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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
according to
Guideline:
ISO 14593:1999 (Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium - Method by analysis of inorganic carbon in sealed vessels (CO2 headspace test))
Deviations:
not specified
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Deviations:
not specified
GLP compliance:
no
Remarks:
The study was conducted prior to 01 June 2008.
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): A mixed population of activated sewage sludge micro-organisms (Test System) was obtained from the secondary treatment stage of the sewage treatment plant at Villette (Geneva, Switzerland)), which treats predominantly domestic sewage.
- Storage conditions: See pretreatment field.
- Storage length: < 1 week
- Preparation of inoculum for exposure:
- Pretreatment: The sample of activated sewage sludge was maintained on continuous aeration upon receipt. A sample of the activated sewage sludge was filtered through a coarse filter paper. The filtrate was centrifuged/washed twice with deionised water, resuspended at pH 6.5 and then oxygenated (stream of pure oxygen) for 6 h to reduce the carbon load (organic and inorganic). The final inoculum concentration in test bottles was 20 mg/L dry weight activated sludge solids.
- Concentration of sludge: The sludge was diluted in the test bottles to 20 mg DW/L.
Duration of test (contact time):
28 d
Initial conc.:
25 mg/L
Based on:
test mat.
Remarks:
18.75 mg C/L
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: 10 mL of Solution A [KH2PO4: 8.50 g/L; K2HPO4: 21.75g/L; Na2HPO4,2H2O: 33.40 g/L; NH4Cl: 0.50 g/L]; 1 mL of Solution B [CaCl2,2H2O: 27.50 g/L]; 1 mL of Solution C [MgSO4,7H2O: 22.50 g/L]; 1 mL of Solution D [FeCl3,6H2O: 0.25 g/L] and purified water diluted to 1 L.
- Solubilising agent (type and concentration if used): None.
- Test temperature: 24 ±2 °C
- pH: Starting pH 7.4
- pH adjusted: N
- Aeration of dilution water: Not reported
- Suspended solids concentration: 20 mg/L dry weight
- Continuous darkness: No. The test was conducted in diffuse light.

TEST SYSTEM
- Culturing apparatus: 5500 mL glass flasks with continuous stirring (fill volume ca. 2000 mL)
- Number of culture flasks/concentration: In duplicate (test item); In duplicate (Inoculum blank); duplicate flasks (reference item) ; N/A (Abiotic Sterile Control and toxicity control)
- Method used to create aerobic conditions: Gas tight syringe/teflon septum.
- Measuring equipment: Measuring the increase of IC (Inorganic Carbon) in the headspace and the liquid phase of each vessel by gas-tight syringe and needle through the teflon septum (10 ml) and direct injection on the TOC (Total Organic Carbon) analyser. The sampling of the liquid phase was done through the bottom of the vessel and the sample was filtered on a 0.2 m filter prior to analysis. Analysis conducted in triplicate.

SAMPLING
- Sampling frequency: Every three or four days to day 28.
- Sampling method: Measuring the increase of IC (Inorganic Carbon) in the headspace and the liquid phase of each vessel by gas-tight syringe and needle through the teflon septum (10 ml) and direct injection on the TOC (Total Organic Carbon) analyser. The sampling of the liquid phase was done through the bottom of the vessel and the sample was filtered on a 0.2 m filter prior to analysis. Analysis conducted in triplicate.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes.
- Abiotic sterile control: No.
- Toxicity control: No.
- Other: Positive reference control (Methyl dihydrojasmonate).
Reference substance:
other: methyl dihydrojasmonate
Remarks:
25.2 mg/L or 17.37 mg C/L
Parameter:
% degradation (inorg. C analysis)
Value:
82.19
Sampling time:
28 d
Details on results:
The 10-day window criteria may have been met, but due to TOC analyser failure a reading was not taken and therefore was considered not met. Although the 10-d window need not apply.

