OECD 106: Adsorption – Desorption Using a Batch Equilibrium Method
OECD 106 estimates the adsorption/desorption behavior of a substance on different soil types.
Test methods that measure adsorption/desorption are useful for obtaining information on the behavior of chemicals in the soil, water and air. These methods can be used in the prediction or estimation of the availability of a chemical for degradation, transformation and uptake by organisms, leaching through the soil profile, volatility from soil, and run-off from land surfaces into bodies of water.
The OECD 106 Adsorption/desorption test method is useful for generating essential information on the mobility of chemicals and their distribution in the soil, water and air compartments of our biosphere.
The aim of the OECD 106 test method is to determine the sorption value which can be used to predict partitioning under a variety of environmental conditions. The test is evaluates the adsorption of a chemical on different soil types that vary in organic carbon content, clay content, soil texture, and pH. Different types of soil are used to model how the substance will behave with naturally occurring soils. The OECD 106 method includes three tiers:
- Tier 1: Preliminary step determines soil/solution ratio, equilibration time for adsorption, amount of test substance adsorbed at equilibrium, adsorption of the test substance on the surfaces of the test vessels, and stability of the test substance during the test period. (1)
- Tier 2: Screening test: the adsorption is studied in five different soil types by means of adsorption kinetics at a single concentration and determination of distribution coefficients Kd and Koc.(1)
- Tier 3: Determination of adsorption isotherms to determine the influence of concentration on the extent of adsorption on soils. (1)
Before carrying out a test for adsorption-desorption, the following information on the test substance should be available:
- solubility in water (OECD 105)
- vapour pressure (OECD 104)
- hydrolysis as a function of pH (OECD 111)
- n-octanol/water partition coefficient (OECD 107 and 117)
- ready biodegradability (OECD 301)
- pKa of ionizable substances
- direct photolysis in water and photodegradation on soil.
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