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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:
19-09-2018 to 23-10-2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study performed under GLP. All relevant validity criteria were met.
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
inspected: August 2017 ; signature: September 2017
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): 1. Secondary activated sludge was obtained from the wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands. This plant is an activated sludge plant treating predominantly domestic wastewater.
- Storage conditions: See pretreatment field.
- Storage length: < 1 week
- Preparation of inoculum for exposure: See pre-treatment field.
- Pretreatment: The activated sludge was preconditioned to reduce the endogenous respiration rates. To this end, 0.4 g Dry Weight (DW)/L of activated sludge was aerated for one week. The sludge was diluted in the bottles to 2.0 mg/L.
- Concentration of sludge: The sludge was diluted in the BOD bottles to 2 mg DW/L
Duration of test (contact time):
28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: The nutrient medium of the Closed Bottle test contained per litre of deionized water; 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.3 mg Na2HPO4.2H2O, 22.5 mg MgSO4.7H2O, 27.5 mg CaCl2, 0.25 mg FeCl3.6H2O. Ammonium chloride was omitted from the medium to prevent nitrification.
- Solubilising agent (type and concentration if used): None.
- Test temperature: Temperatures were within the prescribed temperature range of 22 to 24°C (Actual: 22.6 to 22.9°C).
- pH: The pH of the media (activated sludge) was 7.3 at the start of the test. The pH of the medium at day 28 was 7.3 (controls) and 7.2 (test)
- pH adjusted: No.
- Aeration of dilution water: Not reported
- Suspended solids concentration: 2 mg/L dry weight
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.
- Number of culture flasks/concentration: 2 bottles containing only inoculum per time point (10 bottles total) ; 2 bottles containing test item with inoculum per time point (10 bottles total) ; 2 bottles containing test item and reference item and inoculum per time point (10 bottles total)
- Measuring equipment: See details on analytical methods. The dissolved oxygen concentrations were determined electrochemically using an oxygen electrode and meter. The pH was measured using a pH meter. The temperature was measured and recorded with a sensor connected to a data logger.
- Test performed in closed vessels due to significant volatility of test substance: No.
- Test performed in open system: No.

SAMPLING
- Sampling frequency: Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.
- Sampling method: Analyses of the dissolved oxygen concentration
- Sterility check if applicable: No.
- Sample storage before analysis: Not applicable.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes.
- Abiotic sterile control: No.
- Toxicity control: Yes (where applicable)
- Other: Positive reference control (Sodium Acetate)
Reference substance:
acetic acid, sodium salt
Remarks:
6.7 mg/L
Test performance:
1. The endogenous respiration was 1.1 mg/L at day 28 (i.e. < 30 mgO2/L after 28 days)
2. The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled for the flasks containing test item at end of 14-day window and on day 28.
3. The pH at day 28 was in the range of 6.0 to 8.5 (actual 7.2 to 7.3 for controls and test item vessels)
4. Sodium Acetate attained 81% degradation at 14 days thereby confirming the suitability of the inoculum and test conditions.
5. Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test item in the Closed Bottle test was not determined because possible toxicity of the test item to microorganisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the inoculum by the test item at day 7 was not detected.
Parameter:
% degradation (O2 consumption)
Value:
64
Sampling time:
28 d
Remarks on result:
other: 14-day window met
Details on results:
The 10-day window criteria was not met in all replicates.
Results with reference substance:
Sodium Acetate attained 81% degradation after 14 days thereby confirming the suitability of the inoculum and test conditions.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The mean biodegradation in triplicate was 64 % at day 28. The 14-day window criteria was met.
Executive summary:

The ready biodegradability test was carried out according to OECD TG 301D guideline under GLP. The test item at a concentration of 2 mg/L was exposed to activated sewage sludge micro-organisms obtained from the secondary treatment stage of the sewage treatment which treats predominantly domestic sewage in sealed BOD vessels and in the dark at 22°C ± 1°C for 28 days. The inoculum concentration was 2 mg/L DW in the BOD bottles. Degradation was assessed by the measurement of oxygen consumption via dissolved oxygen concentration measurement. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28. Control solutions with inoculum and the reference substance: sodium acetate, together with a toxicity control (where applicable) were used for validation purposes. The endogenous respiration was 1.1 mg/L at day 28. The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled for the flasks containing test item at end of 14-day window and on day 28. The pH at day 28 was in the range of 6.0 to 8.5 (actual 7.2 to 7.3 for controls and test item vessels). Sodium Acetate attained 81% degradation at 14 days thereby confirming the suitability of the inoculum and test conditions. The mean biodegradation for the test item at 28 days was 64% and the 14-day window was met. Under the conditions of the study, test item is considered to be readily biodegradable.

Description of key information

Biodegradation: readily biodegradable, mean biodegradation 64 % (28 -days; 14-day window met), OECD TG 301D, 2018

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

Key Study: OECD TG 301D, 2018 : The ready biodegradability test was carried out according to OECD TG 301D guideline under GLP. The test item at a concentration of 2 mg/L was exposed to activated sewage sludge micro-organisms obtained from the secondary treatment stage of the sewage treatment which treats predominantly domestic sewage in sealed BOD vessels and in the dark at 22°C ± 1°C for 28 days. The inoculum concentration was 2 mg/L DW in the BOD bottles. Degradation was assessed by the measurement of oxygen consumption via dissolved oxygen concentration measurement. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28. Control solutions with inoculum and the reference substance: sodium acetate, together with a toxicity control (where applicable) were used for validation purposes. The endogenous respiration was 1.1 mg/L at day 28. The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled for the flasks containing test item at end of 14-day window and on day 28. The pH at day 28 was in the range of 6.0 to 8.5 (actual 7.2 to 7.3 for controls and test item vessels). Sodium Acetate attained 81% degradation at 14 days thereby confirming the suitability of the inoculum and test conditions. The mean biodegradation for the test item at 28 days was 64% and the 14-day window was met. Under the conditions of the study, test item is considered to be readily biodegradable.