C.I. Reactive Yellow 161

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Jan - Mar 2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2000

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

20°C

Details on study design: HPLC method:

HPLC calibration:

- Preliminary test: a Stock solution was prepared by dissolving 32.11 g test item in 200 mL purified water. Considering the purity, the stock solution contained 0.128 µg of the test item /mL.
- Screening Test: the calibration solutions were freshly prepared in the same way as for the preliminary test. Stock solution I was prepared by dissolving 41.14 mg test item in 200 ml purified water. An aliquot of 10 mL of stock solution I was diluted to 100 mL with purified water (stock solution II). The final concentration of stock solution II was 20.57 µg test item/mL. Considering the purity, stock solution II contained 16.41 µg of the test item /mL.

HPLC methodology:

HPLC was used to analyse the test item in the supernatant solutions from the adsorption and desorption tubes for each soil.
Pump: Merck-Hitachi L-7100
Autosampler: Merck-Hitachi L-7200
UV-detector: Merck-Hitachi L-7400 (430 nm)
Precolumn: C18
Column: 15 cm x 4.6 mm, 5 µm Discovery C18
Temperature: Room temperature (about 20 °C)
Mobile Phase:
Solvent A: Acetonitrile/water/phosphate buffer (pH 7) 7/2/1 (v/v/v)
Solvent B: Acetonitrile/water/phosphate buffer (pH 7) 1/8/1 (v/v/v)
Each of the solvents A and B contained 0.2% tetrabutyl ammonium bromide.
The limit of quantitation of the test item corresponded to the lowest calibration point used and was set to 0.02 µg/mL.

Analytical monitoring:

yes

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

8.1

% Silt:

16.6

% Sand:

75.3

% Org. carbon:

2.3

pH:

5.6

CEC:

11 other: mmol/100 g soil

Matrix no.:

#2

Matrix type:

loam

% Clay:

17.57

% Silt:

37.12

% Sand:

45.31

% Org. carbon:

1.28

pH:

7.37

CEC:

11.4 other: mmol/100 g soil

Matrix no.:

#3

Matrix type:

silty clay loam

% Clay:

34.04

% Silt:

46.94

% Sand:

19.02

% Org. carbon:

2.67

pH:

5.42

CEC:

26.95 other: mmol/100g soil

Matrix no.:

#4

Matrix type:

clay loam

% Clay:

36.42

% Silt:

42.44

% Sand:

21.14

% Org. carbon:

4.67

pH:

7.53

CEC:

40.75 other: mmol/100 g soil

Matrix no.:

#5

Matrix type:

silt loam

% Clay:

17.4

% Silt:

65.23

% Sand:

17.37

% Org. carbon:

2.11

pH:

5.7

CEC:

12.83 other: mmol/100 g soil

Details on matrix:

COLLECTION AND STORAGE
Soil I was sampled by LUFA (Landwirtschaftliche Untersuchungs- und Forschungsanstalt, Speyer 2.2, Germany, 49°18' N, 8°26' E) from the top 20-cm soil layer in January 2003. The soil was sieved through a 2 mm sieve by LUFA. An aliquot was stored at RCC Ltd. air-dried until use.

Soil II was sampled by RCC Ltd from the top 30-cm soil layer from an agricultural area in Mechtildshausen (D-65205 Wiesbaden-Erbenheim, Domaine Mechtildshausen/ Germany, 50° 02' N, 8° 18' E) in June 2003. The soil was then sieved through a sieve of 2 mm by RCC Ltd prior to use and stored air-dried.

Soil III was freshly sampled by SADEF (France) from the top 20-cm soil layer from an agricultural area in Uffholtz (Alsace (68700)/France, 47°49' N, 7°10' E) in June 2001. The soil was then sieved through a sieve of 2 mm by RCC Ltd prior to use and stored air-dried.

Soil IV was freshly sampled by SADEF (France) from the top 20-cm soil layer from an agricultural area in Mussig (Bas Rhin (67600)/France, 48°14' N, 7°31' E) in October, 2001. The soil was then sieved through a sieve of 2 mm by RCC Ltd prior to use and stored airdried.

Soil V (Bretagne 1) was sampled by SADEF Services from the top 0 to 20 cm soil layer from an agricultural area in Moréac (Réguiny (56190)/France, 47°55' N, 2°49' E) on October, 2001. The soil was then sieved through a sieve of 2 mm by RCC Ltd prior to use and stored air-dried.

Sieving was performed with minimal force, so that the original texture of the soil was changed as little as possible. The soil moisture content of each soil was determined with two aliquots by heating up to 120 °C until there was no significant change in weight.

Details on test conditions:

Adsorption of the Test Item to Soil
Following application, the test tubes were shaken horizontally at about 150 strokes per minute at 20 °C. After shaking, the soils were centrifuged (10 minutes at about 3300 rpm at room temperature) and the supematants were decanted into tared, labelled sample containers. The volumes of the supematants were determined gravimetrically. In the preliminary and screening test, samples were removed for HPLC analysis at different shaking
intervals (after centrifugation).

The equilibrium concentration of the test item, and its total amount in the aqueous phase, were calculated based on the results of the HPLC analyses. The amount of test item adsorbed onto soil particles was obtained from the difference between the initial and final amount of test item in the aqueous phase. Only for the mass balance tubes, the amount of the test item adsorbed to soil was additionally quantitatively analysed by extraction and
HPLC analysis.

