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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline Study
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Type of method:
batch equilibrium method
Media:
other: Soil and sediment
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material: No surrogate or analogue material was used.
Test temperature:
No details available.
Details on study design: HPLC method:
Not applicable.
Analytical monitoring:
yes
Details on sampling:
No details available.
Details on matrix:
PODZOL: 4.85 % Corg, pH 2.8, 15.1 mval CEC, 89.2 % Sand, 8.2 % Silt, 2.6 % Clay
ALFISOL: 1.25 % Corg, pH 6.7, 12.3 mval CEC, 0.4 % CaCO3, 69.7 % Sand, 14.4 % Silt, 15.9 % Clay
SEDIMENT: 1.58 % Corg, pH 7.1, 13.4 mval CEC, 38.9 % CaCO3, 5.5 % Sand, 58.8 % Silt, 35.7 % Clay
Details on test conditions:
50 mL of the test solution were added to 10 g (dry weight) of the specific soils. The soil samples were shaken for 0.5, 1, 1.5, 5, 24, 72 hours, respectively. Thean an aliquot of 1 mL of the water-phase was removed and the concentration of the substance in the aqueous phase was determined. As for all investigated substances the sorption equilibrium was reached within 16 hours, the Freundlich isotherms were determined after an incubation period of 16 hours. The initial concentrations used were about 15 mg/L, 5 mg/L and 0.15 mg/L. After reaching the equilibrium the soil samples were centrifuged, decanted, and the concentrations in the supernatant were determined by means of GC, HPLC or szintillation measurements (von Oepen, 1990). All samples were determined in parallel. One control and one blank were investigated additionally. After the adsorption step a two step desorption test was performed with an equilibrium time of 8 hours followed by a desorption period of 16 hours. When necessary, the mass balance was determined, using a mixture of Acetonitrile/0.01 M CaCl2/Acetic Acid (80/18/2). The Freundlich constants and koc values were calculated.
Computational methods:
No computational methods are reported.
Type:
Koc
Value:
4
% Org. carbon:
4.85
Remarks on result:
other: Podzol
Type:
Koc
Value:
163
% Org. carbon:
1.25
Remarks on result:
other: Alfisol
Type:
Koc
Value:
508
% Org. carbon:
1.58
Remarks on result:
other: Sediment
Details on results (HPLC method):
Not applicable.
Adsorption and desorption constants:
No details available.
Recovery of test material:
No details available.
Concentration of test substance at end of adsorption equilibration period:
No details available.
Concentration of test substance at end of desorption equilibration period:
No details available.
Transformation products:
not measured
Details on results (Batch equilibrium method):
The sorption equilibrium was reached within 16 hours. The sorption was reversible to a great extent. The mass balance resulted in a recovery > 80 %.
Statistics:
No statistics reported.
Validity criteria fulfilled:
yes
Remarks:
Batch-equilibrium studies are appropriate to determine sorption coefficients according to OECD Guideline 106.
Conclusions:
The publication describes a valid method to determine the adsorption coefficient of the test substance with the batch-equilibrium method according to OECD Guideline 106.
Executive summary:

The publication reports about a batch-equilibrium method according to OECD Guideline 106, whereby the test substance was investigated beside 49 substances (von Oepen, Kördel and Klein, 1991). Three types of soil were used: Podzol with a organic carbon content of 4.85 %, Alfisol with 1.25 % organic carbon and Sediment with 1.58 % organic carbon, respectively. The sorption equilibrium was reached within 16 hours and it was reversible to a great extent. The mass balance resulted in a recovery of greater than 80 %. For hydrophobic compounds, variation in the koc-values of different sorbants is within one order of magnitude. For more polar compounds (like amines), the variation in sorption coefficients is up to two orders of magnitude. The sorption of amino-groups to clay-minerals or pH-dependent sorption of acids play a key role. Although several interactions contributing to the sorption process are known, it was not possible to determine the quantitative contribution of each sorption mechanism. For the test substance, the Koc values were reported as followed for Podzol, Alfisol and Sediment: 4, 163 and 508, respectively. Therefore, the geometric mean of the Koc for soil is determined as 25.53.

Description of key information

The key value is the geometric mean of the Koc for soil determined according to OECD Guideline 106 (von Oepen, Kördel and Klein, 1991). 

Key value for chemical safety assessment

Koc at 20 °C:
25.53

Additional information

A publication is available about a batch-equilibrium method according to OECD Guideline 106, whereby the test substance was investigated beside 49 substances (von Oepen, Kördel and Klein, 1991). Three types of soil were used: Podzol with an organic carbon content of 4.85 %, Alfisol with 1.25 % organic carbon and Sediment with 1.58 % organic carbon, respectively. The sorption equilibrium was reached within 16 hours and it was reversible to a great extent. The mass balance resulted in a recovery of greater than 80 %. For hydrophobic compounds, variation in the Koc-values of different sorbents is within one order of magnitude. For more polar compounds (like amines), the variation in sorption coefficients is up to two orders of magnitude. The sorption of amino-groups to clay-minerals or pH-dependent sorption of acids play a key role. Although several interactions contributing to the sorption process are known, it was not possible to determine the quantitative contribution of each sorption mechanism. For the test substance, the Koc values were reported as followed for Podzol, Alfisol and Sediment: 4, 163 and 508, respectively. Therefore, the geometric mean of the Koc for soil is determined as 25.53.

As supporting information, the computer tool EPIWIN calculates the soil adsorption coefficient also concerning the MCI method, which gave a Koc of 8.158 L/kg (Chemservice S.A., 2010).

The adsorption coefficients for Montmorillonite, Kaolinite, and marine sediment were determined in a batch equilibrium experiment by Wang and Lee (1993). Beside the different adsorption coefficients (please refer to table 9 Overview of studies on adsorption / desorption), the scientists presented the following statements: Adsorption of amines by Montmorillonite and Kaolinite is consistent with control by electrostatic attraction as well as by van der Waals forces and this could be an important control on the distribution of these organic compounds in sediment porewaters. Adsorption of amines by clays and also by FP sediment is essentially a reversible process.

In a study conducted by Wang and Lee in former times (1990), the adsorption coefficient of marine sediment was determined as 2.4 - 4.7, whereby salinity will significantly reduce the adsorption of amines onto freshwater sediments. Beside the soil adsorption procedure, removal of amines from uncontaminated seawater can occur by bacterial uptake (incorporation plus respiration). In relationship to the organic and clay mineral content, the exchangeable and fixed dimethylamine concentration will vary among different sediments. In Flax point sediment seasonal variations were observed for the concentrations of dimethylamine.