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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:
March 25, 2019 to June 20, 2019
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)
Specific details on test material used for the study:
Test substance is a UVCB
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
Activated Sludge was obtained for Aeration tank of Da Tansha Sewage Treatment Plant of Guangzhou with batch no. IAs20190415-1. The activated sludge was treated as follows; Fresh sample of activated sludge was collected from the aeration tank of a sewage treatment plant. After removing any coarse particles and impurities on the surface, the sludge was washed with the test medium once (1100 g, 10 min), the supernatant liquid phase was decanted and the solids were re-suspended in the test medium. The suspended solids of the sludge concentration was determined and adjusted to 3.7 g/L. Thereafter, the sludge was kept in aeration until required. When testing, the inoculum was added to each test vessel to give a final concentration of 30 mg suspended solids per litre. The total number of bacteria in the test system was 1.1 x 10 7 CFU/L.
Duration of test (contact time):
28 d
Initial conc.:
23 mg/L
Based on:
test mat.
Initial conc.:
52 mg/L
Based on:
COD
Parameter followed for biodegradation estimation:
other: Oxygen uptake.
Details on study design:
There were 4 test groups in the study. They include;
Test suspension Bottles 1, 2, A containing test substance, inoculum and test medium
Inoculum blank bottles 3, 4,B Containing inoculum and test medium
Procedure Control, bottle 5, Containing reference substance, inoculum and test medium
Toxicity control bottle 6 Containing test substance, reference substance, inoculum and test medium

Test substance is liquid and insoluble in water, therefore it was weighed on a clean and dry cover glass and directly added into each test bottle for testing.
8.4 mg of the test substance was respectively weighed on a clean and dry cover glass, and added directly into the bottles 1, 2, A. Then 362 mL of test medium was respectively added into each bottle, and took them an ultrasound treatment for 10 min. 5.7 mg of the test substance was weighed on a clean and dry cover glass, and added directly into bottle 6. Then 241 mL of test medium was added into this bottle, and took it an ultrasound treatment for 10 min. The purity of the test substance is 100% (as UVCB).

The test substance concentration was 23 mg/L, giving 52 mg/L of COD. The reference substance concentration was 34 mg/L, giving 56 mg/L of ThOD. Total ThOD and COD of the toxicity control was 108 mg/L. The concentration of the inoculum was 30 mg/L in all vessels. All the test vessels were stained and incubated in the OxiTop® Control BOD Test System at 22°C± 1°C in the dark and closed condition over 28 days.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
77.8
Sampling time:
28 d
Details on results:
Under the conditions of the study, the percentage biodegradation of the test substance on 28 d were 84.3% and 71.2%, with a mean of 77.8%. At the start and end of the test, N02 --N and N03 --N concentrations of the test suspension and inoculum blank were determined. The results revealed that there were not nitrifications occurred, and the oxygen uptake from nitrification of the test suspension were -0.4 mg/L and -1.0 mg/L.

Percentage biodegradation (%)

 Time (d)   

 Test Suspension         

 Procedure control  Toxicity control
 bottle 1   bottle 2   Average  Difference  bottle 5  Bottle 6
 1  2.2  2.2  2.2  0  11.2  16.2
 2  3.8  5.0  4.4  1.2  54.8  29.7
 3  6.0  8.1  7.0  2.1  67.0  36.0
 4  8.1  11.4  9.7  3.3  73.4  40.6
 5  11.9  14.0  13.0  2.1  72.9  41.7
 6  14.6  14.6  14.6  0  76.4  43.5
 7  16.8  18.0  17.4  1.2  79.9  46.7
 8  19.0  20.2  19.6  1.2  79.5  46.5
 9  20.6  20.6  20.6  0  80.4  48.2
 10  23.5  23.5  23.5  0  84.1  50.1
 11  25.0  25.0  25.0  0  84.1  52.7
 12  27.8  27.8  27.8  0  84.6  52.9
 13  30.4  30.4  30.4  0  85.5  54.8
 14  35.8  35.8  35.8  0  87.0  58.2
 15  39.7  38.6  39.1  1.2  86.5  57..9
 16  45.2  42.9  44.0  2.3  88.0  60.0
17   50.5  47.2  48.8  33.3  86.5  61.8
 18  56.0  51.7  53.8  4.2  88.0  63.9
 19  60.4  53.8  57.1  6.5  89.5  64.6
 20  65.3  57.6  61.4  7.7  89.0  67.1
 21  68.5  60.8  64.6  7.7  89.5  68.6
 22  72.2  62.4  67.3  9.8  88.5  69.4
 23  74.9  65.1  70.0  9.8  85.4  70.4
 24  77.7  67.9  72.8  9.8  87.5  71.5
 25  79.4  69.6  74.5  9.8  91.4  74.8
26  81.4  70.7  76.1  10.8  89.9  74.0
 27  84.2  72.3  78.3  11.9  87.5

