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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:
06.02. – 10.03. 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): The inoculum contained a mixed population of microorganisms obtained from the secondary effluent of the waste water treatment plant of Pardubice processing predominantly municipal sewage. - Preparation of inoculum for exposure: The fresh collected waste water was filtered through paper filter. COD was determined and waste water was aerated till using.The inoculum preparation is in conformity with the recommendations of the test guideline.
Duration of test (contact time):
28 d
Initial conc.:
2.5 mg/L
Based on:
test mat.
Remarks:
(COD 1.90 mg·L-1)
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The volume of waste water for the inoculation of mineral medium was chosen 2.2 mL per 1 L of medium (COD of waste water: 47 mg·L-1). 30 L aerated mineral medium was prepared for the test and before the beginning of the test it was inoculated with 66 mL of modified waste water. The pH value of medium: 7.5.TEST CONDITIONSThe stock solution of the test substance was prepared in concentration 0.1012 g·L-1 of deionized water. From this solution 148.2 mL (24.7 mL·L-1) were transferred to a large glass bottle and completed with the inoculated medium to the volume of 6 L. - Composition of medium:Preparation of 1 litre of mineral medium: 1 mL of solutions a), b), c) and d) were mixed with approx. 500 mL of water, the mixture was replenished with water up to 1 000 mL. The solution was prepared from aerated water. Solution a) Monopotassium dihydrogen orthophosphate, (KH2PO4) 8.50 gDipotassium monohydrogen orthophosphate, (K2HPO4) 21.75 gDisodium monohydrogen orthophosphate dihydrate, (Na2HPO4·2H2O) 33.40 gAmmonium chloride (NH4Cl) 0.50 g Water up to the volume of 1 000 mLSolution b) 22.50 g Magnesium sulphate heptahydrate, (MgSO4·7H2O) in 1 000 mL of waterSolution c) 27.50 g Calcium chloride, anhydrous, (CaCl2) in 1 000 mL of waterSolution d) 0.25 g Iron (III) chloride hexahydrate, (FeCl3·6H2O) in 1 000 mL of water - Solubilising agent (type and concentration if used): The deionized water with conductivity less than 5 uS·cm-1 was used for the preparation of all solutions. - Test temperature: 20±1.0 °C - pH: 7.4 - pH adjusted: The right composition of medium was checked by the determination of pH value, which must be 7.4. - Aeration of dilution water: yes - Continuous darkness: yes TEST SYSTEMTest substance series:2 x 9 bottles with test substance and inoculumReference substance series:2 x 9 bottles with reference substance and inoculumBlank series:2 x 9 bottles with inoculated medium onlyToxicity test series:2 x 5 bottles with test substance, reference substance and inoculum for toxicity testSeries for nitrification determination:1 x 9 bottles with test substance and inoculumThe prepared dosing solutions for each series were filled in two parallel bottle replicates (except series for nitrification determination).The bottles were placed into thermostat.- Method used to create aerobic conditions: the solution was prepared from aerated water - Measuring equipment: oximeter WTW OXI 730 - Test performed in open system: no SAMPLING - Sampling frequency: at the zero-time and at the 3rd, 7th, 10th, 14th, 17th, 21st, 24th and 28th day of the test - Sampling method: the appropriate bottles from each series were taken off CONTROL AND BLANK SYSTEM - Inoculum blank: yes, the inoculated mineral medium - Toxicity control: yes, with the mixture contained 2.50 mg·L-1 of the test substance and 2.10 mg·L-1 of sodium benzoate (mixture COD 5.35 mg·L-1).
Reference substance:
benzoic acid, sodium salt
Test performance:
Degradation is determined by analysis of dissolved oxygen over a 28-day period. The following determinations were done simultaneously under the same conditions:- check of inoculum activity with the reference substance- toxicity test of the test substance for used inoculum in mixture of the test and reference substance- determination of oxygen consumption for nitrification- determination of blank (inoculated mineral medium)The amount of oxygen taken up by the test chemical, corrected for uptake by the blank inoculum run in parallel, is expressed as a percentage of COD.
Key result
Parameter:
% degradation (O2 consumption)
Value:
22.8
Sampling time:
28 d
Key result
Parameter:
COD
Value:
0.761 other: mg·mg-1
Parameter:
BOD5
Value:
0.119 other: mg·mg-1
Results with reference substance:
Sodium benzoate COD 1.643 mg·mg-1
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
In this 28-day study of ready biological degradability the degradation of 22.8 % of the test substance, Direct Blue 85, was attained in the end of study.
Executive summary:

The test substance, Direct Blue 85, was tested for the ready biological degradability in Closed Bottle Test.

Test performance

The test was performed according to: Method C.4E - Closed Bottle Test, Council Regulation (EC) No. 440/2008, published in O.J.L 142, 2008.

The results of biological degradation are related to experimentally determined COD values of the test and reference substance at the beginning of the test.

The test substance was sufficiently soluble in used mineral medium so the dosage from the stock solution was carried out.

Sodium benzoate was used as the reference substance. The dosage was carried out from the stock solution.

COD of the test substance in medium at the beginning of the main test:             0.761 mg·mg-1

COD of the reference substance in medium at the beginning of the main test:  1.643 mg·mg-1

In parallel to the main test the toxicity test was performed.

Based on the test substance contains nitrogen in the chemical composition, the oxidized nitrogen forms were determined and the correction for nitrification was carried out.

The test was performed at temperature of 20 ± 1 °C with the pH values of solutions 7 – 8 at the beginning of the test.

 

Validity of the test

The prescribed validity criteria in the test were fulfilled. The test substance was not inhibiting for the used inoculum.

Since all criteria of acceptability were met, this study is considered to be valid.

 

Test results

In this 28-day study of ready biological degradability the degradation of 22.8 % of the test substance, Direct Blue 85, was attained in the end of study.

Description of key information

In this 28-day study of ready biological degradability the degradation of 22.8 % of the test substance, Direct Blue 85, was attained in the end of study.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information