6,6',6''-(1,3,5-triazine-2,4,6-triyltriimino)trihexanoic acid

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995-03-03 to 1995-06-08

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP study, OECD study guideline

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

other: soil/water

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Concentrations: For the determination of the adsorption isotherms, adsorption tests were performed using different levels of substance concentration. The confirrmation by HPLC (control values) gave the following test concentration: 497 µg/L, 126 µg/L, 69 µg/L, 51 µg/L.
- Sampling interval: after 2, 4, 6, 24, 48 and 72 h

Details on matrix:

PROPERTIES
Five soils varying considerably in their physico-chemical properties were used for the test.
Eurosoil 1:
- % sand: 3.3
- % silt: 21.9
- % clay: 75
- pH: 5.9 (water)
- Organic carbon (%): 1.30
- CEC (meq/100 g): 29.9

Eurosoil 2:
- % sand: 13.4
- % silt: 64.1
- % clay: 22.6
- pH: 8.0 (water)
- Organic carbon (%): 3.70
- CEC (meq/100 g): 28.3

Eurosoil 3:
- % sand: 46.4
- % silt: 36.8
- % clay: 17.0
- pH: 5.8 (water)
- Organic carbon (%): 3.45
- CEC (meq/100 g): 18.3

Eurosoil 4:
- % sand: 4.1
- % silt: 75.7
- % clay: 20.3
- pH: 7.0 (water)
- Organic carbon (%): 1.55
- CEC (meq/100 g): 17.5

Eurosoil 5:
- % sand: 81.6
- % silt: 12.7
- % clay: 6.0
- pH: 4.6 (water)
- Organic carbon (%): 9.23
- CEC (meq/100 g): 32.7

Details on test conditions:

TEST SYSTEM
- Measuring equipment:
Photometer
- Method of preparation of test solution:
Because of the low water solubility of the test substance two different possibilities for preparing a (nearly) saturated solution of Irgacor L 190 in 0.01 M CaCl2-solution were tested:
1. (following the OECD test guideline 105 „Water solubility" (reference 5))
About 5 g of the test substance were soluted in a suitable solvent (f.i. methanol), suspended with silica gel and the solvent removed by a rotavapor. Afterwards about 3 - 4 L of a 0.01 M CaCl2-solution was constantly passed through a column, which was filled with the solvent-free silica gel. The CaCl2-solution was collected in fractions of about 250 -500 ml. The content of the test substance was determined by HPLC in each fraction. The fractions whithin the plateau (of the test substance concentration) will be combined and used for the test.
2. (saturated solution)
6 mg of the test substance were diluted with 1 L 0.01 M CaCl2-solution and stirred or shaked for a longer time (about 1 h). After about 24 h the solution is stirred again for about 20 min and afterwards filtered through a membrane filter (0.45 pm) to remove non diluted particles. In a pretest both ways had given approximately same results. Therefore the second method for preparing a (nearly) saturated solution of test item was used during the study. The filtering of the (nearly) saturated solution achieves a sterilization of the solution, too. The saturated solution was diluted 1:2 with 0.01 M CaCl2-solution. This solution was used for kinetics and adsorption/desorption tests, whereas further dilutions in 0.01 M CaCl2-solution were prepeared for adsorption isotherms. The concentrations of test item in the test solution as well as in the diluted solutions were determined by HPLC.

Computational methods:

The adsorption partition coefficient k' is calculated by dividing the concentration of the substance in the soil by the concentration in the aqueous phase.
k' = X/m / Ce
k' = adsorption partition coefficient
X/m [µg/g] = concentration of substance in the soil after adsorption
Ce [mg/L] = concentration of substance in the supernatant after adsorption
Normalization of the adsorption partition coefficient k' to the content of organic carbon (%Corg.) of the soil gives the K'oc-value:
K'oc = (k'*100)/%Corg
The empirical Freundlich isotherm has proved to be successful for determining adsorption coefficients independently of concentrations.
X/m = Kf * Ce 1/n or log (X/m) = log Kf + 1/n * log Ce
Kf = adsorption coefficient (log Kf = intercept of the regression line)
1/n = slope of the regression line according to Freundlich
When plotting the log Ce - values against log (X/m) - values, 1/n is the slope of regression line and log Kf the intercept of the y-axis. Using this evaluation, adsorption coefficients at infinitely small concentrations can be obtained. Normalization of the adsorption coefficient Kf to the content of organic carbon (% Corg.) of the soil gives the Koc - value:
Koc = (Kf* 100) / % Corg

Type:

Koc

Value:

32 618

% Org. carbon:

1.3

Remarks on result:

other: Eurosoil 1

Type:

Koc

Value:

709

% Org. carbon:

3.7

Remarks on result:

other: Eurosoil 2

Type:

Koc

Value:

2 575

% Org. carbon:

3.45

Remarks on result:

other: Eurosoil 3

Type:

Koc

Value:

423

% Org. carbon:

1.55

Remarks on result:

other: Eurosoil 4

Type:

Koc

Value:

20 867

% Org. carbon:

9.23

Remarks on result:

other: Eurosoil 5

Type:

other: k' adsorption partition coefficient

Value:

26

Remarks on result:

other: Eurosoil 2, pH 7.4 CaCl2

Type:

other: k' adsorption partition coefficient

Value:

7

Remarks on result:

other: Eurosoil 4, pH 6.5 CaCl2

Type:

other: k' adsorption partition coefficient

Value:

89

Remarks on result:

other: Eurosoil 3, pH 5.2 CaCl2

Type:

other: k' adsorption partition coefficient

Value:

424

Remarks on result:

other: Eurosoil 1, pH 5.1 CaCl2

Type:

other: k' adsorption partition coefficient

Value:

1 926

Remarks on result:

other: Eurosoil 5, pH 3.2 CaCl2

Recovery of test material:

Eurosoil 1: 2.8
Eurosoil 2: 20.8
Eurosoil 3: 5.7
Eurosoil 4: 94.82
Eurosoil 5: 0.84

Concentration of test substance at end of adsorption equilibration period:

adsorption kinetics of test item could only completely determined for Eurosoil 2. For the other Eurosoils some or all values of the concentration in equilibrium state were below the detection limit. Therefore the adsorption as well as the K'oc-values could only be estimated at the detection limit.

Concentration of test substance at end of desorption equilibration period:

The desorption rates could not exactly determined because of very low equilibrium concentrations, which were at the detection limit. The desorption rates were < 1 % and only for Eurosoil 2 the desorption rates (sum of both desorption steps) were between 3 and 8 %.

Transformation products:

no

Details on results (Batch equilibrium method):

The sorption of the substance was not reversible. Only very small amounts of the adsorbed test substance could desorbed by 0.01 M CaCl-Solution and removed by organic solvent extraction from the soil. There are processess leading to an irreversible binding of the test substance to the soil.
The determination of sorption isotherms according to the 'Freundlich'-equation were not possible. In many cases the values of the concentration in equilibrium state were at or below the detection limit (2.2 pg/l, calculated). It was not possible to evaluate some of the
experimental data because of very low concentrations of the test substance and/or interferences with soil matrix constituents.
Therefore the K'oc-values were determined using the results of the adsorption/desorption (16 h-value) and the adsorption kinetics (24 h-value / soil 4).

Description of key information

In a test on adsorption/desorption according to OECD 106 Koc values between 423 L/kg and 32618 L/kg were estimated, the geometric mean value being 3500 L/kg.

Key value for chemical safety assessment

Koc at 20 °C:

3 500