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adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: This study is a publication which meets basic scientific principles.

Data source

Reference Type:
Biodegradation kinetics and sorption reactions of three differently charged amino acids
Jones D.L. and Hodge A.
Bibliographic source:
Soil Biology and Biochemistry 31 (1999) 1331-1342

Materials and methods

Test guideline
no guideline followed
Principles of method if other than guideline:
To determine the amount of amino acid sorption to soil's solid phase, 0.5 g of soil was placed in polypropylene tubes and 5 mL of a uniformly 14C labelled lysine (specific activity = 12 GBq mmol-1) was added to the soil to give concentrations ranging from 0.001 to 10 mM and total activity of 0.2 kBq. The soils were then orbitally shaken at 300 rev/min for 5 min at 15C, centrifuged ( 15 000 g, 15 min) and the amount of 14C in the supernatant solution determined by liquid scintillation counting (Wallac 1409 counter, Wallac Optiphase 3 scintillation fluid; EG&G Ltd., Milton Keynes, UK). Due to large soil-to-solution ratio and rapidity of the sorption studies, substrate biodegradation was minimal (=< 4%) during the sorption procedure. This was confirmed by repeating some of the isotherms with soil fumigated with CHCl3 for 24 h or by performing the sorption isotherms in the presence of 10 mM HgCl2.
GLP compliance:
not specified
Type of method:
batch equilibrium method

Test material

Constituent 1
Reference substance name:
EC Number:
EC Name:
Cas Number:
Details on test material:
Uniformly 14-C labelled lysine with specific activity of 12 GBq/mmol

Study design

Test temperature:

Batch equilibrium or other method

Analytical monitoring:
Details on sampling:
See details on test conditions.
Details on matrix:
Soil: 85.1% sand (2000-63 µm), 6.4% silt (63-2 µm), 8.5% clay (<2µm). pH-H2O 7.5, pH-CaCl2 6.8, Organic C 1.41%. Texture: loamy sand.
Details on test conditions:
0.5 g soil + 5 mL testsubstance solution (solvent not specified). Initial lysine concentrations ranged from 0.001 mM to 10 mM (6 concentration levels tested).
Equilibration for 5 min at 15°C on shaker.
Supernatant removed after centrifugation for total radioactivity measurement.
Computational methods:
Amount adsorbed calculated by difference between initial radioactivity in solution and radioactivity left in solution after adsorption phase.
Langmuir Isotherms were fitted to the data.
A Koc values was not reported but was calculated by the registrant based on formula Kd = Cads/Ceq and Koc = Kd/%oc for an equilibrium concentration of 10 µM (1.8 mg/L).

Results and discussion

Adsorption coefficient
88 936
15 °C
% Org. carbon:

Results: Batch equilibrium or other method

Adsorption and desorption constants:
Koc = 88936 L/kg (Kom = 51587 L/kg)
Recovery of test material:
Not reported. It was stated that lysine was stable during the experiment (because of a contact time of only 5 minutes). This was verified and confirme by performing isotherms with sterilised soils (results not shown).
Concentration of test substance at end of adsorption equilibration period:
At a starting concentration of 10 mM the equilibrium concentration was approximately 45 µM (taken from graph)
Concentration of test substance at end of desorption equilibration period:
Desorption not performed

Any other information on results incl. tables

The equilibrium period was only 5 minutes. It was not demonstrated whether equilibrium was achieved within this period. In general equilibrium is rapidly achieved in batch adsorption experiments. Lysine, being positively charged, is expected to adsorb very rapid to soil and therefore it is expected that the equilibrium conditions will be achieved or at least closely approached within a soil:solution contact time of 5 minutes. The calculated Koc value is considered acceptable (and in case equilibrium would not have been completely achieved it would only become larger).

Applicant's summary and conclusion

Validity criteria fulfilled:
Koc for lysine is 88936 L/kg (Kom 51587 L/kg).
Executive summary:

The adsorption coefficient of lysine was determined in a batch equilibrium sorption experiment (loamy sand soil, pH-H2O 7.5 and %oc 1.41). Initial concentrations ranged from 0.001 mM to 10 mM. The soil:solution ratio was 1:10 w/w and adsorption took place at 15°C for a contact time of 5 minutes. Following the adsorption phase, lysine remaining in the solution was determined by a total radioactivity measurement. Amount adsorbed was calculated by the difference between initially added lysine and lysine remaining in solution after the adsorption phase. The adsorption isotherm could be described by the Langmuir isotherm. At an equilibrium concentration of 10 µM (1.8 mg/L), a Koc of 88936 L/kg was determined (Kom 51587 L/kg).