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Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Principles of method if other than guideline:
This method corresponds to OECD TG 301 E (Ready biodegradability: Modified OECD-Screening)
GLP compliance:
Oxygen conditions:
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Details on inoculum:
Type: mixed population of aquatic microorgamisms
Origin: secondary effluent from laboratory-scale unit receiving predominantly domestic sewage
Concentration of inoculum: 30 mg/l ss
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
Parameter followed for biodegradation estimation:
DOC removal
Reference substance:
% degradation (DOC removal)
Sampling time:
28 d
Results with reference substance:
Aniline was used as the reference substance and with the same inoculum 100 % degradation was observe. The rate and extent of aniline degradation
fulfilled the validity criteria for the test.
Validity criteria fulfilled:
Aniline was used as the reference substance, present at 20 mg/l DOC. The rate and extent of aniline degradation fulfilled the validity criteria for the test.
Interpretation of results:
under test conditions no biodegradation observed
TCPP is not readily biodegradable (14% degradation after 28 days).
Executive summary:

In a test on ready biodegradability of TCPP conducted according to the EU-method C.4 -D (Determination of the Ready biodegradability: Manometric Respirometry Test) 14 % degradation was observed after 28 days (Bayer AG, 1991).

Description of key information

OECD 301E (equiv.) (Bayer, 1991): 14% degradation (28d) - not redily biodegradable
EU C.6 (prolonged) (Van Togt & Van Ginkel, 2002): 13% degradation (28d), 71% degradation (84d) - not readily biodegradable
OECD 302A (Van Togt & Van Ginkel, 2001): 95% degradation (64d)

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:

Additional information

Bayer AG (1991) conducted a study in accordance with OECD 301E, where the ready biodegradability potential was assessed over a 28-day period.  The substance was shown to biodegrade by 14 % in 28-days indicating that the substance is not readily biodegradable.  Van Togt & Van Ginkel (2002) conducted a prolonged closed bottle test using domestic activated sludge as an inoculumm, with an initial test substance concentration of 4 mg/L.  The substance was shown to degrade by 13 % in 28-days, which was consistent with the OECD 301E study.  However, prolongation of the study to 84 days showed that the substance degraded by 71 %, although it should be noted that no degradation was observed in this study for the first three weeks.  Finally, Van Ginkel & Stroo (2001) assessed the potential inherent biodegradability of the substance conducting a modified SCAS test in accordance with OECD 302 A.  The study was conducted with secondary activated sludge, with a total duration of 64-days and an initial test item concentration of 30 mg/L.  The test item was shown to degrade by 95 % in 64-days, but required an acclimation period of ~3 weeks prior to the onset of rapid degradation of the substance.


The ready biodegradability study (Bayer AG, 1991) and modified MITI test (Van Ginkel & Stroo, 2001), indicate that the substance is not readily biodegradable, nor inherently biodegradable.  Whilst the prolonged closed bottle test (Van Togt & Van Ginkel, 2002) indicate potential for the substance to degrade (71 % degradation after 84-days), these data can not be used to refine degradation constants for exposure assessment, nor confirming that the substance is not potentially P/vP.  


According to the criteria set for P/vP assessment (ECHA Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11, 2017), negative results in ready biodegradability tests can be supported with inherent biodegradability tests or enhanced screening tests to investigate potential persistence in the environment.  Van Ginkel & Stroo (2001) showed that the substance does not meet the criteria of 70% mineralization (O2 uptake) within 14 days, and the log phase should be no longer than 3 days required to conclude that the substance will not persist in the environment from an inherent biodegradability test.  Similarly, Van Togt and Van Ginkel (2002) failed to show that the substance meets the criteria set for enhanced screening tests required to conclude that the substance will not persist in the environment.  Whilst the 60 % mineralisation target was met within 60-days, strong evidence of inoculum adaptation was present, with 0 % degradation shown for the first 21-days, followed by degradation to 71 % by day 84.  Evidence of inoculum adaptation as seen in this study, precludes the data from being used to conclude that the substance is not p/vP (ECHA Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7b, 2017).


The existing data therefore indicate that the substance is potentially P/vP.