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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:
Report date: 2012-09-06
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented study performed according to relevant guidelines. However not performed under GLP.
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:
no
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Test temperature:
Column temperature: 40 deg C
Details on study design: HPLC method:
Principle of the method:
HPLC is performed on analytical columns packed with commercially available cyanopropyl solid phase containing lipophilic and polar moieties. A moderately polar stationary phase based on silica matrix is used. While passing through the HPLC column along with the mobile phase the test substance interacts with the stationary phase. As a result of partitioning between mobile and stationary phases the test substance is retarded.

Procedure
The distribution coefficient was estimated by the HPLC method using isocratic elution. The HPLC system was calibrated for log k' versus log Koc using reference substances of known log Koc. Test substance was dissolved in tetrahydrofurane. Calibration solutions were prepared in acetonitrile.
Test substance solution: 12.1 mg in 50 ml tetrahydrofurane
Calibration solutions: approx. 5-10 µg/ml in acetonitrile
Dead time marker: sodium nitrate

Instrumental conditions
HPLC instrument: Agilent 1100
Injection volume: 5 µl
Reference substances see table under "any other informations on materials and methods inc. tables"
Detector: UV (DAD), 254 nm (test substance) and 220 nm (calibration)
Column: µBondapak CN, 150 mm x 3.1 mm, 10 µm
Mobile phase: water/acetonitril = 55/45 (v/v)
Flow rate: 1 ml/min
Column temperature: 40 deg C

Evaluation of results performed according to the guideline.
Type:
log Koc
Value:
> 5
Temp.:
40 °C
Remarks on result:
other: HPLC method: Reference of highest log Koc used: DDT (log Koc 5.63) - by linear extrapolation (R^2= 0.9869) a log Koc of 6.2 was derived for the test item. Column temperture 40 deg C
Details on results (HPLC method):
Calibration line and evaluation:
From the calibration line log K' versus log Koc the following equation was calculated:
Y = 0.1522x-0.0768, with R^2 = 0.9869

For the test substance, k' was determined as 7.25, log k' = 0.86

From this, the log Koc of the test substance was estimated as follows:

log Koc = (log(k') - b)/a = [0.86 - (-0.0768)]/0.1522 = 6.2

The calculated log Koc value of the test substance is outside the calibrated range. 4,4'-DDT is the reference substance with highest log Koc value available. Therefore only an extrapolated value for the test substance can be obtained.

Analytical data:

Substance

log Koc
value

Inj. 1
t
R[min]

Inj. 2
t
R[min]

k'

log k'

mass on
column
[µg]

Sodium nitrate

--

0.839

0.841

---

---

50

Acetanilide

1.25

1.882

1.883

1.24

0.09

55

Phenol

1.32

1.944

1.943

1.31

0.12

53

Methylbenzoate

1.8

2.217

2.217

1.64

0.21

43

Naphthalene

2.75

2.827

2.827

2.37

0.37

8

1,2,3-Trichlorobenzene

3.16

3.024

3.025

2.60

0.42

48

Phenanthrene

4.09

3.462

3.463

3.12

0.49

28

4,4'-DDT solution

(100 ng/µl)

5.63

6.075

6.080

6.24

0.80

25

Test substance

--

6.938

6.922

7.25

0.86

1210

Validity criteria fulfilled:
yes
Conclusions:
In a raliable study using the HPLC-method according to OECD 121 for estimating the adsorption coefficient Koc on soil and sewage sludge, for the test item a log Koc of >5.0 was determined. The reference substance of highest log Koc used was DDT (log Koc 5.63). The linear regression from the calibration curve gives a solid result with R^2= 0.9869. Thus, by linear extrapolation a log Koc of 6.2 was estimated for the test item.
Executive summary:

In a reliable study (not performed under GLP: reliability category 2) the sorption behaviour (log Koc) of the test substance on soil and on sewage sludge was estimated using high performance liquid chromatography (HPLC) according to the OECD Guideline for the Testing of Chemicals 121 (2001). 7 compounds with log Koc-values between 1.25 and 5.63 were used for calibration. From the capacity factor k' of 7.25 for the test item and the calibration curve a log Koc of >5.0 was determined.

The reference substance of highest log Koc used was DDT (log Koc 5.63). The linear regression from the calibration curve gives a solid result with R^2= 0.9869. Thus, by linear extrapolation a log Koc of 6.2 was estimated for the test item.

Description of key information

In a reliable study using the HPLC-method according to OECD 121 for estimating the adsorption coefficient Koc on soil and sewage sludge, for the test item a log Koc of >5.0 was determined. The reference substance of highest log Koc used was DDT (log Koc 5.63). The linear regression from the calibration curve gives a solid result with R^2= 0.9869. Thus, by linear extrapolation a log Koc of 6.2 was estimated for the test item.

Key value for chemical safety assessment

Koc at 20 °C:
6.2

Additional information

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