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OECD 308 Updates - Implications for Chemical Analysis
OECD 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
New definitions and additional analytics have been incorporated in the OECD 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems) workflow, which is especially relevant to chemical companies interested in non-extractable residues (NERs) in these studies.
Charles River Laboratories (CRL) Den Bosch added several of these workflow options from the updated guideline (ECHA Chapter R11, Dec 2023) to characterize and identify the non-extractable residues and give some more details about the degradation route of the test materials.
New Classification of Non-extractable Residues
The classification of NERs requires characterization of NER items that can remobilize and items that will remain attached to the sediment after harsh extractions. The aim of the new workflow is to identify NERs to understand if parent test material will remain.
In the new classification system, NERs are categorized in three classes:
- NERs Type I are strongly adsorbed or physically entrapped in the matrix and have the potential to be remobilised.
- NERs Type II are covalently bound to the matrix in surface water, soils or sediments and are considered to have low remobilisation rates. Unless there are indications from available literature or monitoring data regarding their potential remobilisation, covalently bound residues may be regarded as irreversibly bound.
- NERs Type III (bioNER) are incorporated into biomass and result from the anabolic formation of biomolecules (amino acids, phospholipids, and other biomass compounds) from the degradation products of the parent substance. NERs Type III are considered to be of no concern.
The following changes are implemented in the new workflow:
NER Identification
The newly proposed workflow in Appendix R.11-3 (ECHA Chapter R11) consists of two steps with multiple techniques proposed. The first step distinguishes extractable fractions and non-extractable residues, the latter indicates if the substance or its transformation/degradation products remain in the matrix (soil, sediment, suspended matter). If the extractable fraction contains a significant amount of parent, this would then be used to assess the DT50 of a test material which indicates if a test material is persistent or even very persistent.The second step helps to categorize NERs into those that would potentially remobilise (NER type I) and those that would remain in the matrix (NER type II and NER Type III). If it is not possible to identify the test material in NERs Type I, the applied radioactivity will count as non-degraded parent and may also influence the derivation of the DT50 value.
Both steps outlined above have now been incorporated into the workflow of the OECD 308 within Charles River. For the first step, a combination of organic solvent extractions and the use of an Accelerated Solvent Extractor (ASE) are used. The second step will be performed by an EDTA extraction to distinguish NERs Type I and Type II. Overall, this gives a more representative picture of the degradation route of the test material as desired by authorities.
- Inclusion of Sterile Controls
In simulation tests, it is important to differentiate degradation and disappearance of the test substance due to other dissipation processes. An important advantage of using sterile controls in degradation studies is that it helps estimate to what extent abiotic processes (abiotic degradation and non-degradative dissipation) impact the disappearance of the substance. In addition, sterile controls can be helpful in verifying the exposure level of the test material in the test system and for the determination of a mass balance. To present a more complete determination of the mass balance and degradation route sterile controls are now used in all types of environmental fate studies.
Learn more about how Charles River can help plan and execute a testing plan for your chemical compounds which is both efficient and effective.