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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: Comparable to accepted guidelines and standards
Qualifier:
according to
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.
Radiolabelling:
not specified
Test temperature:
No details available.
Details on study design: HPLC method:
Not applicable.
Analytical monitoring:
not specified
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. Then 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.
% Org. carbon:
4.85
Remarks on result:
other: Podzol: no detectable sorption
Type:
Koc
Value:
389
% Org. carbon:
1.25
Remarks on result:
other: Alfisol
Type:
Koc
Value:
449
% 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:
Podzol: Methylamine did not adsorb to soil in detectable amounts.
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.
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 (van Oepen, Kördel and Klein 1991) refers to a batch-equilibrium method according to OECD Guideline 106, whereby methylamine was investigated aside from 49 substances. 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 plays 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 Alfisol and Sediment: 389 and 449, respectively. The test substance did not adsorb to Podzol in detectable amounts.

Description of key information

OECD 106: Koc (soil) = 389; Koc (sediment) = 449

Key value for chemical safety assessment

Koc at 20 °C:
389

Additional information

There are several studies/publications available dealing with the absorption of MMA to soil and/or sediment.

The key study (van Oepen, Kördel and Klein 1991) refers to a batch-equilibrium method according to OECD Guideline 106, whereby methylamine was investigated aside from 49 substances. 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 plays 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 Alfisol and Sediment: 389 and 449, respectively. The test substance did not adsorb to Podzol in detectable amounts.

 

Further information on adsorption is contained in the supporting studies.

 

Wang and Lee (1993) investigated the adsorption and desorption behaviour of monomethylamine by organic-free clay minerals (kaolinite and montmorillonite) and by marine sediment studied in laboratory experiments using 14C-labeled compounds. Different adsorption coefficients for the substrates are determined (Monomorillonite: 7.0 mL/g; Kaolinite: < 1mL/g; Marine sediment: 3.5 mL/g). Wang and Lee (1990) also identified that methylated amines can be adsorbed onto marine sediments with adsorption coefficients ranging from 2.4 - 4.7.

Koc values have also been calculated. KOCWIN (v1.68) estimates Koc solely with a QSAR utilizing Molecular Connectivity Index (MCI) resulting in a Koc value of 8.098 for MMA. Another calculation method by Hansch and Leo (1985, details on applied method unknown) estimated a soil adsorption coefficient (Koc) of 12, using a measured log Kow of -0.57 and a recommended regression equation.