection: 19-08-09 Date of signature: 04/03/09
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Test temperature:
The HPLC analyses were performed on the test and reference substances with the column maintained at constant temperature of 30°C. Because the experimentally-derived Koc values of the reference substances were determined at a temperature of 20-25°C (per OECD 106), the derived estimates of Koc for the test substance should also relate to a temperature range of 20-25°C.
Details on study design: HPLC method:
Preparation of sample solution - Test material (0.1044 g) was diluted to 100 mL with methanol.
Preparation of dead time solution - The dead time was determined by measuring the retention time of formamide (purity* ≥99.5%, 554 mg/L solution in mobile phase).
Preparation of reference standard solutions - Solutions of reference standards (please see table 4.1 in section “any other information on materials and methods including tables”) were prepared in methanol.

Determination of retention time - The sample, dead time and reference standard solutions were injected in duplicate using the following HPLC parameters:
HPLC System: Agilent Technologies 1100, incorporating autosampler and workstation
Column: Optimal CN 5 µ (150 x 4.6 mm id)
Column temperature: 30ºC
Mobile phase: methanol : water (55 : 45 v/v)
pH of mobile phase: 6.7
Flow-rate: 1.0 mL/min
Injection volume: 10 µL
UV detector wavelength :dead time and reference standards: 210 nm sample: 310 nm

Construction of calibration curve - A calibration curve was constructed from the retention time data of the dead time and reference standard solutions (please see attached Figure 4.1). The capacity factors (k) for the reference standards were calculated using Equation 4.1.
Adsorption coefficient of sample - The capacity factor was calculated using Equation 4.1 and the log10 Koc value determined using Equation 4.2 with reference to the calibration curve (Figure 4.1).

Calculation
Capacity factor - The capacity factor was determined using Equation:

k = (tr-t0) / t0
where:
k = capacity factor
tr = retention time (min)
t0 = dead time (min)

Adsorption Coefficient - The adsorption coefficient was calculated using Equation:
log10 Koc = (log10k - A) / B
where:
Koc = adsorption coefficient
k = capacity factor
A = intercept of the calibration curve (Figure 4.1)
B = slope of the calibration curve (Figure 4.1)
Analytical monitoring:
no
Details on sampling:
Determination of Koc for the test substance was based on duplicate analyses.
Details on test conditions:
Reference substances were prepared in methanol at approximately 100 mg/L. Test substance was dissolved in methanol at 1000 mg/L.
Computational methods:
Linear regression of log k' versus log Koc for reference substances, giving the regression equation:
log k' = 0.337*log Koc - 0.766
Type:
Koc
Value:
933
Type:
log Koc
Value:
2.97
Details on results (HPLC method):
The test material comprises four main components (refer to Characterisation GC-MS, Harlan Laboratories Ltd project number 0044/1444). From the chromatography it was evident that no separation occurred and that the components co-eluted. This observation is consistent with the equivalent predicted values of log10Koc for 1,3- and 1,4-ethylvinylbenzene and 1,3- and 1,4-divinylbenzene (log10Koc 3.14) obtained using the computer based estimation software KOCWIN v2.00 (February 2008) ©2000-2008 U.S. Environmental Protection Agency. The estimated Koc value falls within a factor of two of the reported HPLC derived value and supports the assignment of a single value of adsorption coefficient to all main components of the test material.

See Remarks on Results section for results tables
Transformation products:
not measured

Calibration

The retention times of formamide and the retention times, capacity factors (k) and log10Koc values for the reference standards are shown in the two following tables:

Table 4.2

Dead Time

Retention Time (mins)

Mean Retention Time (mins)

Injection 1

Injection 2

Formamide

1.944

1.945

1.945

Table 4.3

Standard

Retention Time (mins)

Mean Retention Time (mins)

Capacity Factor (k)

