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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:
from 29 July until 26 August 2005
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
see the section "overall remarks" for discussion of the restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
Ammonium chloride was omitted from the medium to prevent nitrification. The biodegradation of the reference compound was 58% instead of > 60%. These deviations did not influence the integrity of the study (see details on results).
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
About 0.5 litre secondary (biological) activated sludge was obtained from the RWZI Horstermeer in Nederhorst den Berg, The Netherlands on 22 July 2005. The RWZI Horstermeer is an activated sludge plant treating predominantly domestic waste water. The sludge was preconditioned to reduce the endogenous respiration rate. This was done by aerating the sludge (50 mg dry weight per litre mineral salt solution) at 20 +/- 1°C for one week. After this the sludge was diluted to a concentration in the test bottles of 2 mg dry weight per litre.
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Preparation of stock solutions :
A sodium acetate stock solution of 1 g/L was prepared by dissolving 200.2 mg sodium acetate in 200 mL closed bottle medium.
For F1EC a stock solution of 200 mg/L was prepared by dissolving 100 mg F1EC in 500 mL closed bottle medium.

Preparation of test solutions :
Ten bottles of group A (number 1-10) were completely filled with closed bottle medium. The other bottles were filled with about 100 mL closed bottle medium and thereafter the bottles were filled as follows :
Group B (number 11-20): 11.2 mL inoculum
Group C (number 21-30): 1.85 mL sodium acetate stock solution and 11.2 mL inoculum
Group D (number 31-40) : 1.85 mL sodium acetate stock solution, 14 mL F1EC stock solution and 11.2 mL inoculum
Group E (number 41-50): 14 mL F1EC stock solution and 11.2 mL inoculum
Hereafter the bottles were completely filled with closed bottle medium (to avoid a headspace) to an endvolume of 280 mL and closed with glass stoppers sealed with silicon paste. F1EC and sodium acetate concentrations were 10 and 6.6 mg/L, respectively.
After filling, the bottles were incubated in a thermostated room in the dark at 20 +/- 1°C. The temperature was recorded once every hour with the YOKOGAWA temperature registration system.

Oxygen and pH measurements
Immediatly after filling the bottles (day 0) and after 7, 14, 21 and 28 days the oxygen content was measured in two bottles of group A, B,C, D and E. The pH was measured on day 0 and day 28 in two bottles of each group.

Calculation of the biodegradation
The biodegradation was calculated as the ratio of the biochemical oxygen demand (BOD) and the theoritical oxygen demand (ThOD). The BOD is the amount of oxygen consumed by micro-organisms to metabolise a test compound. The ThOD is the total amount of oxygen required to oxidise a chemical completely and is calculated from the molecular formula.
The ThOD of F1EC is 0.6 g O2 per gram test substance. The ThOD of sodium acetate is 0.78 g O2 per gram test substance. The BOD of the test substance and sodium acetate was calculated from the oxygen contents in the test bottles with and without test substance (group E and B) and the bottles with and without sodium acetate (group C and B), respectively. The bottles of group D were used as a toxicity control. If F1EC is toxic to micro-organisms the biodegradation of sodium acetate is inhibited in these bottles.
Reference substance:
acetic acid, sodium salt
Test performance:
The temperature was recorded once every hour with the YOKOGAWA temperature registration system and ranged between 19.6 and 20.5 °C.

Validation of the test conditions :
- The measured oxygen content at the start of the experiment was 8.4 - 8.5 mg/L and therefore met the validity crietrion of 8 - 10 mg/l at test initiation.
- The oxygen depletion in the inoculum blank was at maximum 0.70 mg/L O2 (on day 21), which is in agreement with an oxygen consumption of < 1.5 mg/L after 28 days.
- The biodegradation of sodium acetate in the control series (group C) was 51, 49, 38 and 58% on day 7, 14, 21 and 28, respectively. According to the OECD guideline 301 the percentage biodegradation of the reference compound must be higher than 60% on day 28. As 58% does not significantly differ from 60% and the test compound itself was degraded for > 60% within 14 days it can still be concluded that the microbial activity of the inoculum was sufficient.

