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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
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP guideline study. Activated sludge originated from a laboratory scale sewage plant treating municipal sewage.
according to
OECD Guideline 301 A (Ready Biodegradability: DOC Die Away Test)
GLP compliance:
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: activated sludge from laboratory scale sewage plant treating domestic sewage
- Preparation of inoculum for exposure: The suitable aliquot of the activated sludge suspension was sieved by a finely woven mesh with a mesh size about 0.45 µm.
- Concentration of sludge: 30 mg/L dry weight
Duration of test (contact time):
28 d
Initial conc.:
64.1 mg/L
Based on:
test mat.
Initial conc.:
20 mg/L
Based on:
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
- Composition of medium: according to guideline
- Additional substrate: an inorganic nutrient salt medium was added.
- Solubilising agent: No solubilising agent was used.
- Test temperature: 20 - 25 °C

- Culturing apparatus: The DOC Die Away test was performed in flasks according to the guideline.
- Number of culture flasks/concentration: 2
- Number of blank control flasks: 2
- Number of inhibition control flasks: 1
- Number of positive control flaks: 1
- Number of adsorption control flasks: 1
- Measuring equipment: Samples for the DOC-analysis were performed as repeat determination, using a TOC-analyzer equipped with an auto sampler (Shimadzu TOC-500).

- Sampling method: For preparation of the test assays, first the required volume of demineralized water and the solutions of mineral medium were dosed to the test vessels. For addition of the test- and reference substance aqueous stock solutions with suitable concentrations were prepared.
The content of DOC of the reference substance was calculated as theoretical organic carbon value (ThOC) and also used for the calculation of the required aliquot. The test assay of adsorption control (AC) was prepared in the same way. Aliquots of the prepared inoculum suspension were added to all test vessels (exceptional PC-assay): to adjust a concentration of activated sludge of 30 mg/L dry weight. The sampling in the AC test assay was performed before adding inoculum.
- Sampling frequency: daily.
- Sterility check if applicable: For avoidance of bacterial grow the assay was inhibited by adding of 1 mL mercury chloride solution on day 14 in the test medium.

- Inoculum blank: 2
- Abiotic sterile control: 1
- Toxicity control: 1
- Other: Toxicity control: 1
Reference substance:
benzoic acid, sodium salt
% degradation (DOC removal)
< 10
Sampling time:
28 d
Details on results:
The test substance did not show inhibition of microorganisms in a toxicity control. No elimination of the test substance was observed in the treatments. thus, the test substance is considered to be neither readily nor inherently biodegradable.
Results with reference substance:
Total elimination was observed at day 7.
Validity criteria fulfilled:
Interpretation of results:
under test conditions no biodegradation observed

Description of key information

Not readily/inherently biodegradable: < 10% in 28 days (OECD 301A)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

One study investigating the ready biodegradability of 3-(amidinothio)propionic acid (CAS 5398-29-8) is available. The study was performed according to GLP and OECD guideline 301A (BASF 1995). Non-adapted activated sludge from a laboratory scale sewage plant treating domestic sewage was used as inoculum. DOC removal was measured over a test period of 28 days. No DOC removal was observed throughout the test period. Thus, the test substance is considered to be neither readily nor inherently biodegradable according to OECD criteria.