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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:
17 October 2016 - 16 November 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 1
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
1992
Qualifier:
according to
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Version / remarks:
1992
Qualifier:
according to
Guideline:
ISO 10707 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)
Version / remarks:
1994
GLP compliance:
yes (incl. certificate)
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Details on inoculum:
- River water was sampled from the Rhine near Heveadorp, The Netherlands (12 October 2016). 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. 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 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 not added to the river water to prevent nitrification (see also the section Any other information on materials and methods incl. tables)
Duration of test (contact time):
28 d
Initial conc.:
1 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
PREPARATION OF TEST SOLUTIONS
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 and the content was mixed vigorously. Subsequently 0.10 g of silica gel with the test substance was added to the test bottles. The resulting concentration of test substance in the bottles was 1.0 mg/L. Next the bottles were filled with nutrient medium with inoculum and closed.

TEST CONDITIONS
- Test temperature: 22-24°C
- pH: The pH of the media was 8.0 at the start of the test. The pH of the media at day 28 was 7.9 (test and control) and 8.0 (control with silica gel).
- pH adjusted at the start of the test: no
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.
- Number of culture flasks:
-- 10 bottles (only river water)
-- 10 bottles (river water and blank silica gel)
-- 10 bottles (river water and silica gel with test substance)
-- 6 bottles (river water and sodium acetate)
- Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles.

SAMPLING
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.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes (river water; river water with blank silica gel)
- Abiotic sterile control: no
- Toxicity control: no
Reference substance:
acetic acid, sodium salt
Remarks:
purity > 99%; concentration in test: 6.7 mg/L
Test performance:
The test is valid as shown by:
- an endogenous respiration of <1.5 mg/L (1.2 mg/L) after 28 days
- the differences of the replicate values at day 28 were less than 20%
- the reference sodium acetate was degraded by 83% of its theoretical oxygen demand after 14 days
- the oxygen concentrations were >0.5 mg/L in all bottles during the test period
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
7
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
10
Sampling time:
28 d
Details on results:
The substance is biodegraded by 10% at day 28 in the Closed Bottle test and should therefore be classified as not readily biodegradable.
Results with reference substance:
The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 83%

Toxicity to inoculum: was not seen in this test.

Validity criteria fulfilled:
yes
Remarks:
(see section Test performance)
Interpretation of results:
other: not readily biodegradable under the conditions of the test
Conclusions:
The substance is biodegraded by 10% at day 28 in the Closed Bottle test and should therefore be classified as not readily biodegradable.
Executive summary:

In order to assess the biodegradation of the substance, 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 1 mg/L of the substance for 28 days. The validity criteria of the test were met.

The substance was biodegraded by 10% at day 28 in the standard Closed Bottle screening test and should therefore be classified as not readily biodegradable under the conditions of the test (83% biodegradation of the sodium acetate reference substance after 14 days).

Description of key information

The ready biodegradability of the substance was investigated in a study conducted in river water following the procedures of OECD TG 301D (Closed Bottle Test) and GLP. The concentration tested was 1 mg/L substance. The validity criteria of the test were met. After 28 days, the substance was biodegraded for 10% and should therefore be classified as not readily biodegradable under the conditions of the test (83% biodegradation of the sodium acetate reference substance after 14 days).

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information