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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Available data include inherent biodegradation tests (Zahn-Wellens test, OECD302B) and a ready biodegradability test according to the DOC Die-Away test (OECD301A). The latter study is considered reliable (Klimisch 1) and is used as key study for this endpoint. All information together justifies the conclusion that the substance is ultimately and inherently biodegradable, not fulfilling specific criteria.
The results of the BASF study (OECD 301A) indicates that NNMO is not readily biodegradable. The results of the Zahn-Wellens tests (OECD302B) with unadapted and adapted sludge reported by Meister and Wechsler (1998) indicate that NMMO is inherently biodegradable, not fulfilling specific criteria, but that adaptation of the sludge is required for efficient breakdown. Additional experiments indicated that the substance is ultimately biodegradable and no persistent breakdown products are formed. This study is considered reliable (Klimisch 2) and is used as key study for this endpoint.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

The reliable key study determined the ready biodegradability of NMMO in a DOC Die-away test according to OECD 301A guidelines and in the presence of activated sewage sludge with 30 mg/L suspended solids. The test period was 28 days; after 28 days on average < 10% biodegradation was observed. The results show that the substance is not readily biodegradable.

Significant biodegradation however was observed in an OECD 302B test (BASF AG 2001) (ultimate biodegradability of 90 -100%) concluding that the substance is inherently biodegradable.

Meister and Wechsler (1998) thoroughly investigated the biodegradation of NMMO, NMM and morpholine using a variety of experiments, including guideline studies (OECD302B, Zahn-Wellens test for inherent biodegradation), lab-scale and pilot-scale experiments. This study was considered reliable (Klimisch 2). A first Zahn-Wellens test with unadapted sludge from a WWTP with high load and only short-living sludge organisms (sludge age 2-3 days) indicated < 20% degradation (based on COD) in 28 days. However, a second Zahn-Wellens test with adapted sludge from a WWTP with both short- and long-living sludge organisms (sludge age >= 14 days) indicated > 90% degradation (based on test material analysis) within 21 days. Based on this study NMMO can be considered inherently biodegradable without fulfilling specific criteria. The other experiments (lab-scale, pilot-scale) indicated that NMMO is ultimately biodegradable, and adaptation of the sludge speeds up the degradation. For successful adaptation a high sludge age is recommended, indicating that slowly-reproducing (long-living) sludge organisms are more efficient degraders of the substance. The degradation takes place in several steps. First, NMMO is reduced to NMM. The next step (rate-limiting) is the demethylation of NMMO to morpholine. This step is followed by much faster ring cleavage and further degradation.

Additionally, these authors investigated degradation of NMMO under anaerobic conditions. Hereto two yeast species (Saccharomyces carlbergensis and Saccharomyces cerevisiae) were exposed to the substance during 14 days. Mainly Saccharomyces carlbergensis significantly degraded NMMO to NMM (complete degradation to NMM), indicating that the substance is also biodegradable under anaerobic conditions. However, no further breakdown of NMM occurred in these experiments and no further experimentation was undertaken.