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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:
08 November 2016 to 06 December 2016
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:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Aeration tank of Sewage Treatment Plant ”Czajka”, Warsaw
- Storage conditions: 22 ºC, aerated.
- Storage length: 5 days.
- Preparation of inoculum for exposure: The coarse particles were removed by settling and the supernatant was discarded. The sludge was washed in the mineral medium. The concentrated sludge was suspended in mineral medium to yield a concentration of 3-5 g suspended solids/l and it was aerated for 5 days, at the test temperature of 22 °C, up to application. A sample was withdrawn just before use for the determination of the dry weight of the suspended solids.
- Concentration of sludge: 30 mg suspendend solids/L in mineral medium.
- Water filtered: no
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
ThOD
Remarks:
50-100 mg ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium:
concentration of elements in mineral medium (mg/L)
P 116 mg/L
N 1,3 mg/L
Na 86 mg/L
K 122 mg/L
Mg 2.2 mg/L
Ca 9.9 mg/L
Fe 0.05–0.1 mg/L
pH 7.4 ± 0.2

- Additional substrate: The double-distilled water was taken from redistillation set. It must contain no more than 10% of the organic carbon content introduced by the test material. There is 100 mg/L of test item what gives 56.4 mg/L of organic carbon. Thus, the used water must contain less than 5.64 mg/L of organic carbon. This was checked by DOC analysis. The measured value was about 4 mg/L of organic carbon
- Test temperature: 22 ± 0.4 ºC
- pH: 7.4
- pH adjusted: no
- Aeration of dilution water: not specified.
- Suspended solids (SS) concentration: 30 mg SS/L in mineral medium.
- Continuous darkness: no

TEST SYSTEM
- Culturing apparatus: Respirometer flask.
- Number of culture flasks/concentration: Three flask containing the test item, inoculum blank or reference substance. Two flasks for toxicity check and one abiotic sterile control.
- Method used to create aerobic conditions:At first, the open sample bottles were filled with the suitable mineral solutions, test substances, inoculum under aerobic conditions. Then, the measuring heads were screwed onto the sample bottels and closed tightly.
- Measuring equipment: Oxitop OC110 respirometer, spectrophotometer Hach DR3900 and 45600 reactor for TOC measurements, electronic temperature recorder EBI-310 T, pH meter Elmetron CX-505
- Details of trap for CO2 and volatile organics if used: The CO2 evolved during test item degradation was absorbed in a solution of potassium hydroxide.

SAMPLING
The oxygen uptake was measured every 112 min during the 28 day test.
The oxygen uptake was measured in a specific equipment, i.e. OxiTop OC 110 respirometers flasks which are prepared to automatically measure the oxygen uptake.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes, containing only inoculum 30mg/L SS.
- Abiotic sterile control: Yes, containing test item, at the same concentrations as in the individual solutions 30 mg/L SS and sterilizing agent at a concentration of 0.1 % ( Mercury (II) chloride).
- Toxicity control: Yes, containing test item, reference item at the same concentrations as in the individual solutions and inoculum 30 mg/L SS.

STATISTICAL METHODS:
The calculations and the graphs were performed using SigmaP lot 9.0 software of SYSTAT Software, Inc., USA purchased from GAMBIT CoiS Ltd, Poland.
Reference substance:
acetic acid, sodium salt
Remarks:
Sodium acetate, anhydrous
Key result
Parameter:
% degradation (O2 consumption)
Remarks:
Based on COD
Value:
75.3
Sampling time:
28 d
Key result
Parameter:
COD
Value:
2.28 g O2/g test mat.
Parameter:
ThOD
Value:
2.15 g O2/g test mat.
Remarks on result:
other: This value was estimated based on gross asumptions on the composition of the subtance. It is considered a reliability check for the % biodegradation based on COD.
Results with reference substance:
The reference substance reached 96.1 % biodegradation and the level for ready biodegradability by 6 days.

The test item is a complex UVCB substance consisting of several constituents with different chain-lenght. A test on the complex substance was performed. A sequential biodegradation of the individual constituents was expected, therefore, according to the Guidance on the application of CLP Criteria (Version 4.1., page 563), the ten -day window was not applied to interprete the results. The biodegradability was assessed after the 28 day test period.

Validity criteria fulfilled:
yes
Remarks:
The difference of the BOD at the plateau and at the end of the test was < 20%.The reference reached the pass level on day 6.The oxygen uptake of the blank is 36.9 mg O2/l in 28 days. The pHs were inside the range 6-8.5.
Interpretation of results:
readily biodegradable
Conclusions:
The test item attained 75.3 % biodegradation in 28 days in the manometric respirometry test.
Executive summary:

A screening test was conducted to determine the ready biodegradability of the test item according to OECD method 301F, Manometric respirometry test. The study was conducted under GLP conditions. Inoculum blanks, procedure control with reference susbtance, toxicity control and abiotic sterile control were concurrently conducted. The % biodegradation was calculated based on COD because of the UVCB nature of the test item, however, the reliability of the experimental value was verified by a estimated ThOD. The validity criteria was fulfilled. The test item attained 75.3 % biodegradation in 28 days in the manometric respirometry test.

Description of key information

Key study: Test method according to OECD 301F, Manometric respirometry test. GLP study. The test item achieved 75.3 % biodegradation in 28 days,therefore, it is regarded as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The test item is a complex UVCB substance consisting of several constituents with different chain-lenght. A test on the complex substance was performed. A sequential biodegradation of the individual constituents was expected, therefore, according to the Guidance on the application of CLP Criteria (Version 4.1., page 563), the ten -day window was not applied to interpret the results. The biodegradability was assessed after the 28 day test period.