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Environmental fate & pathways

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:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
OECD 301F GLP study (all validity criteria can not be confirmed)
equivalent or similar to guideline
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
theorical oxygen demand: 1990mgO2/g
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Reference substance:
Preliminary study:
Toxicity on activated sludge: EC 50=2950 mg/l
Key result
% degradation (O2 consumption)
Sampling time:
28 d
Remarks on result:
other: Not readily biodegradable
Results with reference substance:
Anilin: 95% of biodegradation after 28d

not readily biodegradable

Validity criteria fulfilled:
not specified
The oxygen uptake of the inoculum blank is well normally 20-30 mg 02/l. No details on pH values and reference substance data.
Interpretation of results:
not readily biodegradable
chlorobenzene is not readily biodegradable.
Executive summary:

Bayer AG (1992).

A test on biodegradation following OECD Guideline 301F with activated sludge exposed to 100 mg chlorobenzene/L under aerobic conditions for 28 days showed that chlorobenzene is not readily biodegradable.

Description of key information

15% of biodegradation after 28 days ; OECD 301F; Bayer (1992)

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable

Additional information

A test on biodegradation following OECD Guideline 301F with activated sludge exposed to 100 mg chlorobenzene/L under aerobic conditions for 28 days showed that chlorobenzene is not readily biodegradable (BAYER AG,1992).

This study is supported by two non-GLP OECD 301D studies (Picone & Geerts, 2022; Bayer, 1973) showing primary degradation of Chlorobenzene reaching up to 54% but always below the level of 60% of readily biodegradability. Biodegradation above 20% of theoretical (measured BOD, COD removal or COD) may be regarded as evidence of inherent, primary biodegradability. Based on these results from OECD 301D tests, chlorobenzene could be considered as potentially inherently biodegradable. 

In literature a wide variety of bacterial strains is described that can use chlorobenzenes as sole source of carbon and energy for growth. In most of these studies also sound evidence is provided for the mineralization of chlorobenzenes (Field and Sierra-Alvarez, 2008).

The reason why a ready biodegradation (mineralization) was not demonstrated (yet) in ready biodegradation screening tests is most likely a combination of:
- the hampered biodegradation at the start of the tests caused by toxicity of the relative high initial test substance concentration used in ready biodegradation tests and

- possible losses of the test substance during the biodegradation measurements in ready biodegradation tests.
The repetitive measurements in the triplicate closed bottles used in the study from Picone & Geerts (2022) could be the reason for test substance losses and biodegradation curves leveling of below 60%. 

A biodegradation study of the HOECHST AG (activated sludge, industrial, non adapted, respirometry) showed a degradation of >90% after 15 days and 70% after 10 days. Because the original reference is not available the results/study is not reliable.
Chlorbenzene can be degradaded aerobically by adapted microorganisms in water.


Field JA, Sierra-Alvarez R (2008) Microbial degradation of chlorinated benzenes. Review paper. Biodegradation 19, 463-480.