OECD 106: Adsorption – Desorption using a Batch Equilibrium Method

The purpose of this test is to estimate the adsorption/desorption behaviour of a substance on soils.  Therefore, the adsorption (binding of a chemical to surfaces of soils) of a test substance on different soil types will be evaluated. The decrease in concentration when aqueous solutions of the test item are in contact with different soil types at room temperature will be determined. The adsorption/desorption distribution coefficients (Kd, Koc, Kdes) and the Freundlich adsorption/desorption coefficients (KFads, KFdes, KF,OCads, KF,OCdes) will be calculated.

Study Design

Test setup

The test will be carried out with 14C-labelled test substance or non-labelled test substance. Typically, the test will be conducted using five different soil types representative for soils of the West-European area. The test will run using non-sterile or sterile, air-dried and fine sieved soil (≤ 2 mm) and test vessels made of glass. Two replicates will be prepared for each specific soil/solution ratio per sampling time point.  In general, the test samples will be agitated by shaking. Incubation will be accomplished in the dark at a temperature of 20°C.

Course of the test

  • Preliminary Test (Tier 1): In a preliminary test the soil/solution ratios and the amount of test substance adsorbed after 48 h of contact time will be determined. Both, sterile and non-sterile soil, will be used to be able to differentiate between potential biotic degradation and incomplete removal of the test item from the soil matrix.
  • Adsorption Kinetics (Tier 2): The adsorption will be studied by means of adsorption kinetics at a single concentration. Equilibrium time, distribution and adsorption coefficients Kd and KOC will be determined.
  • Desorption Kinetics (Tier 3): In this test phase it will be investigated whether the test item is reversibly or irreversibly adsorbed on soil. Equilibrium time and the desorption coefficient Kdes will be determined.
  • Adsorption /Desorption Isotherms (Tier 3): The influence of the test item concentration on the extent of adsorption/desorption will be investigated. Five concentrations spanning a concentration range of two orders of magnitude will be used.

Analysis of the test substance and transformation products

In case of the 14C-labelled test substance the analytical methods based on LSC and HPLC coupled with UV and radio detection. LC-MS/MS can be carried out as additional analytical method. Non-labelled test substances will be determined using HPLC coupled with UV detection or LC-MS/MS method.

Special test setup

  • A huge number of different soil types can be utilised.
  • Depending on the costumer needs, the test can be conducted using soil provided by the Sponsor.
  • Depending on the costumer needs, the test can be conducted using sewage sludge from waste water treatement plants.


  • Adsorption/desorption distribution coefficients (Kd, Koc, Kdes)
  • Freundlich adsorption/desorption coefficients (KFads, KFdes, KF,OCads, KF,OCdes)

Guidelines and Literature

  • OECD Guideline for the Testing of Chemicals, No. 106, ”Adsorption – Desorption using a Batch Equilibrium Method” adopted January 21, 2000.