A review of the applicability of the screening test for soil adsorption potential, and recommendations for expansion: summary
Published 10 January 2025
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1. Chief Scientist’s Group report summary
This project explored the potential for adapting a standardised test method to provide a more accurate measure of how strongly a test substance may interact with (and therefore move through) soils and sediments.
1.1 Background
It is important to understand how easily substances can pass through soils and sediments because this can help indicate how likely they are to contaminate water bodies. This “mobility” property is currently being considered as part of a new hazard category under the United Nations Globally Harmonised System of Classification and Labelling of Chemicals (UN GHS).
The standard screening method to measure how strongly substances interact with soils and sediments is the Organisation for Economic Co-operation and Development (OECD) test guideline (TG) 121. It uses an analytical technique called high-performance liquid chromatography (HPLC) to measure the time taken for a test substance in a solvent (the liquid phase) to pass through a synthetic solid material (the stationary phase). Substances that bind more strongly to the stationary phase take longer to pass through and are considered likely to bind more strongly to soils and sediments (and therefore less likely to pass through them). The strength of binding is represented by the organic carbon normalised adsorption coefficient (log KOC), which is determined by comparing the retention times of the test substance and a series of substances of known log KOC values.
The stationary phase of the OECD TG 121 method does not capture all of the interactions that may occur in soils or sediments for some substances, meaning that the measured log KOC value may not be a true reflection of mobility. Given global interest in a new hazard type that aims to characterise mobility for the protection of water resources, it is important to consider whether existing test methods are fit for purpose.
1.2 Approach
A search of published academic literature was performed to identify the main interactions that occur for substances in soils and sediments. The findings were used to summarise which potential interactions are represented by the stationary phase used in OECD TG 121. Alternative materials that could be used as the stationary phase were identified to see if the range of interactions represented could be expanded within an HPLC method.
1.3 Results
The stationary phase used in OECD TG 121 only adequately represents two of the four main types of interaction that may occur for substances in soils and sediments. This confirms that the log KOC values determined using OECD TG 121 may not represent the mobility of substances in soils and sediments where other interactions are more dominant.
Several alternative solid phases were considered that may better represent these other interactions. The most promising materials for further investigation were identified and recommendations made for practical testing to assess their suitability. The project concludes that development of an additional HPLC test method which uses different stationary phases may be possible.
1.4 Publication details
This summary relates to information from the following project:
- Title: A review of the applicability of the screening test for soil adsorption potential, and recommendations for expansion
- Project manager: Richard Gibson, Chemicals Assessment Unit, Chief Scientist’s Group
- Contractor: WCA Environment Limited, Brunel House, Volunteer Way, Faringdon, Oxfordshire, SN7 7YR
This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.
Enquiries: research@environment-agency.gov.uk.
© Environment Agency