Log10k

Log10Koc

Injection 1

Injection 2

Acetanilide

2.584

2.584

2.584

0.329

-0.483

1.25

Phenol

2.722

2.722

2.722

0.400

-0.398

1.32

Atrazine

3.081

3.082

3.082

0.585

-0.233

1.81

Isoproturon

3.379

3.376

3.378

0.737

-0.133

1.86

Triadimenol

4.250

4.246

4.248

1.19

7.36 x 10-2

2.40

Linuron

5.313

5.315

5.314

1.73

0.239

2.59

Naphthalene

4.730

4.734

4.732

1.43

0.156

2.75

Endosulfan-diol

7.064

7.059

7.062

2.63

0.420

3.02

Fenthion

8.729

8.724

8.727

3.49

0.543

3.31

a-Endosulfan

10.293

10.295

10.294

4.29

0.633

4.09

Phenanthrene

8.336

8.334

8.335

3.29

0.517

4.09

Diclofop-methyl

10.144

10.134

10.139

4.21

0.625

4.20

DDT

21.662

21.681

21.672

10.1

1.01

5.63

 

Please see attached Fig 4.1 Calibration Curve


Adsorption coefficient of sample

The retention times, capacity factors and log10Koc values determined for the sample are shown in the following table:

Table 4.4

Injection

Retention Time (mins)

Capacity Factor (k)

Log10k

Log10Koc

1

5.287

1.72

0.235

2.97

2

5.291

1.72

0.236

2.97

Mean log10Koc:                               2.97
Adsorption coefficient (Koc):          933

Validation of Results

Duplicate determinations of log10Koc were within acceptable limits of 0.25 log unit.

For the column used the following criteria were reached; log k > 0.0 for log10Koc 3.0 and log k > -0.4 for log10Koc2.0.

The results have been considered to fully meet the OECD criteria for the validity of this test with respect to repeatability and anticipated log k values.

Validity criteria fulfilled:
yes
Conclusions:
The adsorption coefficient (Koc) of the test material has been determined to be 933, log10 Koc = 2.97.
Executive summary:

The test material and reference substances were dissolved in methanol, although the guideline states that these should be dissolved in mobile phase. However, some reference substances are not readily soluble in mobile phase at the concentrations required for analysis. Additionally, since both the test material and the reference substances were dissolved in the same solvent, the effect on the relative capacity factors was not considered to be significant. The dead time sample was prepared in mobile phase since interference at the dead volume can be observed should this be prepared in pure methanol. The test material comprises four main components (refer to Characterisation GC-MS, Harlan Laboratories Ltd project number 0044/1444). From the chromatography it was evident that no separation occurred and that the components co-eluted. This observation is consistent with the equivalent predicted values of log10Koc for 1,3- and 1,4-ethylvinylbenzene and 1,3- and 1,4-divinylbenzene (log10Koc 3.14) obtained using the computer based estimation software KOCWIN v2.00 (February 2008) ©2000-2008 U.S. Environmental Protection Agency. The estimated Koc value falls within a factor of two of the reported HPLC derived value and supports the assignment of a single value of adsorption coefficient to all main components of the test material. The adsorption coefficient (Koc) of the test material has been determined to be 933, log10Koc  = 2.97.

Description of key information

Log Koc = 2.97, representing a composite estimate (HPLC) value for the structurally similar components of DVB-55 and DVB-HP.

Key value for chemical safety assessment

Koc at 20 °C:
933

Additional information

The method guideline states that the measurement of adsorption coefficient should be carried out on substances in their ionised and unionised forms. However, the test material does not contain any modes of dissociation; therefore, testing was performed at approximately neutral pH, with the test material in an unionised form. The test material comprises four main components. From the chromatography it was evident that no separation occurred and that the components co-eluted. This observation is consistent with the equivalent predicted values of log Koc for 1,3- and 1,4-ethylvinylbenzene and 1,3- and 1,4-divinylbenzene (log Koc = 3.14) obtained using the computer-based estimation software KOCWIN v2.00 (February 2008) ©2000-2008 U.S. Environmental Protection Agency. The estimated Koc value falls within a factor of two of the reported HPLC-derived value and supports the assignment of a single value of adsorption coefficient to all main components of the test material.