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Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
15/01/2010 - 12/02/2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted in accordance with an appropriate OECD test guideline and in compliance with GLP.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): Ethylthioethanol

- Physical state: Liquid

- Analytical purity: 99.29%

- Impurities (identity and concentrations): Ethylmercaptan <0.01%

- Composition of test material, percentage of components:

- Purity test date:

- Lot/batch No.: 2009-12-0530

- Expiration date of the lot/batch: Not given

- Storage condition of test material: Room temperature in the dark, under nitrogen

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Final effluent from Severn Trent Water Ltd sewage treatment plant, Lougborough, Leicestershire, UK

- Storage conditions: N/A

- Storage length: Effluent used immediately

- Preparation of inoculum for exposure: Filtration

- Water filtered:Yes

- Type and size of filter: Coarse filter paper
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
1.5 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS

- Composition of medium: See Table 1

- Test temperature: 20 °C

- Aeration of dilution water: Yes

- Continuous darkness: Yes


TEST SYSTEM

- Culturing apparatus: 250 - 300 ml BOD bottles (darkened glass) with ground glass stoppers

- Number of culture flasks/concentration: 2 per sampling date

- Measuring equipment: YSI 54A dissolved oxygen meter and BOD probe

- Test performed in closed vessels due to significant volatility of test substance: Yes


SAMPLING

- Sampling frequency: Days 0, 3, 5, 7, 11, 14, 18, 21, 24, 28

- Sample storage before analysis: No


CONTROL AND BLANK SYSTEM

- Inoculum blank: Inoculated culture medium

- Abiotic sterile control: None

- Toxicity control: Test item (1.5 mg/l) and reference substance (1.5 mg/l) in inoculated culture medium


STATISTICAL METHODS: Not required
Reference substance
Reference substance:
benzoic acid, sodium salt

Results and discussion

Preliminary study:
Not applicable
Test performance:
Not applicable
% Degradationopen allclose all
Parameter:
% degradation (O2 consumption)
Value:
10
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
15
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
7
Sampling time:
21 d
Parameter:
% degradation (O2 consumption)
Value:
8
Sampling time:
28 d
Details on results:
See Figure 1

BOD5 / COD results

Results with reference substance:
The reference substance attained 62% degradation by Day 14 and 69% by Day 28, thereby confirming the suitability of the test method and the culture medium.

Any other information on results incl. tables

The oxygen depletion of the inoculated control did not exceed 1.5 mg O2/l after 28 days, the residual oxygen concentration in the test bottles remained at 4.30 mg O2/l or greater in all test vessels, and the difference between the extremes of replicate oxygen depletion did not exceed 20% at the end of the test, thereby satisfying the validity criteria of the test.

The test item attained 8% degadation after 28 days and therefore cannot be considered readily biodegradable according to the criteria of the test guideline.

Variation in degradation rates on different sampling days was considered to be due to normal biological variation in respiration rates between control and test vessels.

The toxicity control attained 30% degradation after 14 days thereby confirming that the test item was not toxic to sewage microorganisms at the concentration used in the test.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
not inherently biodegradable
Conclusions:
In a GLP-compliant ready biodegradation test carried out in accordance with OECD Test Guideline 301D (closed bottle test), ethylthioethanol attained 8% degradation after 28 days. It therefore is not considered to be readily biodegradable. All relevant validity criteria were met.