OECD 121 – Adsorption Coefficient using HPLC

OECD 121 estimates the adsorption coefficient on soil and sewage sludge using high-performance liquid chromatography (HPLC).


The adsorption coefficient (Koc) determines the tendency of a chemical to bind to soils or sewage sludge. The binding capacity of a chemical on organic matter of soil and sewage sludge allows comparisons to be made between different chemicals through their adsorption behavior.

The OECD 121 test determines the Koc of a sample using high-performance liquid chromatography (HPLC).  The absorption coefficient can be estimated through other analytical OECD test measurements, including water solubility (OECD 105) and the octanol/water partition coefficient (OECD 117).

Test methods that determine the absorption coefficient on soil and sewage sludge are generally requested for pesticide testing.  Pesticide testing is required for pesticide registration or reregistration and encompasses a variety of test types.  Generally speaking, pesticides undergo analytical testing to determine physical and chemical properties like adsorption coefficient, water solubility, and partition coefficient.

Pesticides are also generally required to undergo a variety of Toxicology, Ecological, and Environmental fate testing.  US EPA outlines many of these requirements in the  40 CFR Part 158, Data Requirements for Registration.  Determining a chemical’s adsorption coefficient is generally performed to meet the requirements for Mobility studies of the test substance or chemical.

An important part of a pesticide registration is evaluating the chemical pesticide and determining its effects on the surrounding environment.  Determining the absorption coefficient of a chemical substance provides information on how a chemical substance will behave in the environment when in contact with soil or sewage sludge.  The absorption coefficient, in general, determines important information on a chemical’s behavior.

For more information on Analytical testing and OECD 121, contact our analytical laboratory at 847-483-9950 or info@situtest.com.