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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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biodegradation in water: simulation testing on ultimate degradation in surface water
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is highly insoluble in water
Justification for type of information:
According to the REACH Annex IX, Section 9.2, further biotic degradation testing in appropriate compartment shall be performed to investigate further the degradation of the substance and its degradation product to conclude on the persistency of the tested substance.
The following known critical properties of the substances of the category have been considered for simulation testing strategy:
- Mobility: each substance of the category have a predicted Koc values>>1,000,000 mL/g (KOCWin v2.00; EPISuite v 4.11) indicating substances will have a very high affinity to bind to organic matter.
- n-octanol water partition coefficient – each of the substances of the category have predicted or experimental log KOW values >> 4.5, reinforcing the hypothesis that the substances will have a high affinity to bind to organic matter.
- Water solubility –each substance of the category has a very low water solubility <20 µg/L.
- Ready biodegradation – screening tests (OECD 301 and 302) confirm that the substances of the category do not fulfil the ready biodegradability criteria.
Figure R.11-3 outlines the testing strategy for persistence assessment (ECHA, R.11, June 2017) where the guidance indicates that testing should begin with an OECD Test Guideline (TG) 309. Based on the profile described above it would be more appropriate to begin simulation tests in compartments where the substances are most likely to have the potential to persist and accumulate in the environment i.e., soil or sediment. In addition, the conduct of the OECD-TG 309 would have significant practical challenges owing to the substance properties that could jeopardise the validity of the test and restrict the amount of useful data generated for use in the risk assessment:
Adsorption – test substances with profiles, such as those described above, will bind to apparatus used to incubate the test system. This would be a particular challenge in a pelagic OECD-TG 309. In a suspended sediment OECD-TG 309 the test substance may preferentially bind to the organic matter versus the testing apparatus. It is unlikely that quantifiable residues would be recovered from the surface water.
• Mass balance – in either case (pelagic or suspended sediment), the substance will rapidly partition from the surface water. In an OECD-TG 309 this could lead to low mass balance if the test item is non-recoverable from the test apparatus/ storage containers. The validity of the study would then be brought into question.
• Transformation products– the quality of data generated from an OECD-TG 309 would be more limited than that generated from an OECD-TG 307 or OECD-TG 308. Identification of potential metabolites could be limited as the upper concentration for testing would be restricted <20 µg/L. If the test substance rapidly partitions, as expected, then recoveries in the surface water will likely be Based on the points described above, it is proposed to waive simulation testing on ultimate degradation in surface water (OECD-TG 309) and start simulation testing in soil (OECD-TG 307 Testing Proposal; 2022).

Data source

Materials and methods

Results and discussion

Transformation products:

Applicant's summary and conclusion