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OECD TG 122

Nano-Test® > Research > Standards > OECD TG 122

OECD TG 122 is a standard within the OECD Test Guidelines for the Testing of Chemicals, Section 1 (Physicochemical Properties), which pertains to the estimation of the adsorption coefficient (Koc) in soil and sewage sludge using high-performance liquid chromatography (HPLC). This is not a direct experimental measurement of adsorption, but rather a screening and estimation method.

The adsorption coefficient (Kd) describes the distribution of a substance between a solid matrix, such as soil or sewage sludge, and the aqueous phase. The organic-carbon-normalized adsorption coefficient (Koc) is calculated by dividing the Kd value by the organic carbon content of the matrix and serves as a fundamental parameter for assessing the mobility of the substance in soil. The OECD Test Guideline 122 is based on the principle of not measuring the Koc value directly using the batch equilibrium method (OECD TG 106), but rather estimating it based on the correlation between the retention behavior in the HPLC system and the Koc value.

The basic principle of the test is as follows:

  • The test substance and reference substances with known Koc values are analyzed using a standardized HPLC system.
  • The capacity factor (k′) is calculated for each substance:

k′ = (tR − t0) / t0

Here, tR is the retention time and t0 is the time for the void volume (the component that is not retained).

  • A regression relationship is established between the known log Koc values of the reference substances and the measured log k′ values.
  • The measured k′ value of the test compound is substituted into this calibration equation to estimate the log Koc value and, subsequently, the Koc value.

The system components frequently used in this process are:

Pillar:

  • C18 (octadecyl)- or cyanopropyl-coated analytical columns
  • The particle size of the column, its dimensions, and the type of coated phase must be kept constant and specified

Mobile phase:

  • Water/methanol or water/acetonitrile mixtures
  • Since the composition and pH of the mobile phase directly influence retention behavior, they must be controlled and specified

Reference substances:

  • Substances for which Koc values are known from reliable sources and which are chemically similar to the test substance
  • The log Koc values of the reference substances should be selected so that they cover the expected range of the test substance

Detection:

  • UV-VIS detector, diode array detector (DAD), or other suitable detectors
  • Measurement of the test substance and the reference substances at an appropriate wavelength and with sufficient sensitivity

The basic parameters specified in the study are:

  • log Koc and Koc (L/kg)
  • Capacity factor (k′) and retention times (tR, t0)
  • Column used, mobile phase composition, and pH
  • Reference substances and their known log Koc values
  • Regression equation, correlation coefficient (r²), and scope of validity
  • Measured temperature
  • Data on Measurement Uncertainty and Repeatability

Why is it performed?

OECD TG 122 is being conducted for the following scientific and regulatory purposes:

  • Assessment of Mobility in Soil: The Koc value is a fundamental indicator of a substance's potential to be leached from the soil and transported into groundwater
  • Assessment of Environmental Fate: Adsorption behavior determines the distribution of the substance among soil, sediment, and water
  • Preliminary Assessment for Screening Purposes: Provides a quick and cost-effective preliminary estimate before resorting to the batch equilibrium method (TG 106)
  • Support for regulatory submissions: Used in environmental impact assessments under REACH for plant protection products, biocides, and pharmaceuticals
  • Filling data gaps: Provides estimates for substances for which no experimental Koc data are available
  • Prioritization: Is this an appropriate method for screening a large number of substances and prioritizing risks?
  • Modeling input: Used as the Koc parameter in environmental fate and transport models
  • Quality Control: Monitoring the Consistency of the Adsorption Behavior of Substances in Production Processes

OECD TG 122 provides estimates rather than direct measurements. The results should be verified using direct measurement methods, such as the OECD TG 106 batch equilibrium method, particularly when they are critical to regulatory decision-making processes. The estimates should be interpreted taking into account the chemical structure of the substance, its ionization state, and the matrix properties.

As part of our nano-testing services, we conduct Koc estimation work in accordance with OECD TG 122 with scientific rigor, utilizing our accredited laboratory infrastructure and our quality management system. Our scope of services includes the following:

Method Selection and Validation

Assessment of the applicability of OECD TG 122 based on the chemical properties of the test substance (polarity, ionization, molecular size)

Selection of a suitable column (C18 or cyanopropyl) and a suitable mobile phase system

Selection of reference substances with known Koc values that cover the expected range of the test substance

Plotting the calibration curve, determining the regression equation and the r² value

Validation of the method: linearity, accuracy, repeatability, and inter-repeatability; evaluation and reporting of measurement uncertainty; documentation of method-specific limitations and conditions of use

For your Koc estimates under OECD TG 122, you can contact Nano-Test to obtain information on the applicability of the method, the selection of reference substances, the validation of the HPLC system, sample acceptance criteria, the testing schedule, and reporting procedures.

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