74.1 

 28  84.3  71.2  77.8  13.1  91.0  78.1
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Remarks:
REACH permits waiving the 10 window for multi constituent’s substances in cases where the components are defined as a homologous series of substances within a certain range of carbon chain length and/or degree of substitution. The test substance is considered to consist of components with different carbon chain lengths.
Conclusions:
The percentage biodegradation of the test substance on 28 d were 84.3% and 71.2%, with a mean of 77.8%. REACH permits waiving the 10 window for multi constituent’s substances in cases where the components are defined as a homologous series of substances within a certain range of carbon chain length and/or degree of substitution. The test substance is considered to consist of components with different carbon chain lengths.
Executive summary:

The biodegradation potential of the test substance was conducted in accordance with OECD 301F guidelines and in compliance with GLP principles. The study included 4 test groups; Test suspensions, inoculum blank, procedure and toxicity controls. Test substance concentration used was 23 mg/L (equivalent to 52 mg/L COD) and the concentration of the reference substance was 34 mg/L (equivalent to 56 mg/L of ThOD). Activated sludge was used as inoculum with a concentration of 30 mg/L suspended solids.  The total number of bacteria in the test system was 1.1x107CFU/L. The test was conducted for 28 days (in the dark and under sealed conditions) with a temperature of 22.0 °C - 22.9 °C (within 22 °C ± l 0 °C).  The pH values were 7.28 - 7.42 (at the start of the test), and 7.20 - 7.26 (at the end of the test).

 

The test satisfied all the validity criteria:

  1. The oxygen uptake of the inoculum blank was 16. 7 mg/L, which was less than 60 mg/L.
  2. At the end of the test, the pH values of each test bottle were 7.20 - 7.26 which were within the range of 6.0 - 8.5.
  3. The difference of extremes of replicate values of the removal of the test substance was less than 20% during the test.
  4. The percentage biodegradation of the procedure control and the toxicity control was 87.0% and 58.2% respectively, exceeding the pass levels of 60% and 25% within 14 days.

Under the conditions of the study, the percentage biodegradation of the test substance on Day 28 was determined to be 77.8 % (average of two replicates). Furthermore, since the test substance is a UVCB consisting of structurally similar chemicals, the 10-day window for ready biodegradability should not be applied to interpret the results of the test according to OECD guidance and the test substance could be considered to be readily biodegradable.”

Description of key information

The biodegradation potential of the test substance was conducted in accordance with OECD 301F guidelines and in compliance with GLP principles. The study included 4 test groups; Test suspensions, inoculum blank, procedure and toxicity controls. Test substance concentration used was 23 mg/L (equivalent to 52 mg/L COD) and the concentration of the reference substance was 34 mg/L (equivalent to 56 mg/L of ThOD). Activated sludge was used as inoculum with a concentration of 30 mg/L suspended solids.  The total number of bacteria in the test system was 1.1x107CFU/L. The test was conducted for 28 days (in the dark and under sealed conditions) with a temperature of 22.0 °C - 22.9 °C (within 22 °C ± l 0 °C).  The pH values were 7.28 - 7.42 (at the start of the test), and 7.20 - 7.26 (at the end of the test).

 

The test satisfied all the validity criteria:

  1. The oxygen uptake of the inoculum blank was 16. 7 mg/L, which was less than 60 mg/L.
  2. At the end of the test, the pH values of each test bottle were 7.20 - 7.26 which were within the range of 6.0 - 8.5.
  3. The difference of extremes of replicate values of the removal of the test substance was less than 20% during the test.
  4. The percentage biodegradation of the procedure control and the toxicity control was 87.0% and 58.2% respectively, exceeding the pass levels of 60% and 25% within 14 days.

Under the conditions of the study, the percentage biodegradation of the test substance on Day 28 was determined to be 77.8 % (average of two replicates). Furthermore, since the test substance is a UVCB consisting of structurally similar chemicals, the 10-day window for ready biodegradability should not be applied to interpret the results of the test according to OECD guidance and the test substance could be considered to be readily biodegradable.”

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

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