Desorption of the Test Item
The same volume of 0.01 M CaCI2 as used for the adsorption was added back to the soil pellet after removal of the adsorption supernatant. Thereafter, desorption mixtures were agitated in the same manner as for the adsorption step. Samples were then centrifuged and the supernatant analysed by HPLC, after either 24 hours or 48 hours of shaking.

Key result

Sample No.:

#1

Type:

log Koc

Value:

3.46 dimensionless

pH:

5.6

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

2.3

Key result

Sample No.:

#2

Type:

log Koc

Value:

3.71 dimensionless

pH:

7.37

Temp.:

20 °C

Matrix:

Loam

% Org. carbon:

1.28

Key result

Sample No.:

#3

Type:

log Koc

Value:

3.73 dimensionless

pH:

5.42

Temp.:

20 °C

Matrix:

Silty clay loam

% Org. carbon:

2.67

Key result

Sample No.:

#4

Type:

log Koc

Value:

3.74 dimensionless

pH:

7.53

Temp.:

20 °C

Matrix:

Clay loam

% Org. carbon:

4.67

Key result

Sample No.:

#5

Type:

log Koc

Value:

3.95 dimensionless

pH:

5.7

Temp.:

20 °C

Matrix:

Silt loam

% Org. carbon:

2.11

Adsorption and desorption constants:

The adsorption coefficients Koc (ads) were calculated to be 2893 cm³/g for soil I (loamy sand), 5155 cm³/g for soil II (loam), 5410 cm³/g for soil III (silty clay loam), 5465 cm³/g for soil IV (clay loam) and 8867 cm³/g for soil V (silt loam). The resulting apparent Koc (des) values were calculated to be 6524 cm³/g for soil I (loamy sand), 6663 cm³/g for soil II (loam), 6357 cm³/g for soil III (silty clay loam), 7439 cm³/g for soil IV (clay loam) and 19181 cm³/g for soil V (silt loam).

Recovery of test material:

The percentage of the applied test item that was adsorbed after 24 hours was 72.5% of the initial amount for soil I (loamy sand), 73.0% for soil II (loam), 85.2% for soil III (silty clay loam), 91.1% for soil IV (clay loam) and 87.8% for soil V (silt loam). Blank samples showed no signals at the retention time of the test item. The concentration in the control samples remained above 90% throughout the incubation period of 24 hours.

Concentration of test substance at end of adsorption equilibration period:

I: 0.14; II: 0.14; III: 0.08; IV: 0.05; V: 0.06 mg/L

Concentration of test substance at end of desorption equilibration period:

I: 0.07; II: 0.06; III: 0.06; IV: 0.03; V: 0.03 mg/L

Sample no.:

#1

Duration:

48 h

% Adsorption:

9.3

Sample no.:

#2

Duration:

48 h

% Adsorption:

9.3

Sample no.:

#3

Duration:

48 h

% Adsorption:

10.9

Sample no.:

#4

Duration:

48 h

% Adsorption:

11.7

Sample no.:

#5

Duration:

48 h

% Adsorption:

11.2

Sample no.:

#1

Duration:

24 h

% Desorption:

27.4

Sample no.:

#1

Duration:

48 h

% Desorption:

7.9

Sample no.:

#2

Duration:

24 h

% Desorption:

23.1

Sample no.:

#2

Duration:

48 h

% Desorption:

21.2

Sample no.:

#3

Duration:

24 h

% Desorption:

17.4

Sample no.:

#3

Duration:

48 h

% Desorption:

9.2

Sample no.:

#4

Duration:

24 h

% Desorption:

8.1

Sample no.:

#4

Duration:

48 h

% Desorption:

5.2

Sample no.:

#5

Duration:

24 h

% Desorption:

4.2

Sample no.:

#5

Duration:

48 h

% Desorption:

7

Transformation products:

not measured

Details on results (Batch equilibrium method):

The adsorption of the test item does not depend on the organic carbon content of the soil. There is no correlation of Kd to one of the soil parameters, indicating a complex adsorption behaviour. The adsorption of the test item is much higher than could be expected by its water solubility of approximately 100 g/L. Desorption coefficients are higher than the adsorption coefficients demonstrating the in part irreversibility of the adsorption process. Results indicate that the test item can be considered to have only a slight mobility potential.

Validity criteria fulfilled:

yes

Conclusions:

The log Koc (ads.) values for the test item range between 3.46 and 3.95 not depending in the organic carbon content of the soil (OECD 106). Desorption coefficients are higher than the adsorption coefficients demonstrating the in part irreversibility of the adsorption process. The overall sesults indicate that Reactive Yellow 161 can be considered to have only a slight mobility potential.

Description of key information

The log Koc (ads.) values for the test item range between 3.46 and 3.95 not depending in the organic carbon content of the soil (OECD 106, five soil types tested). Desorption coefficients are higher than the adsorption coefficients demonstrating the in part irreversibility of the adsorption process. The overall sesults indicate that Reactive Yellow 161 can be considered to have only a slight mobility potential.

Key value for chemical safety assessment

Koc at 20 °C:

3.95