Deviations from protocol :
- In SOP HES 600 009 it is stated that the test solutions should be stirred during measurement of oxygen concentration. In practice it is not possible to stir the test solution without introducing oxygen. Therefore the test solutions were not stirred during measurement of oxygen concentration.
- The biodegradation of sodium acetate in the control series (group C) was 51, 49, 38 and 58% on day 7, 14, 21 and 28, respectively. According to the OECD guideline 301 the percentage biodegradation of the reference compound must be higher than 60% on day 28. As 58% does not significantly differ from 60% and the test compound itself was degraded for > 60% within 14 days it can still be concluded that the microbial activity of the inoculum was sufficient.
- To the opinion of the study director these deviations did not influence the integrity of the study.
Key result
Parameter:
% degradation (O2 consumption)
Value:
47
Sampling time:
7 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
68
Sampling time:
14 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
38
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
65
Sampling time:
28 d
Details on results:
F1EC was not toxic to the micro-organisms, because sodium acetate was degraded in the presence of F1EC for more than 25%.
F1EC was significantly degraded (68% within 14 days at 20°C) and according to the OECD guidelines F1EC can therefore be classified as readily biodegradable.
Results with reference substance:
Points of degradation plot (reference substance):
51 % degradation after 7 d
49 % degradation after 14 d
38 % degradation after 21 d
58 % degradation after 28 d

 Table 1 : Measured values of the oxygen content (mg/L) in the test bottles

 Sampling time

(days)

 A

medium

 B

medium + inoculum

 C

medium + inoculum + sodium acetate

 D

medium + inoculum + sodium acetate + F1EC

 E

medium + inoculum + F1EC

 0  8.5  8.5  8.4  8.4  8.4
 0  8.5  8.5  8.4  8.4  8.4
 7  8.3  8.0 5.8  4.5  5.7
 7  8.4  8.2  5.2  4.3  4.9
 14  8.1  8.0  5.4  1.4  4.1
 14  8.6  8.2  5.8  1.4  4.0
 21(A)  8.6  7.8  6.4  3.9  6.2
 21(A)  8.5  7.9  5.4  3.0  5.0
 28  8.9  7.9  5.0  2.5  3.8
 28  8.4  8.2  5.1  3.5  4.5

(A) The measured oxygen concentrations after 21 days are lower than expected. A possible explanation is that there was no equilibrium yet during the measurement which means that the actual oxygen concentrations were lower. After 28 days the measured oxygen concentrations are in line again with the expected values.

  Table 2 : Measured values of the pH in the test bottles
 Sampling time (days)

 A

medium

 B

medium + inoculum

 C

medium + inoculum + sodium acetate

 D

medium + inoculum + sodium acetate + F1EC

 E

medium + inoculum + F1EC

 0  7.3  7.3  7.3  7.3  7.2
 0  7.3  7.3  7.3  7.2  7.2
 28  7.4  7.3  7.2  7.0  6.8
 28  7.3  7.2  7.2  6.9  6.7
Validity criteria fulfilled:
no
Remarks:
see discussion in the section "overall remarks"
Interpretation of results:
readily biodegradable
Conclusions:
Under the condition of this study, F1EC was found to be around 68% degraded in 14 days.
Executive summary:

The biodegradability of F1EC (MONOFLUOROETHYLENE CARBONATE) was determined following OECD TG 301D (1992) and according to the OECD GLP principles.

F1EC was added to an aqueous mineral salt medium and exposed to relatively low numbers of unadapted microorganisms under aerobic conditions for a period of 28 days. The test compound was the only source of carbon and energy which was available to micro-organisms. To follow the biodegradation of F1EC, the oxygen consumption by the micro-organisms was determined.

The reference compound sodium acetate was degraded for 49% and 58% within 14 and 28 days respectively. According to OECD TG 301 the percentage of biodegradation of the reference compound must be higher than 60% by day 14. As the test compound itself was degraded for > 60% within 14 days it can still be concluded that the microbial activity of the inuculum was sufficient.

Sodium acetate was also degraded in the presence of F1EC during the test period. This indicates that F1EC is not toxic to the micro-organisms at the tested concentration of 10 mg/L.

F1EC was significantly degraded (i.e. 68% within 14 days) and according to the guideline F1EC can therefore be classified as readily biodegradable.

Description of key information

FEC was significantly degraded (i.e. 68% within 14 days) and according to the guideline FEC can therefore be classified as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information