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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:
2013-08-21 to 2014-01-15
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
1997
Deviations:
no
Qualifier:
according to
Guideline:
other: ISO 10707 (1994) Water quality evaluation in an aqueous medium of the ultimate aerobic biodegradability of organic compounds. Method by analysis of biochemical oxygen demand (Closed Bottle test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands
- Method of cultivation: The activated sludge was preconditioned to reduce the endogenous respiration rates. To this end, 400 mg Dry Weight (DW)/L of activated sludge was aerated for one week.
- Concentration of sludge: 400 mg/kg DW/L
Duration of test (contact time):
28 d
Details on study design:
TEST CONDITIONS
- Composition of medium: The nutrient medium of the Closed Bottle test contained per liter 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.
- Additional substrate: Ammonium chloride was omitted from the medium to prevent nitrification.
- Test temperature: 22-24 °C
- pH: Start: 7.3, day 28: 7.2 (test and control), 7.3 (control with silica gel, mineral oil and methyl isobutyl ketone)
- pH adjusted: no
- Suspended solids concentration: solid stocks of 3.0, 0.38, and 1.1 mg substance/g silica gel
- The concentrations of the test substance, methyl isobutyl ketone, mineral oil and sodium acetate: 2.0, 0.25, 0.75 and 6.7 mg/L

TEST SYSTEM
- Culturing apparatus: 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.
- Number of culture flasks/concentration: 10 bottles containing only inoculum, 10 bottles containing silica gel and inoculum, 10 bottles containing inoculum and test substance, 10 bottles containing inoculum and methyl isobutyl ketone, 10 bottles containing inoculum and mineral oil, and 6 bottles containing sodium acetate and inoculum.
- Method used to create aerobic conditions: 400 mg Dry Weight (DW)/L of activated sludge was aerated for one week.
- Measuring equipment: The dissolved oxygen concentrations were determined electrochemically using an oxygen electrode (WTW TrioXmatic EO 200) and meter (WTW OXI 530) (Retsch, Ochten, The Netherlands). The pH was measured using a Eutech Cyberscan pH11 pH meter (Eutech Instruments, Nijkerk, The Netherlands). The temperature was measured and recorded with a sensor connected to a data logger.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Toxicity control: yes


STATISTICAL METHODS: Calculation of endogenous respiration, Calculation of the theoretical oxygen demand (ThOD), Calculation of the biochemical oxygen demand (BOD), Calculation of the biodegradation percentages
Reference substance:
acetic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
63
Sampling time:
28 d
Remarks on result:
other: test substance
Key result
Parameter:
% degradation (O2 consumption)
Value:
76
Sampling time:
28 d
Remarks on result:
other: active material
Details on results:
The biodegradability of test substance containing 44% of test substance(active) is biodegraded by 63% at day 28 in the Closed Bottle test. The biodegradability of both methyl isobutyl ketone and mineral oil was determined to enable calculation of biodegradation percentages for the active substance. Biodegradation percentages in excess of 60 at day 28 were also found with both methyl isobutyl ketone and mineral oil. The biodegradability of the active substance was calculated by first subtracting the oxygen consumption caused by methyl isobutyl ketone and mineral oil from the oxygen consumption due to degradation of the test substance. This gives an oxygen consumption of 1.3 mg/L for the active substance in the bottles at day 28. This oxygen consumption is divided by the ThOD of the active in the bottles i.e. 1.7 mg/L. This results in a biodegradation percentage of 76 at day 28 for the active substance. This biodegradation percentage is inaccurate due to the use of initial concentrations of mineral oil and methyl butyl ketone given in the SDS and especially the low percentage of active in the test substance. The result does, however, clearly, indicate that the active is readily biodegradable. The pass level of 60% was not reached within 14 days upon achieving 10% biodegradation. The test substance does therefore not meet the time window criterion. The test substance is a mixture of three chemicals. The biodegradation kinetics of the individual compounds in a mixture is not necessarily the same. The biodegradation of a mixture consisting of three organic compounds is an addition of different biodegradation curves. It is thus possible that the individual compounds meet the time window criterion whereas the biodegradability curve of the mixture suggests that the test substance is not readily biodegradable. The test item is therefore classified as readily biodegradable based on the biodegradation percentage of 63 (test substance) and 76 (active material) at day 28.
Results with reference substance:
Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of the test substance to microorganisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the inoculum by the test substance at day 7 was not detected. Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The biodegradability of the test substance was tested in a closed bottle test. The test substance was determined to be readily biodegradable.
Executive summary:

In order to assess the biotic degradation, a ready biodegradability test was performed which allows the biodegradability to be measured in an aerobic aqueous medium. The ready biodegradability was determined in the Closed Bottle test performed according to slightly modified OECD, EU and ISO Test Guidelines, and in compliance with the OECD principles of Good Laboratory Practice. The presence of the test substance with 44% active did not cause a reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum. The test substance and the active material were biodegraded by 63% and 76% at day 28, respectively. The test item is therefore classified as readily biodegradable. The pass level of 60 % was not reached within 14 days upon achieving 10 % biodegradation. The test substance does therefore not meet the time window criterion. The test substance is a mixture of three chemicals. The biodegradation kinetics of the individual compounds in a mixture is not necessarily the same. The biodegradation of a mixture consisting of three organic compounds is an addition of different biodegradation curves. It is thus possible that the individual compounds meet the time window criterion whereas the biodegradability curve of the mixture suggests that the test substance is not readily biodegradable. The test is valid as shown by an endogenous respiration of 0.7 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded by 78% of its theoretical oxygen demand after 14 days. Finally, the most important criterion was met by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Description of key information

The biodegradability of the test substance was tested in a closed bottle test. The test substance was determined to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

In order to assess the biotic degradation, a ready biodegradability test was performed which allows the biodegradability to be measured in an aerobic aqueous medium. The ready biodegradability was determined in the Closed Bottle test performed according to slightly modified OECD, EU and ISO Test Guidelines, and in compliance with the OECD principles of Good Laboratory Practice. The presence of the test substance with 44% active did not cause a reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum. The test substance and the active material were biodegraded by 63% and 76% at day 28, respectively. The test item is therefore classified as readily biodegradable. The pass level of 60 % was not reached within 14 days upon achieving 10 % biodegradation. The test substance does therefore not meet the time window criterion. The test substance is a mixture of three chemicals. The biodegradation kinetics of the individual compounds in a mixture is not necessarily the same. The biodegradation of a mixture consisting of three organic compounds is an addition of different biodegradation curves. It is thus possible that the individual compounds meet the time window criterion whereas the biodegradability curve of the mixture suggests that the test substance is not readily biodegradable. The test is valid as shown by an endogenous respiration of 0.7 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded by 78% of its theoretical oxygen demand after 14 days. Finally, the most important criterion was met by oxygen concentrations >0.5 mg/L in all bottles during the test period.