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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:
2018-11-05 - 2018-12-06
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
minor deviation from the guideline: ammonium chloride was omitted from the medium to prevent oxygen consumption due to nitrification (omission does not result in nitrogen limitation as shown by biodegradation of the reference compound)
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
ammonium chloride was omitted from the medium to prevent oxygen consumption due to nitrification (omission does not result in nitrogen limitation as shown by the biodegradation of the reference compound).
Principles of method if other than guideline:
Minor deviations from the guidelines of the Closed Bottle test (OECD TG 301D) were introduced; a) ammonium chloride was omitted from the medium to prevent oxygen consumption due to nitrification (omission does not result in nitrogen limitation as shown by the biodegradation of the reference compound), and b) river water instead of an effluent/extract/mixture was used as inoculum.
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on inoculum:
River water was sampled from the Rhine near Heveadorp, The Netherlands (01-11-2018). The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream. The river water was aerated for 7 days before use to reduce the endogenous respiration (van Ginkel and Stroo, 1992). River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating.
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 bottles
The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.

Nutrients, stocks and administration
The river water used in the Closed Bottle test was spiked per liter of water with 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.4 mg Na2HPO4·2H2O, 22.5 mg MgSO4·7H2O, 27.5 mg Ca¬Cl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was not added to the river water to prevent nitrifi-cation. The test substance was added to the bottles using aqueous stock emulsion of 1.0 g/L. Sodium acetate was added to the bottles using aqueous stock solution of 1.0 g/L.n of 1.0 g/L.

Test procedures
The Closed Bottle test (OECD TG 301D) was performed according to the study plan. The study plan was develo¬ped from ISO Test Guidelines (1994). Use was made of 10 bottles con-taining only river water, 6 bottles con¬taining river water and sodium acetate, 10 bottles con-taining river water with test substance. The con¬centrations of the test substance, and sodium ace¬tate in the bottles were 2.0 and 6.7 mg/L, res¬pectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were com¬pletely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bot¬tles were closed and incubated in the dark. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.

Calculation of endogenous respiration
The endogenous respiration (oxygen depletion in the control) was calculated as follows;
Oxygen depletion (endogenous respiration) (mg/L) = Mc (day 0) - Mc (day 28)
Mc is the mean oxygen level in the control bottle with river water.

Calculation of the theoretical oxygen demand (ThOD)
The ThODs of the test item and sodium acetate were calculated from their molecular formulae and molecular weights

Calculation of the biochemical oxygen demand (BOD)
Provided that the oxygen concentrations in all bottles at the start of the test were equal, the amounts of oxygen consumed in test and reference compound bottles were calculated as follows:
Oxygen consumptionn (mg/L) by test substance = Mc - Mt
Oxygen consumptionn (mg/L) by reference compound = Mc - Ma
Mc is the mean oxygen level in the control bottles n-days after the start of the test.
Mt or a is the mean oxygen concentration in the bottles containing the test substance (t) or the reference compound, sodium acetate (a), n-days after the start of the test.
The biological oxygen demand (BOD) mg/mg of the test substance and sodium acetate was cal¬culated by dividing the oxygen consumption by the concentration of the test substance and so¬dium acetate in the closed bottle, respectively.

Calculation of the biodegradation percentages
The biodegradation was calculated as the ratio of the biochemi¬cal oxygen demand (BOD) to the theoretical oxygen demand (ThOD).
Reference substance:
acetic acid, sodium salt
Remarks:
Supplier: Sigma-Aldrich, St Louis, US; Purity >99% ; Batch/lot number BCBP8197V
Key result
Parameter:
% degradation (O2 consumption)
Value:
66
Sampling time:
28 d
Remarks on result:
other: readily biodegradable
Details on results:
The calculated theoretical oxygen demand (ThOD) of the main constituent of the test item is 2.64 g oxygen/g test substance. The ThOD was calculated with the molecular formula of the test item derived from its structure. The ThOD of sodium acetate is 0.78 g oxygen/g sodium acetate

Toxicity
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 substances to micro¬organisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the ino¬culum by the test substance at day 7 was not detected (Table I). Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.

Biodegradability
Tetradecyl ethoxylated glycidylether was biodegraded by 66% at day 28 in the Closed Bottle test (Table II, Figure). The time-day window concept assumes that biodegradation of a single organic compound in a ready biodegradability test is a growth-linked process which follows an S-shaped growth curve. Tetradecyl ethoxylated glycidylether (UVCB) is a mixture of chemicals. The biodegradation kinetics (lag period, growth rate, and yield) of the individual chemicals in a mixture are not necessarily the same. The biodegradation of a substance consisting of many constituents is therefore an addition of different biodegradation curves. It is thus possible that individual compounds meet the time window criterion whereas the biodegradability curve of the multi-constituent suggests that the test substance is not readily biodegradable. The time window applied as criterion to Closed Bottle tests is therefore considered not applicable to multi-constituents and UVCBs (OECD, 2006). The test item is therefore classified as readily biodegradable only based on the >60% reached at day 28.


Results with reference substance:
The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 92..

Oxygen consumption (mg/L) and the percentage biodegradation of the test substance (BOD/ThOD) and sodium acetate (BOD/ThOD) in the Closed Bottle test

Time (days)

Oxygen consumption (mg/L)

Biodegradation (%)

 

Test substance

Acetate

Test substance

Acetate

0

0.0

0.0

0

0

7

2.3

4.8

44

92

14

2.6

4.8

49

92

21

3.5

 

66

 

28

3.5

 

66

 

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item should be classified as readily biodegradable.
Executive summary:

In order to assess the biotic degradation of tetradecyl ethoxylated glycidylether, 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 test item did not cause a reduction in the endogenous respiration at day 7. The test substance is therefore con­sidered to be non-inhibitory to the inoculum. The test item was biodegraded by 66% at day 28 in the OECD 301D Closed Bottle test and should therefore be classified as readily biodegradable.

The test is valid as shown by an endogenous respiration of 1.1 mg/L and by the total mineraliza­tion of the reference compound, sodium acetate. Sodium acetate was degraded by 92% 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

In order to assess the biotic degradation of tetradecyl ethoxylated glycidylether, 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 test item did not cause a reduction in the endogenous respiration at day 7. The test substance is therefore con­sidered to be non-inhibitory to the inoculum. The test item was biodegraded by 66% at day 28 in the OECD 301D Closed Bottle test and should therefore be classified as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information