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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:
2017-10-05 to 2017-12-04
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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))
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No. of test material: Vinylcyclohexane (Hydrotox: #17/5598; VUOS: VCH/7/17K1)

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Fridge at 5°C ± 3°C
Radiolabelling:
no
Test temperature:
HPLC conditions:
Temperature 40°C
Autosampler temperature 25°C
Details on study design: HPLC method:
EQUIPMENT
- Apparatus: HPLC system Shimadzu LC 2010 (HPLC 11; lD 381) series with an UV-Vis-detector and for the chromatographical separation a Nucleosil 100 CN-column (250x4.6 mm, 5 pm) from Macherey-Nagel were used.
- Chemicals and Reagents: Water, HPLC Grade (18.2 pQ cm'1, Nanopure Diamond); Methanol, HPLC analyzed (J.T. Baker)
- HPLC-Conditions:
Mobile phase = Methanol / HPLC-water (40:60% v/v)
Column = Nucleosil 100 CN, 250x4.6 mm, 5pm
Flow rate = 1.0 mL/min
Temperature = 40 °C
Autosampler temperature = 25°C
Detector = 200 nm
Injection = 20 µl
Runtime = 10 min

DETERMINATION OF DEAD TIME
- Method: The dead time for the calculation was determined with urea

REFERENCE SUBSTANCES
- Identity: Due to the structural differentiation between test item and the reference substances listed in the OECD Guideline 121, six structurally heterogeneous substances were used for the study. The reference substances were prepared by weighing 15 mg of each reference substance in a separated 100 mL volume flask and dissolving in methanol. Accordingly, a 1:50 dilution of each stock solution was prepared with mobile phase.
Reference substances, batch/supplier, and nominal concentration:
> Urea, SZBEO650V/ Sigma Aldrich, 0.003 mg/mL
> Acetanilide, A033682 / Acros, 0.003 mg/mL
> N,N‘-Dimethylbenzamide, L2COP748 / J&K Scientific, 0.003 mg/mL
> lsoproturon, SZBD221XV / Sigma Aldrich, 0.003 mg/mL
> Linuron, BCBSS112V/ Sigma Aldrich, 0.003 mg/mL
> Naphthalene, 137241515 / Roth, 0.003 mg/mL
> Fenthion, BCBT4329 / Sigma Aldrich, 0.003 mg/mL

- Sample Preparation: The test item was prepared by weighing of 200 mg in a 20-mL volume flask, dissolving in methanol and a 1:20 dilution with mobile phase.
- Data Handling: All chromatographic data were collected by using LabSolutions chromatographic software, which enables conformity to 21 CFR Part 11 guidelines. The method and the sequence file were constructed and downloaded prior to the injection of the first sample. The capacity factors were calculated by the formula given in OECD Guideline 121. For calculation of the log Koc value of the test item a calibration curve of the logarithms of the adsorption coefficients over the logarithms of capacity factors of the reference substances was plotted and the linear regression (R220.95) assigned. The calculation of the sample adsorption coefficients was performed using Excel. The results for the adsorption coefficients of vinylcyclohexane are given with two decimal places.
The determinations should be run at least in duplicate. The values of log Koc derived from individual measurements should be within a range 0f 0.25 log unit. Reference substances may be injected as a mixed standard to determine their retention times, provided it has been confirmed that the retention time of each reference standard is unaffected by the presence of the other reference standards.

REPETITIONS
- Number of determinations: 2

EVALUATION
- Calculation of capacity factors k': The capacity factor k‘ was calculated by the formula given in OECD Guideline 121:
k’ =(tR —t0) / t0
k’ = capacity factor
tR = HPLC retention time of test and reference substance (minutes)
t0 = HPLC dead time (minutes)

