2-ethylhexyl (4-chloro-2-methylphenoxy)acetate

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20.09.2005 - 03.03.2006.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Reason / purpose for cross-reference:

read-across source

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2006

Report date:

2006

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Test material

Test material information

Constituent 1

Reference substance name:

(4-chloro-2-methylphenoxy)acetic acid

EC Number:

202-360-6

EC Name:

(4-chloro-2-methylphenoxy)acetic acid

Cas Number:

94-74-6

Molecular formula:

C9H9ClO3

IUPAC Name:

(4-chloro-2-methylphenoxy)acetic acid

impurity 1

Reference substance name:

Water

EC Number:

231-791-2

EC Name:

Water

Cas Number:

7732-18-5

Molecular formula:

H2O

IUPAC Name:

water

impurity 2

Reference substance name:

4-chloro-o-cresol

EC Number:

216-381-3

EC Name:

4-chloro-o-cresol

Cas Number:

1570-64-5

Molecular formula:

C7H7ClO

IUPAC Name:

4-chloro-2-methylphenol

Test material form:

solid

Study design

Batch equilibrium or other method

Matrix properties

Matrix properties 1

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

16

% Silt:

19

% Sand:

65

% Org. carbon:

6.1

pH:

6.18

CEC:

22.2 other: cmol/kg

Bulk density (g/cm³):

1.02

Matrix properties 2

Matrix no.:

#2

Matrix type:

silt loam

% Clay:

6

% Silt:

76

% Sand:

18

% Org. carbon:

1.7

pH:

5.56

CEC:

8 other: cmol/kg

Bulk density (g/cm³):

1.18

Matrix properties 3

Matrix no.:

#3

Matrix type:

loamy sand

% Clay:

10

% Silt:

21

% Sand:

69

% Org. carbon:

1.4

pH:

4.04

CEC:

3.3 other: cmol/kg

Bulk density (g/cm³):

1.46

Matrix properties 4

Matrix no.:

#4

Matrix type:

Silt

% Clay:

21

% Silt:

76

% Sand:

3

% Org. carbon:

1.5

pH:

5.65

CEC:

11.5 other: cmol/kg

Bulk density (g/cm³):

1.18

Matrix properties 5

Matrix no.:

#5

Matrix type:

silt loam

% Clay:

14

% Silt:

72

% Sand:

14

% Org. carbon:

1.6

pH:

5.33

CEC:

9.8 other: cmol/kg

Bulk density (g/cm³):

1.19

Details on matrix:

pH in 0.01 M CaCl2

Results and discussion

Adsorption coefficient

Adsorption coefficient 1

Key result

Sample No.:

#1

Type:

Koc

Value:

25.41 L/kg

Adsorption coefficient 2

Key result

Sample No.:

#2

Type:

Koc

Value:

44.12 L/kg

Adsorption coefficient 3

Key result

Sample No.:

#3

Type:

Koc

Value:

214.29 L/kg

Adsorption coefficient 4

Key result

Sample No.:

#4

Type:

Koc

Value:

86.67 L/kg

Adsorption coefficient 5

Key result

Sample No.:

#5

Type:

Koc

Value:

62.5 L/kg

Applicant's summary and conclusion

Executive summary:

The aim of the study was to evaluate the adsorption and desorption of the test material in five soil types (marked as I, II, III, IV and V) with a different physical and chemical properties.

The methodical basis of the study was OECD Guideline No 106, corresponding to EU method C.18 and Good Laboratory Practice (GLP).

The study comprised three tiers. The purpose of the Tier I (preliminary study) was to determine optimal soil: solution ratio, the equilibrium time for adsorption and the amount of the test material adsorbed at equilibrium, as well as to determine stability of the test substance during the test period. Two replicates were prepared at each sampling time.

To preliminary study two different types of soil (marked as I and IV) were used. In this study following the soil/solution ratios were tested: 1:2.5, 1:5 and 1:25. Initial concentration of the test material in aqueous phase was 10µg/cm³. The same concentration of the test material in the studies of adsorption and desorption kinetics was used. Samples to analysis were taken after 30 minutes and after 1, 2, 4, 6 and 24 hours contact of the test material with soil mixture.

The experiment was performed by using parallel method. Samples with the same soil: solution ratio were prepared, as many as the time intervals at which analysis was performed.

In Tier II (screening test) the adsorption in five different soil types was studied by means of adsorption kinetics at a single concentration of the test material. Distribution coefficients for adsorption (K_d) and organic carbon normalized adsorption coefficient (Ic_e) were determined as well. In the experiment were used on three additional soils marked as II, III and V. The study was not repeated for soils tested in preliminary study. The experiment was performed by using parallel method. Analyses were done after 30 minutes and after 1, 2, 4, 6 and 24 hours of contact of the test material with soil.

In Tier III Freundlich adsorption isotherms were determined to evaluate the influence of concentration on the extent of adsorption on soils. In tier III desorption kinetics were done as well.

Five concentrations of the test material in aqueous phase were used in adsorption isotherms study: 0.5; 5; 10; 25 and 50 µg/cm³. The aqueous phase was analyzed only once at the time necessary to reach equilibrium.

The study concerning desorption kinetics was also performed in five soil types. All soil mixtures with the solution were shaken until to reach adsorption equilibrium. Then, the phases were separated by centrifugation and the aqueous phases were removed. The volume of solution removed was replaced by an equal volume of 0.01 M CaC1₂. Experiment was performed by parallel method Samples were taken to the analysis after 30 minutes and after 1, 2, 4, 6 and 24 hours.

In all tiers of the study aqueous phase obtained after centrifugation and filtration of the soil suspensions was analysed (indirect method).

Chemical analysis was performed by using solid phase extraction method and in the final analysis by means of liquid chromatogrphy with UV-VIS detector.

On the basis of the results obtained in the preliminary study and calculated distribution coefficientsKdsoil: solution ratio 1:2.5 for further tiers of the study was chosen. Equilibrium time was reached after 6 hours of the experiment.

The analysis of control samples confirmed the stability of the test material during the test period.

The distribution coefficients (K_d) assigned during adsorption kinetics were 1.6; 0.8; 3.0; 1.3 and 1.0 cm³/g for I, II, III, IV and V soils, respectively.

Organic carbon normalized adsorption coefficients (K_oc) were 25.41; 44.12; 214.29; 86.67 and 62.50 cm³/g for I, II, III, IV and V soils, respectively.

Freundlich adsorption coefficients(KF^ads)were 2.23; 1.72; 4.02; 2.15 and 2.55 µeⁿ(cm³)^1/n/g for I, II, III, IV and V soils, respectively.

Apparent desorption coefficients (K_des) were 10.54; 14.56; 5.64; 10.22 and 14.03 cm³/g for I, II, III, IV and V soils, respectively.