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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2002
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))
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil
Radiolabelling:
no
Test temperature:
25°C
Details on study design: HPLC method:
HPLC conditions (HPLC with UV/Vis detector, reversed phase column and aqueous mobile phase):
- Apparatus: Varian Autosampler 9100, Varian Pump ProStar 230, Varian Detector ProStar 310m Jones Column Oven 7990
- Column: Bondapack Phenyl, part. size 5 μm, 300 mm x 3.9 mm
Eluent A: methanol and water (40:60; v/v)
Eluent B: acetonitrile, ethanol and water (50:45:5, v/v/v)
- Mobile phase:
0 min: 100% A, 0% B
0-8 min: 100% A, 0% B
8-15 min: 40% A, 60% B (gradient)
15-17 min: 40% A, 60% B
17-17.1 min: 10% a, 90% B
17.1-22 min: 10% A, 90% B
22-22.1 min: 100% A, 0% B
22.1-28 min: 100% A, 0% B
- Detection: 210 nm for the reference items and for sodium nitrate, 254 nm for the test item solution
- Injection volume: 20 μL
- Flow: 1.0 mL/min

First a test was performed to elute the test substance with methanol/water as eluting solvent and with a CN-column as mentioned in the guideline. The test item was not elutable with these parameters. Therefore the HPLC method was adjusted as described above.

Test system:
- Test item solution:
12.5 mg of test substance were dissolved in methanol (100 mL) to prepare a stock solution of 125 μg/mL. The pH value of the test item solution was determined to be 7.8.
The test item solution was injected three times.
- Reference solutions:
The reference items were chosen from the list given in the OECD guideline no. 121.
Stock solutions of the reference items in methanol were prepared as described: 10 μL of the reference item fenthion and 10 mg of the reference items isoproturon; triadimenol, linuron, 2,4-DDT and pyrazophos, respectively, were each dissolved in 10 mL methanol.
A combined reference solution was prepared by transferring 0.5 mL of the isoproturon, 1 mL of the triadimenol , 0.225 mL of the linuron, 1 mL of the pyrazophos, 0.25 mL of the fenthion and 0.5 mL of the 2,4-DDT stock solution into one volumetric flask and diluting to a volume of 10 mL with methanol. This reference solution was injected six times.
Sodium nitrate (10 mg) was diluted to 10 mL with methanol to obtain a stock solution. The stock solution (10 μL) was diluted to 1 mL with methanol. This sodium nitrate solution was injected two times and was used for the determination of the dead time of the HPLC system.

The whole test item handling was performed under red light.
Type:
Koc
Value:
3 431
Temp.:
25 °C
Remarks on result:
other: HPLC analysis
Type:
log Koc
Value:
3.5
Temp.:
25 °C
Remarks on result:
other: HPLC analysis
Type:
Koc
Value:
>= 3 067
Remarks on result:
other: calculation using water solubility
Type:
Koc
Value:
4 049
Remarks on result:
other: calculation using logPow
Details on results (HPLC method):
The log Koc was calculated using a regression curve (log k' vs. log koc) and was found to be 3.5 which is equal to a Koc value of 3431. In the present study the reference items covered the range of log Koc 1.86 to log Koc 5.63.
The retention times of the individual measurements of the reference items, test item and for the determination of the dead time are given in the section "Any other information on results incl. tables" as well as the mean retention times and the derived capacity factors.
Using the corresponding log Koc values of the reference items from the OECD guideline, the regression coefficient was calculated. The log Koc value of the test item was calculated from the calibration equation.

The chromatography of the test item resulted in one sharp main peak with a welldefined and reproducible retention time. The HPLC method was, therefore, considered to be suitable for the purpose of the study. Based on the chromatographic data, the test substance was considered to be stable during the test procedure.
It was not possible to determine the adsorption coefficient of the test substance with methanol/water as eluting solvent and with a CN-column as mentioned in the guideline. Referring to this a adjusted HPLC method with a gradient system was used. Additionally the adsorption coefficient (Koc) of the test substance was estimated using a calculation method to be 3067 or higher. This means that the test substance is classified as immobile in soils.

In conclusion, the log of the adsorption coefficient (Koc) of the test substance was estimated to be log Koc = 3.5 which is equal to a Koc value of 3431, using the HPLC method.
This value indicates that the test substance is immobile and remains preferably in soil.

Retention times in minutes of the reference items and the test item:

  1st run 2nd run 3rd run 4th run 5th run 6th run
Sodium nitrate (= dead time) 1.728 1.727        

Reference items

Isoproturon 15.249 15.294 15.251 15.273 15.319 15.260
Triadimenol 16.311 16.348 16.316 16.333 16.346 16.325
Linuron 16.928 16.963 16.940 16.948 16.944 16.942
Fenthion 18.476 18.527 18.485 18.477 18.482 18.483
Pyrazophos 18.965 19.021 18.971 18.958 18.965 18.971
DDT 20.825 20.843 20.818 20.809 20.802 20.820
Test item 18.133 18.111 18.139      

Deetemrination of the adsorption coefficient (Koc) of the test substance:

  Number of analysis Mean retention time (min) k' logk' logKoc
Sodium nitrate (= dead time) 2 1.73      

Reference items

Isoproturon 6 15.27 7.84 0.89 1.86
Triadimenol 6 16.33 8.45 0.93 2.40
Linuron 6 16.94 8.81 0.94 2.59
Fenthion 6 18.49 9.70 0.99 3.31
Pyrazophos 6 18.98 9.98 1.00 3.65
DDT 6 20.82 11.05 1.04 5.63
Test item 3 18.13 9.50 0.98 3.54
18.11 9.48 0.98 3.52
18.14 9.50 0.98 3.54
Linear regression slope 0.039
y-axis intercept 0.840
coefficient of regression 0.956
Validity criteria fulfilled:
yes
Conclusions:
The logKoc of the test substance was estimated to be 3.5 at 25 °C which is equal to a Koc value of 3431, using the HPLC method. Therefore, adsorption to solid soil phase is expected.
Executive summary:

In this guideline (OECD 121) study conducted to GLP standards, the test material (EC 438-340-0) was determined to have a logKoc = 3.5 at 25 °C

Description of key information

Study conducted to recognised testing guidelines with GLP.

Key value for chemical safety assessment

Koc at 20 °C:
3 431

Additional information

The determination of the adsorption coefficient of the test substance was performed according to the OECD guideline no. 121 (RCC Ltd. 2002c). The logKoc was found to be 3.5 (Koc = 3431).

Additionally the adsorption coefficient was estimated using a calculation to be 3067 or higher.

These values indicate that the test substance is immobile and remains preferably in soil - adsorption to solid soil phase is expected.

[LogKoc: 3.5]