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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:
From June 2017 to March 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
- Appearance: Pink liquid
- Test item storage: At room temperature protected from light
- Purity/Composition correction factor: No correction factor required
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on inoculum:
Chuan Yang River was used as source for the microbial inoculum
Duration of test (contact time):
28 d
Initial conc.:
5 mg/L
Based on:
test mat.
Initial conc.:
1.4 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST METHOD
Test solutions were prepared in glass bottles with volume of 10 liters. Each group of test solutions was immediately dispensed into 20 BOD bottles by hose from the lower quarter (not the bottom) of the glass bottle with a silicone tube. Air-bubble was avoided during the dispersion and all the BOD bottles were completely filled with test system solutions. After sealing with the stoppers (air-bubble free), the BOD bottles were incubated at 19.7-20.3°C in incubator. Dissolved oxygen, pH value and temperature of the test solutions were measured 0, 1, 4, 7, 11, 14, 18, 21, 25 and 28 day(s) after the test beginning by electrode method. Two bottles in each group at each time interval were removed from incubation for analysis. Oxygen consumption and biodegradation of each group were calculated.

INOCULUM
5 mL inoculum was introduced into 10 L test system, that is 0.5 mL/L (inoculum/mineral medium). The inoculated bacterial count in the test system was measured as 5.90 x 10000 cells/L.

MINERAL MEDIUM
- Stock solution A: 8.5 g/L KH2PO4, 21.75 g/L K2HPO4, 33.4 g/L Na2HPO4.2H2O, 0.5 g/L NH4Cl
- Stock solution B: 27.5 g/L CaCl2
- Stock solution C: 22.5 g/L MgSO4.7H2O
- Stock solution D: 0.25 g/L FeCl3.6H2O
- Mineral medium: 10 mL solution A + 1 mL solution B + 1 mL solution C + 1 mL solution D + ultrapure water up to 1L (pH adjusted to 7.4+/- 0.2 with a diluted hydrochloric acid solution)

TEST SYSTEM
- Inoculum blank: 20 replicates (mineral medium + inoculum)
- Test substance: 20 replicates (mineral medium + 5 mg/L test substance + inoculum)
- Procedure control (reference): 20 replicates (mineral medium + 2 mg/L reference substance + inoculum)
- Toxicity control: 20 replicates (mineral medium + 2 mg/L


Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
14 d

Test Substance Bottles

The average biodegradation percentage in the test substance bottles containing 5 mg/L of test substance was -1% on Day 14, -1% on Day 28.

Toxicity Control Bottles

The average biodegradation percentage in the toxicity control bottles containing 5 mg/L of test substance was 36% on Day 14. Therefore, the test item was not inhibitory to the activity of the microbial inoculum based on the test criteria (≥25% ThOD).

Method Validation

During the test, the temperature was maintained at 19.7-20.3°C. The mean oxygen depletion in inoculum blanks was 0.67 mg/L, less than 1.5 mg/L by the end of the test. Residual concentration of oxygen in BOD bottles did not fall below 0.5 mg/L during the test. The pH values were between 6.64 and 7.47. The difference between replicate values was within 20% during the test. The mean biodegradation of the reference substance was 85% by Day 14, which reached the pass level of ready biodegradation test (>60% within 14 days). The results of the inhibition control showed that the test substance met the criteria for not being inhibitory to the microbial inoculum. Thus, the test is considered valid.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
No biologically-relevant degradation of the test item was observed during the 28-day test period. Therefore, the test item should be considered not readily biodegradable under the conditions of the test
Executive summary:

The ultimate aerobic biodegradability of the test itemwas investigated in a GLP-compliant ready biodegradability screening study performed in accordance with OECD Guideline No. 301D. No biologically-relevant degradation of the test item was observed during the28-day test period. Therefore, the test item should be considered not readily biodegradable under theconditions of the test

Description of key information

The ultimate aerobic biodegradability of the test item was investigated in a GLP-compliant ready biodegradability screening study performed in accordance with OECD Guideline No. 301D. No biologically-relevant degradation of the test item was observed during the 28-day test period. Therefore, the test item should be considered not readily biodegradable under the conditions of the test.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

The ready biodegradability of the test item was investigated in a GLP-compliant study performed in accordance with OECD Guideline No. 301D, without deviations. The study is considered as reliable (Klimisch 1) and is selected as a key study for the endpoint.