Applicant assessment indicates: The test item was biodegraded by 82.19% at day 28 in the CO2 evolution test. The multi-constituent test substance is therefore classified as readily biodegradable. The 10-day window that can be applied to Ready Biodegradability Tests, where 60% (O2 consumption or CO2 evolution) or 70% (dissolved carbon generation) biodegradation must be achieved following the attainment of 10 % biodegradation, is not applied to multi-constituent substances consisting of structurally similar constituents (OECD, 2006).
References:
1. OECD (2006), Introduction to the section of the OECD Guidelines for Testing of Chemicals on Degradation and Accumulation
2. GHS revision 4 (2011), Globally harmonized system of classification and labelling of chemicals (GHS). Chapter 4.1. Hazardous to the Aquatic Environment. United Nations, 2011
Results with reference substance:
The reference item attained 65% degradation at 5 days and 79.9% degradation after 28 days thereby confirming the suitability of the inoculum and test conditions.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item mean biodegradation in duplicate was 82.19 % at day 28. 10-d window does not apply to multi-constituent substances consisting of structurally similar constituents (OECD, 2006).
Executive summary:

The ready biodegradability test was carried out according to ISO 14593 equivalent or similar to OECD TG 310 guideline. The test item, at a concentration of 25 mg/L was exposed in duplicate to activated sewage sludge micro-organisms obtained from the secondary treatment stage of the sewage treatment which treats predominantly domestic sewage (Villette: Geneva, Switzerland) with culture medium in sealed culture vessels in diffused light at 24°C ± 2°C for 28 days. The sludge was diluted in the test bottles to 20 mg DW/L. The degradation of the test item was assessed by the regular measurement of inorganic carbon (IC) production on days 0 and 28. This was achieved by measurement of the IC (Inorganic Carbon) in the headspace and the liquid phase of each vessel by gas-tight syringe and needle through the teflon septum (10 ml) and direct injection on the TOC (Total Organic Carbon) analyser. The sampling of the liquid phase was done through the bottom of the vessel and the sample was filtered on a 0.2 m filter prior to analysis. Analysis conducted in triplicate. The reference item attained 65% degradation after 5 days thereby confirming the suitability of the inoculum and test conditions. The mean biodegradation for duplicate test flasks at 28 days for the test item was 82.19%. It was considered the 10-day window was not met due to technical issue with the TOC analyser. However, the 10-d window does not apply to multi-constituent substances consisting of structurally similar constituents (OECD, 2006). Under the conditions of the study, test item is considered as readily biodegradable.

Description of key information

Biodegradation: readily biodegradable, mean biodegradation 82.19% (28-days, 10-day window not met). 10-day window not applicable to multi-constituent substances consisting of structurally similar constituents (OECD, 2006); eq. or similar to OECD TG 310, 2003

 

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

Key Study: eq. or similar to OECD TG 310, 2003 - The ready biodegradability test was carried out according to ISO 14593 equivalent or similar to OECD TG 310 guideline. The test item, at a concentration of 25 mg/L was exposed in duplicate to activated sewage sludge micro-organisms obtained from the secondary treatment stage of the sewage treatment which treats predominantly domestic sewage (Villette: Geneva, Switzerland) with culture medium in sealed culture vessels in diffused light at 24°C ± 2°C for 28 days. The sludge was diluted in the test bottles to 20 mg DW/L. The degradation of the test item was assessed by the regular measurement of inorganic carbon (IC) production on days 0 and 28. This was achieved by measurement of the IC (Inorganic Carbon) in the headspace and the liquid phase of each vessel by gas-tight syringe and needle through the teflon septum (10 ml) and direct injection on the TOC (Total Organic Carbon) analyser. The sampling of the liquid phase was done through the bottom of the vessel and the sample was filtered on a 0.2 m filter prior to analysis. Analysis conducted in triplicate. The reference item attained 65% degradation after 5 days thereby confirming the suitability of the inoculum and test conditions. The mean biodegradation for duplicate test flasks at 28 days for the test item was 82.19%. It was considered the 10-day window was not met due to technical issue with the TOC analyser. However, the 10-d window does not apply to multi-constituent substances consisting of structurally similar constituents (OECD, 2006). Under the conditions of the study, test item is considered as readily biodegradable.