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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:
06 September 2017 - 05 October 2017
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)
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Details on inoculum:
River water was sampled from the Rhine near Heveadorp, The Netherlands. The river water was aerated for 7 days to reduce the endogenous respiration. River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating. The river water was spiked with mineral salts. Ammonium chloride wasa not added to the river water to prevent nitrification.
Duration of test (contact time):
28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
as a percentage of ThOD
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 CaCl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was omitted from the medium to prevent nitrification. Accurate administering of the test substance was accomplished by preparing a solid stock of 3.0 mg of the test substance per g of silica gel in a 50-mL serum flask. Only part of the top layer of the silica gel was brought into contact with the test substance. The serum flask was closed with a screw top with aluminium foil and the content was mixed vigorously. Subsequently 0.2 g of silica gel with the test substance was added to the test bottles. The resulting concentration of test substance in the bottles was 2.0 mg/L. Next the bottles were filled with nutrient medium with inoculum and closed. Sodium acetate was added to the bottles using a stock solution of 1.0 g/L.

Test procedure:
Use was made of 10 bottles containing only river water, 10 bottles containing river water and silica gel, 10 bottles containing river water and silica gel with test substance, 6 bottles with river water and sodium acetate. The concentrations of the test substance, and sodium acetate in the bottles were 2.0 and 6.7 mg/L, respectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles 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.

Test conditions:
The pH of the media was 8.0 at the start of the test. The pH of the medium at day 28 was 8.0 (controls) and 7.9 (test). The temperature ranged from 22.9 to 23.5°C which is within the prescribed temperature range of 22 to 24°C.
Reference substance:
acetic acid, sodium salt
Remarks:
purity > 99%
Test performance:
The test is valid as shown by an endogenous respiration of 1.2 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%. Sodium acetate was degraded by 85% 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.
Key result
Parameter:
% degradation (O2 consumption)
Value:
67
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
66
Sampling time:
21 d
Parameter:
% degradation (O2 consumption)
Value:
60
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
29
Sampling time:
7 d
Details on results:
Geranium oil (UVCB) was biodegraded by 67% at day 28 in the Closed Bottle test. Over 60% biodegradation was achieved in a period of approximately 12 days immediately following the attainment of 10% biodegradation after 2 days. The test item therefore fulfilled the 14-day time window (10-day time window for other OECD 301 tests) criterion for ready biodegradable compounds. Geranium oil (UVCB) should as a consequence be classified as readily biodegradable.
Results with reference substance:
The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 85.

Toxicity to inoculum:

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 Geranium oil (UVCB) 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
Remarks:
The reference substance, toxicity of the test substance, the difference of the replicates at 28d, O2 depletion (inoculum blank) and residual O2 conc in the test bottles met the validity criteria.
Interpretation of results:
readily biodegradable
Conclusions:
The substance is biodegraded by 67% at day 28 in the Closed Bottle test and should therefore be classified as readily biodegradable.
Executive summary:

In order to assess the biodegradation of Geranium oil, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study river water was exposed to 2 mg/L of the substance for 28 days. The test substance did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met. Geranium oil was biodegraded by 67% at day 28 in the standard Closed Bottle screening test and should therefore be classified as readily biodegradable.

Description of key information

In order to assess the biodegradation of Geranium oil, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study river water was exposed to 2 mg/L of the substance for 28 days. The test substance

did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met. Geranium oil was biodegraded by 67% at day 28 in the standard Closed Bottle screening 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