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Environmental fate & pathways

Biodegradation in water: screening tests

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Administrative data

Link to relevant study record(s)

Description of key information

When assessing the biodegradation behaviour of cationic surfactants it is important to consider the following facts:
1. Due to the nature of water solubility, bioavailability of the test substance is reduced. Therefore for cationic surfactant instead of an S shape biodegradation curve a more or less straight line may be observed which can be interpreted such that biodegradation is rate limited by the dissolution of the test item.
2. Cationic surfactants may show toxicity to microorganisms at concentration levels normally used for Biodegradation screening tests e.g. the EC50 in inhibition of the respiration testis 64mg/L. Thus, biodegradation of cationic surfactants is often higher at lower test item concentrations which is also more environmentally relevant. Also the conditions in surface water / sediment may enhance biodegradation additionally. Adaptation of the microorganisms is another important parameter for biodegradation.
Therefore, modified ready biodegradability tests using a lower test substance concentration, are relevant when the test substance is known or expected to exert toxicity to the microbial inoculum.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

On the weight of evidence approach (i.e. Key study OECD 301D, Supporting study OECD 301 B), the test substance concluded readily biodegradable. Actually, the borderline previous data (OECD 301B, 59% of biodegradation) has been challenged pursuant to the recent improvement of the ecotoxicological test. Limited bioavailability and toxicity are well reported to be the key point leading to borderline results.