- Determination of the log Koc value: For calculation of the log Koc value of the test item a calibration curve of the logarithms of the adsorption coefficients over the logarithms of capacity factors of the reference substances was plotted and the linear regression (R2 ≥ 0.95) was assigned.
From this follows:
log Koc = a * log k’+b

b = slope of the calibration curve
a = intercept with the axis
log KOC = logarithm of adsorption coefficient
Key result
Type:
log Koc
Value:
2.29 dimensionless
Matrix:
soil
Key result
Type:
log Koc
Value:
2.55 dimensionless
Matrix:
Sewage sludge
Details on results (HPLC method):
- Retention times of reference substances used for calibration:
[substance: first measurement, second measurement]
Urea (dead time): 3.41 min, 3.40 min
Acetanilide: 4.19 min, 4.19 min
N,N'-Dimethylbenzamide: 4.38 min, 4.38 min
Isoproturon: 5.21 min, 5.21 min
Linuron: 5.71 min, 5.71 min
Naphthalene: 5.98 min, 5.98 min
Fenthion: 7.53 min, 7.53 min

- Details of fitted regression line (log k' vs. log Koc soil, 1st injection):
y = 2.858x + 3.012
R² = 0.951
- Details of fitted regression line (log k' vs. log Koc soil, 2nd injection):
Y = 2.858x + 3.012
R² = 0.951
- Details of fitted regression line (log k' vs. log Koc sewage sludge, 1st injection):
Y = 2.941x + 3.282
R² = 0.925
- Details of fitted regression line (log k' vs. log Koc sewage sludge, 2nd injection):
Y = 2.941x + 3.282
R² = 0.925
- Graph of regression line attached: yes
- Average retention data for test substance: 5.32 min (refer also to table 1: "Results of retention times, capacity factors k’, log k’ and adsorption coefficient for vinylcyclohexane" below)

Table 1: Results of retention times, capacity factors k’, log k’ and adsorption coefficient for vinylcyclohexane

Vinylcyclohexane Retention time tr in min Capacity factor k´ log k' Adsoption coefficient
log Koc, soil log Koc, sewage sludge
First injection  5.32 0.56 -0.25 2.29 2.54
Second injection  5.32 0.56 -0.25 2.29 2.55
Validity criteria fulfilled:
yes
Conclusions:
Based on the OECD guideline 121, the adsorption coefficients (Koc) of vinylcyclohexane on soil and on sewage sludge were estimated by using high performance liquid chromatography (HPLC). Due to the structural differentiation between test item and the reference substances listed in the OECD Guideline 121, six structurally heterogeneous substances were used for the study. For the dead time determination urea was used. The proposed method is reproducible and specific. The estimated results for vinylcyclohexane are log Koc, soil = 2.29 and log Koc, sewage sludge = 2.55.
Executive summary:

To estimate the adsorption of vinylcyclohexane on soil and sewage sludge, an GLP experiment was conducted in accordance with OECD guideline 121. The HPLC method for estimating the adsorption coefficient is carried out on an analytical separation column, which is filled with a commercial cyanophase. This stationary phase allows a similar interaction between polar and nonpolar groups of a molecule like organic matter in soil – sewage matrices. With the gained retention times a relationship between retention and the adsorption coefficient can be established. For each substance the capacity factor is calculated with the retention time. The logarithms of the capacity factors Koc are plotted against the logarithms of the capacity factors k 'and the calibration line is calculated by means of linear regression. The test item was prepared by weighing of 200 mg in a 20-mL volume flask, dissolving in methanol and a 1:20 dilution with mobile phase. The measurements were performed in duplicate.

Vinylcyclohexane was analysed with HPLC-UV/VIS. The adsorption parameters were calculated using the Freudlich adsorption isotherm.

 

The adsorption log Koc values were 2.29 for soil and 2.55 for sewage sludge.

 

Results Synopsis:

 

Soil type: soil and sewage sludge

Log Koc soil: 2.29

Log Koc sewage sludge: 2.55

 

Study Acceptability:  This study is classified as acceptable and satisfies the guideline requirement for an adsorption/desorption study in soil.

Description of key information

Based on the OECD guideline 121, the adsorption coefficients (Koc) of vinylcyclohexane on soil and on sewage sludge were estimated by using high performance liquid chromatography (HPLC). The estimated results for vinylcyclohexane are log Koc, soil = 2.29 and log Koc, sewage sludge = 2.55.

Key value for chemical safety assessment

Koc at 20 °C:
195

Other adsorption coefficients

Type:
other: Log Koc, soil
Value in L/kg:
2.29
at the temperature of:
25 °C

Other adsorption coefficients

Type:
other: Log Koc, sewage sludge
Value in L/kg:
2.55
at the temperature of:
25 °C

Additional information