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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:
2017-03-08 to
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
yes
Remarks:
Test temperatures were between 20.0 and 22.7°C (mean: 21.2°C), thus not maintained in the range 22°C ± 1°C. This deviation was not considered to have not affected the outcome or the achievement of the study objectives.
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
The inoculum was obtained on 16 March April 2017 from the activated sludge of the biological wastewater treatment plant from Mourenx (France, 64) which handles predominantly domestic sewage.

On arrival at the laboratory, the sludge (around 800 mL) was centrifuged at approximately 20°C for 10 min at 1000 g; the solid sewage inoculant portion was re-suspended in dilution water in order to keep the concentration unchanged with respect to the sample. The inoculum was preconditioned 72 hours (aeration) until the flasks were inoculated.

Sub-samples of the homogenised sludge were dried in an oven at approximately 105°C and the suspended solids content was determined to be 5.36 g/L.

The inoculum was not adapted to the test item before the biodegradation test.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
A total of 9 bioreactors were used; 2 each for test item, blank control, reference item control, emulsifying agent control and one for toxicity control.

pH was measured in all flasks at the start and the end of the test period.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
49.3
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
53.1
Sampling time:
56 d
Details on results:
OXYGEN CONSUMPTION AND PERCENTAGE OF BIODEGRADATION
With regard to the oxygen consumption, the emulsifying agent could be considered as not toxic to bacteria and not biodegradable under the test conditions. As a consequence, oxygen consumption measured with blank controls was used for final calculations.

The maximum degradation level of the test item was 49.3% at day 28 (without nitrification) and 53.1% at day 56.

The test item did not inhibit the micro-organisms as shown by the toxicity control flask where biodegradation percentage is already 54.8%, higher than 25% after 14 days.

The reference item was readily biodegradable under the conditions of the test as >60% biodegradation was achieved by Day 14; this demonstrates the acceptable viability of the inoculum.

Theoretical Oxygen Demand

The theoretical oxygen demand of the test item is ThOD = 2.6123 mg O2/mg (based on CHN analysis). This calculation does not take into account any other constituents/impurities within the substance as supplied and is calculated by assuming formation of ammonium, water and carbon dioxide (no nitrification). If considering nitrification, ThODNO3 = 2.6854 mg O2/mg which is negligible.

Note: as no validated analytical method are is available, the results obtained are considered as non- GLP data.

The theoretical oxygen demand of sodium benzoate is 1.666 mg O2/mg.

Physical-Chemical Measurements

pH was measured in all flasks at the start and the end of the test period, values are comprised between 7.4 and 7.9. 

Recorded test temperatures where between 20.0 and 22.7°C (mean: 21.2°C).

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
According to the OECD 301 guideline, the pass level for ready biodegradability is 60% of ThOD for respirometric methods. This pass value has to be reached in a 10-d window within the 28-d period of the test; the 10-d window begins when the degree of biodegradation has reached 10% ThOD and must end before day 28 of the test.

In this study, the biodegradation did not reach the pass level 60% of ThOD at Day 28. As a consequence, the test item Reaction mass of decyl acrylate and octyl acrylate was not readily biodegradable under the conditions of the test.
Executive summary:

The study was conducted in accordance with procedures outlined in OECD Guideline 301F. The ready biodegradability of Reaction mass of decyl acrylate and octyl acrylate was assessed over a 56 days period (in absence of the CHN analysis at Day 28, the test was extended until Day 56 as the test item biodegradation was close to the pass level (60%) at Day 28).

The test was conducted at a nominal loading rate of 100 mg/L. As test item is known to be difficult to dissolve, its dispersibility was improved by use of an emulsifying agent (Symperonic P103) as described in ISO 10634 standard.

A total of 9 bioreactors were used; 2 each for test item, blank control, reference item control, emulsifying agent control and one for toxicity control.

The results of the test were as follows:

% biodegradation

Test item

(mean of replicates)

Reference item

(mean of replicates)

Toxicity Control

28 days

49.3%

96.2%

63.4%

56 days

53.9%

95.6%

66.6%

The test item was not readily biodegradable under the conditions of the test as it failed to achieve a transition from 10% to 60% degradation in a 10-day window during the 28 days test.

 

The test item was not considered to be inhibitory to the microbial inoculum since the biodegradation observed in the toxicity control bioreactor was not less than 25% occurred within 14 days.

The definitive test met the validity criteria of the test guideline detailed as follows:

  • the difference of extremes of replicate values of the removal of the test item at the end of the test was less than 20%
  • the percentage degradation of the reference compound reached the pass levels by day 14: 93.0%
  • the biodegradation observed in the toxicity control bioreactor was not less than 25% occurred within 14 days: 54.8%
  • the oxygen uptake of the inoculum blank (emulsifying agent control) was not greater than 60 mg/L in 28 days: 29.3 mg/L (and 42.6 mg/L at Day 56)
  • the pH value was not outside the range 6-8.5: min 7.4, max 7.9

Description of key information

A biodegradation in water screening test was conducted in accordance with procedures outlined in OECD Guideline 301F. The ready biodegradability of Reaction mass of decyl acrylate and octyl acrylate was assessed over a 56 days period.

The test item biodegradation reached 49.3% (ThOD) 28 days after the beginning of the trial and 53.1% at day 56. According to the OECD 301 guideline, the pass level for ready biodegradability is 60% of ThOD for respirometric methods. Consequently, the test item Reaction mass of decyl acrylate and octyl acrylate was not readily biodegradable under the conditions of the test.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information